linux/fs/fat/dir.c

1467 lines
37 KiB

2005-09-06 15:17:12 -07:00
2005-09-06 15:17:12 -07:00
2005-09-06 15:17:12 -07:00
2005-09-06 15:17:12 -07:00
fat: use fat_msg_ratelimit() in fat__get_entry() If an application tries to lookup (opendir/readdir/stat) 5000 files on a fatfs USB device and the device is unplugged, many message occur, shown below. This makes the application slow. So use the new fat_msg_ratelimit() decrease the messaging rate. #> ./file_lookup_testcase ./files_directory/ usb 2-1.4: USB disconnect, device number 4 FAT-fs (sda1): FAT read failed (blocknr 2631) FAT-fs (sda1): Directory bread(block 396816) failed FAT-fs (sda1): Directory bread(block 396817) failed FAT-fs (sda1): Directory bread(block 396818) failed FAT-fs (sda1): Directory bread(block 396819) failed FAT-fs (sda1): Directory bread(block 396820) failed FAT-fs (sda1): Directory bread(block 396821) failed FAT-fs (sda1): Directory bread(block 396822) failed FAT-fs (sda1): Directory bread(block 396823) failed FAT-fs (sda1): Directory bread(block 406824) failed FAT-fs (sda1): Directory bread(block 406825) failed FAT-fs (sda1): Directory bread(block 406826) failed FAT-fs (sda1): Directory bread(block 406827) failed FAT-fs (sda1): Directory bread(block 406828) failed FAT-fs (sda1): Directory bread(block 406829) failed FAT-fs (sda1): Directory bread(block 406830) failed FAT-fs (sda1): Directory bread(block 406831) failed FAT-fs (sda1): Directory bread(block 417696) failed FAT-fs (sda1): Directory bread(block 417697) failed FAT-fs (sda1): Directory bread(block 417698) failed FAT-fs (sda1): Directory bread(block 417699) failed FAT-fs (sda1): Directory bread(block 417700) failed FAT-fs (sda1): Directory bread(block 417701) failed FAT-fs (sda1): Directory bread(block 417702) failed FAT-fs (sda1): Directory bread(block 417703) failed FAT-fs (sda1): FAT read failed (blocknr 2631) FAT-fs (sda1): Directory bread(block 396816) failed FAT-fs (sda1): Directory bread(block 396817) failed FAT-fs (sda1): Directory bread(block 396818) failed FAT-fs (sda1): Directory bread(block 396819) failed FAT-fs (sda1): Directory bread(block 396820) failed FAT-fs (sda1): Directory bread(block 396821) failed Signed-off-by: Namjae Jeon <linkinjeon@gmail.com> Signed-off-by: Amit Sahrawat <amit.sahrawat83@gmail.com> Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-05-31 16:26:14 -07:00
fat: stop reading directory entries past the end-of-directory marker The FAT specification[1] (FAT Directory Structure -> "DIR_Name[0]") states: If DIR_Name[0] == 0x00, then the directory entry is free (same as for 0xE5), and there are no allocated directory entries after this one (all of the DIR_Name[0] bytes in all of the entries after this one are also set to 0). The special 0 value, rather than the 0xE5 value, indicates to FAT file system driver code that the rest of the entries in this directory do not need to be examined because they are all free. Linux did not honour this. fat_get_entry() kept advancing past the 0x00 terminator; if the trailing on-disk slots were not zero-filled (buggy formatters, read-only media written by other operating systems, on-disk corruption) the driver surfaced arbitrary bytes as real directory entries. On a typical affected image, `ls /mnt` returns ~150 bogus entries with random binary names, multi-gigabyte sizes, dates ranging from 1980 to 2106, and a flood of -EIO from stat(). Earlier attempts (v1..v3, see [2][3][4]) added `de->name[0] == 0` guards at each call site. As Hirofumi pointed out on v3, those guards reject the entry but fat_get_entry() has already advanced *pos past it; the next readdir() resumes after the marker and walks straight back into the garbage. His suggestion was to centralise the check. This patch: * Adds fat_get_entry_eod(), a small wrapper around fat_get_entry() that returns -1 when name[0] == 0 and seeks *pos to dir->i_size. Per spec every slot after the 0x00 marker is also zero, so jumping to the end of the directory is correct: subsequent reads return -1 from fat_bmap() without re-fetching trailing zero slots, and callers persisting *pos across invocations (notably readdir's ctx->pos) keep reporting end-of-directory on re-entry. * Converts the read/search paths to use the new wrapper: fat_parse_long(), fat_search_long(), __fat_readdir(), and fat_get_short_entry() -- the last covers fat_get_dotdot_entry(), fat_dir_empty(), fat_subdirs(), fat_scan(), and fat_scan_logstart() transitively. * Leaves fat_add_entries() and __fat_remove_entries() on raw fat_get_entry(): the write paths legitimately need to operate on free/zero slots. fat_add_entries() additionally detects an allocated entry past a 0x00 marker (the spec violation that produces the garbage) and treats it as filesystem corruption: fat_fs_error_ratelimit() is called -- which honours the configured errors= mount option (panic / remount-ro / continue) -- and the operation returns -EIO so we don't write fresh entries into an already-corrupt directory. [1] https://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/fatgen103.doc [2] https://lore.kernel.org/lkml/20181207013410.7050-1-mcroce@redhat.com/ [3] https://lore.kernel.org/lkml/20181216231510.26854-1-mcroce@redhat.com/ [4] https://lore.kernel.org/lkml/20190201001408.7453-1-mcroce@redhat.com/ Reported-by: Timothy Redaelli <tredaelli@redhat.com> Suggested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Matteo Croce <teknoraver@meta.com> Link: https://patch.msgid.link/20260616163346.32603-1-technoboy85@gmail.com Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
2026-06-16 18:33:46 +02:00
fat: stop reading directory entries past the end-of-directory marker The FAT specification[1] (FAT Directory Structure -> "DIR_Name[0]") states: If DIR_Name[0] == 0x00, then the directory entry is free (same as for 0xE5), and there are no allocated directory entries after this one (all of the DIR_Name[0] bytes in all of the entries after this one are also set to 0). The special 0 value, rather than the 0xE5 value, indicates to FAT file system driver code that the rest of the entries in this directory do not need to be examined because they are all free. Linux did not honour this. fat_get_entry() kept advancing past the 0x00 terminator; if the trailing on-disk slots were not zero-filled (buggy formatters, read-only media written by other operating systems, on-disk corruption) the driver surfaced arbitrary bytes as real directory entries. On a typical affected image, `ls /mnt` returns ~150 bogus entries with random binary names, multi-gigabyte sizes, dates ranging from 1980 to 2106, and a flood of -EIO from stat(). Earlier attempts (v1..v3, see [2][3][4]) added `de->name[0] == 0` guards at each call site. As Hirofumi pointed out on v3, those guards reject the entry but fat_get_entry() has already advanced *pos past it; the next readdir() resumes after the marker and walks straight back into the garbage. His suggestion was to centralise the check. This patch: * Adds fat_get_entry_eod(), a small wrapper around fat_get_entry() that returns -1 when name[0] == 0 and seeks *pos to dir->i_size. Per spec every slot after the 0x00 marker is also zero, so jumping to the end of the directory is correct: subsequent reads return -1 from fat_bmap() without re-fetching trailing zero slots, and callers persisting *pos across invocations (notably readdir's ctx->pos) keep reporting end-of-directory on re-entry. * Converts the read/search paths to use the new wrapper: fat_parse_long(), fat_search_long(), __fat_readdir(), and fat_get_short_entry() -- the last covers fat_get_dotdot_entry(), fat_dir_empty(), fat_subdirs(), fat_scan(), and fat_scan_logstart() transitively. * Leaves fat_add_entries() and __fat_remove_entries() on raw fat_get_entry(): the write paths legitimately need to operate on free/zero slots. fat_add_entries() additionally detects an allocated entry past a 0x00 marker (the spec violation that produces the garbage) and treats it as filesystem corruption: fat_fs_error_ratelimit() is called -- which honours the configured errors= mount option (panic / remount-ro / continue) -- and the operation returns -EIO so we don't write fresh entries into an already-corrupt directory. [1] https://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/fatgen103.doc [2] https://lore.kernel.org/lkml/20181207013410.7050-1-mcroce@redhat.com/ [3] https://lore.kernel.org/lkml/20181216231510.26854-1-mcroce@redhat.com/ [4] https://lore.kernel.org/lkml/20190201001408.7453-1-mcroce@redhat.com/ Reported-by: Timothy Redaelli <tredaelli@redhat.com> Suggested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Matteo Croce <teknoraver@meta.com> Link: https://patch.msgid.link/20260616163346.32603-1-technoboy85@gmail.com Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
2026-06-16 18:33:46 +02:00
fat: stop reading directory entries past the end-of-directory marker The FAT specification[1] (FAT Directory Structure -> "DIR_Name[0]") states: If DIR_Name[0] == 0x00, then the directory entry is free (same as for 0xE5), and there are no allocated directory entries after this one (all of the DIR_Name[0] bytes in all of the entries after this one are also set to 0). The special 0 value, rather than the 0xE5 value, indicates to FAT file system driver code that the rest of the entries in this directory do not need to be examined because they are all free. Linux did not honour this. fat_get_entry() kept advancing past the 0x00 terminator; if the trailing on-disk slots were not zero-filled (buggy formatters, read-only media written by other operating systems, on-disk corruption) the driver surfaced arbitrary bytes as real directory entries. On a typical affected image, `ls /mnt` returns ~150 bogus entries with random binary names, multi-gigabyte sizes, dates ranging from 1980 to 2106, and a flood of -EIO from stat(). Earlier attempts (v1..v3, see [2][3][4]) added `de->name[0] == 0` guards at each call site. As Hirofumi pointed out on v3, those guards reject the entry but fat_get_entry() has already advanced *pos past it; the next readdir() resumes after the marker and walks straight back into the garbage. His suggestion was to centralise the check. This patch: * Adds fat_get_entry_eod(), a small wrapper around fat_get_entry() that returns -1 when name[0] == 0 and seeks *pos to dir->i_size. Per spec every slot after the 0x00 marker is also zero, so jumping to the end of the directory is correct: subsequent reads return -1 from fat_bmap() without re-fetching trailing zero slots, and callers persisting *pos across invocations (notably readdir's ctx->pos) keep reporting end-of-directory on re-entry. * Converts the read/search paths to use the new wrapper: fat_parse_long(), fat_search_long(), __fat_readdir(), and fat_get_short_entry() -- the last covers fat_get_dotdot_entry(), fat_dir_empty(), fat_subdirs(), fat_scan(), and fat_scan_logstart() transitively. * Leaves fat_add_entries() and __fat_remove_entries() on raw fat_get_entry(): the write paths legitimately need to operate on free/zero slots. fat_add_entries() additionally detects an allocated entry past a 0x00 marker (the spec violation that produces the garbage) and treats it as filesystem corruption: fat_fs_error_ratelimit() is called -- which honours the configured errors= mount option (panic / remount-ro / continue) -- and the operation returns -EIO so we don't write fresh entries into an already-corrupt directory. [1] https://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/fatgen103.doc [2] https://lore.kernel.org/lkml/20181207013410.7050-1-mcroce@redhat.com/ [3] https://lore.kernel.org/lkml/20181216231510.26854-1-mcroce@redhat.com/ [4] https://lore.kernel.org/lkml/20190201001408.7453-1-mcroce@redhat.com/ Reported-by: Timothy Redaelli <tredaelli@redhat.com> Suggested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Matteo Croce <teknoraver@meta.com> Link: https://patch.msgid.link/20260616163346.32603-1-technoboy85@gmail.com Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
2026-06-16 18:33:46 +02:00
fat: stop reading directory entries past the end-of-directory marker The FAT specification[1] (FAT Directory Structure -> "DIR_Name[0]") states: If DIR_Name[0] == 0x00, then the directory entry is free (same as for 0xE5), and there are no allocated directory entries after this one (all of the DIR_Name[0] bytes in all of the entries after this one are also set to 0). The special 0 value, rather than the 0xE5 value, indicates to FAT file system driver code that the rest of the entries in this directory do not need to be examined because they are all free. Linux did not honour this. fat_get_entry() kept advancing past the 0x00 terminator; if the trailing on-disk slots were not zero-filled (buggy formatters, read-only media written by other operating systems, on-disk corruption) the driver surfaced arbitrary bytes as real directory entries. On a typical affected image, `ls /mnt` returns ~150 bogus entries with random binary names, multi-gigabyte sizes, dates ranging from 1980 to 2106, and a flood of -EIO from stat(). Earlier attempts (v1..v3, see [2][3][4]) added `de->name[0] == 0` guards at each call site. As Hirofumi pointed out on v3, those guards reject the entry but fat_get_entry() has already advanced *pos past it; the next readdir() resumes after the marker and walks straight back into the garbage. His suggestion was to centralise the check. This patch: * Adds fat_get_entry_eod(), a small wrapper around fat_get_entry() that returns -1 when name[0] == 0 and seeks *pos to dir->i_size. Per spec every slot after the 0x00 marker is also zero, so jumping to the end of the directory is correct: subsequent reads return -1 from fat_bmap() without re-fetching trailing zero slots, and callers persisting *pos across invocations (notably readdir's ctx->pos) keep reporting end-of-directory on re-entry. * Converts the read/search paths to use the new wrapper: fat_parse_long(), fat_search_long(), __fat_readdir(), and fat_get_short_entry() -- the last covers fat_get_dotdot_entry(), fat_dir_empty(), fat_subdirs(), fat_scan(), and fat_scan_logstart() transitively. * Leaves fat_add_entries() and __fat_remove_entries() on raw fat_get_entry(): the write paths legitimately need to operate on free/zero slots. fat_add_entries() additionally detects an allocated entry past a 0x00 marker (the spec violation that produces the garbage) and treats it as filesystem corruption: fat_fs_error_ratelimit() is called -- which honours the configured errors= mount option (panic / remount-ro / continue) -- and the operation returns -EIO so we don't write fresh entries into an already-corrupt directory. [1] https://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/fatgen103.doc [2] https://lore.kernel.org/lkml/20181207013410.7050-1-mcroce@redhat.com/ [3] https://lore.kernel.org/lkml/20181216231510.26854-1-mcroce@redhat.com/ [4] https://lore.kernel.org/lkml/20190201001408.7453-1-mcroce@redhat.com/ Reported-by: Timothy Redaelli <tredaelli@redhat.com> Suggested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Matteo Croce <teknoraver@meta.com> Link: https://patch.msgid.link/20260616163346.32603-1-technoboy85@gmail.com Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
2026-06-16 18:33:46 +02:00
2005-09-06 15:17:12 -07:00
2022-03-23 16:06:26 -07:00
fat: stop reading directory entries past the end-of-directory marker The FAT specification[1] (FAT Directory Structure -> "DIR_Name[0]") states: If DIR_Name[0] == 0x00, then the directory entry is free (same as for 0xE5), and there are no allocated directory entries after this one (all of the DIR_Name[0] bytes in all of the entries after this one are also set to 0). The special 0 value, rather than the 0xE5 value, indicates to FAT file system driver code that the rest of the entries in this directory do not need to be examined because they are all free. Linux did not honour this. fat_get_entry() kept advancing past the 0x00 terminator; if the trailing on-disk slots were not zero-filled (buggy formatters, read-only media written by other operating systems, on-disk corruption) the driver surfaced arbitrary bytes as real directory entries. On a typical affected image, `ls /mnt` returns ~150 bogus entries with random binary names, multi-gigabyte sizes, dates ranging from 1980 to 2106, and a flood of -EIO from stat(). Earlier attempts (v1..v3, see [2][3][4]) added `de->name[0] == 0` guards at each call site. As Hirofumi pointed out on v3, those guards reject the entry but fat_get_entry() has already advanced *pos past it; the next readdir() resumes after the marker and walks straight back into the garbage. His suggestion was to centralise the check. This patch: * Adds fat_get_entry_eod(), a small wrapper around fat_get_entry() that returns -1 when name[0] == 0 and seeks *pos to dir->i_size. Per spec every slot after the 0x00 marker is also zero, so jumping to the end of the directory is correct: subsequent reads return -1 from fat_bmap() without re-fetching trailing zero slots, and callers persisting *pos across invocations (notably readdir's ctx->pos) keep reporting end-of-directory on re-entry. * Converts the read/search paths to use the new wrapper: fat_parse_long(), fat_search_long(), __fat_readdir(), and fat_get_short_entry() -- the last covers fat_get_dotdot_entry(), fat_dir_empty(), fat_subdirs(), fat_scan(), and fat_scan_logstart() transitively. * Leaves fat_add_entries() and __fat_remove_entries() on raw fat_get_entry(): the write paths legitimately need to operate on free/zero slots. fat_add_entries() additionally detects an allocated entry past a 0x00 marker (the spec violation that produces the garbage) and treats it as filesystem corruption: fat_fs_error_ratelimit() is called -- which honours the configured errors= mount option (panic / remount-ro / continue) -- and the operation returns -EIO so we don't write fresh entries into an already-corrupt directory. [1] https://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/fatgen103.doc [2] https://lore.kernel.org/lkml/20181207013410.7050-1-mcroce@redhat.com/ [3] https://lore.kernel.org/lkml/20181216231510.26854-1-mcroce@redhat.com/ [4] https://lore.kernel.org/lkml/20190201001408.7453-1-mcroce@redhat.com/ Reported-by: Timothy Redaelli <tredaelli@redhat.com> Suggested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Matteo Croce <teknoraver@meta.com> Link: https://patch.msgid.link/20260616163346.32603-1-technoboy85@gmail.com Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
2026-06-16 18:33:46 +02:00
treewide: Remove uninitialized_var() usage Using uninitialized_var() is dangerous as it papers over real bugs[1] (or can in the future), and suppresses unrelated compiler warnings (e.g. "unused variable"). If the compiler thinks it is uninitialized, either simply initialize the variable or make compiler changes. In preparation for removing[2] the[3] macro[4], remove all remaining needless uses with the following script: git grep '\buninitialized_var\b' | cut -d: -f1 | sort -u | \ xargs perl -pi -e \ 's/\buninitialized_var\(([^\)]+)\)/\1/g; s:\s*/\* (GCC be quiet|to make compiler happy) \*/$::g;' drivers/video/fbdev/riva/riva_hw.c was manually tweaked to avoid pathological white-space. No outstanding warnings were found building allmodconfig with GCC 9.3.0 for x86_64, i386, arm64, arm, powerpc, powerpc64le, s390x, mips, sparc64, alpha, and m68k. [1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/ [2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/ [3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/ [4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/ Reviewed-by: Leon Romanovsky <leonro@mellanox.com> # drivers/infiniband and mlx4/mlx5 Acked-by: Jason Gunthorpe <jgg@mellanox.com> # IB Acked-by: Kalle Valo <kvalo@codeaurora.org> # wireless drivers Reviewed-by: Chao Yu <yuchao0@huawei.com> # erofs Signed-off-by: Kees Cook <keescook@chromium.org>
2020-06-03 13:09:38 -07:00
fat: stop reading directory entries past the end-of-directory marker The FAT specification[1] (FAT Directory Structure -> "DIR_Name[0]") states: If DIR_Name[0] == 0x00, then the directory entry is free (same as for 0xE5), and there are no allocated directory entries after this one (all of the DIR_Name[0] bytes in all of the entries after this one are also set to 0). The special 0 value, rather than the 0xE5 value, indicates to FAT file system driver code that the rest of the entries in this directory do not need to be examined because they are all free. Linux did not honour this. fat_get_entry() kept advancing past the 0x00 terminator; if the trailing on-disk slots were not zero-filled (buggy formatters, read-only media written by other operating systems, on-disk corruption) the driver surfaced arbitrary bytes as real directory entries. On a typical affected image, `ls /mnt` returns ~150 bogus entries with random binary names, multi-gigabyte sizes, dates ranging from 1980 to 2106, and a flood of -EIO from stat(). Earlier attempts (v1..v3, see [2][3][4]) added `de->name[0] == 0` guards at each call site. As Hirofumi pointed out on v3, those guards reject the entry but fat_get_entry() has already advanced *pos past it; the next readdir() resumes after the marker and walks straight back into the garbage. His suggestion was to centralise the check. This patch: * Adds fat_get_entry_eod(), a small wrapper around fat_get_entry() that returns -1 when name[0] == 0 and seeks *pos to dir->i_size. Per spec every slot after the 0x00 marker is also zero, so jumping to the end of the directory is correct: subsequent reads return -1 from fat_bmap() without re-fetching trailing zero slots, and callers persisting *pos across invocations (notably readdir's ctx->pos) keep reporting end-of-directory on re-entry. * Converts the read/search paths to use the new wrapper: fat_parse_long(), fat_search_long(), __fat_readdir(), and fat_get_short_entry() -- the last covers fat_get_dotdot_entry(), fat_dir_empty(), fat_subdirs(), fat_scan(), and fat_scan_logstart() transitively. * Leaves fat_add_entries() and __fat_remove_entries() on raw fat_get_entry(): the write paths legitimately need to operate on free/zero slots. fat_add_entries() additionally detects an allocated entry past a 0x00 marker (the spec violation that produces the garbage) and treats it as filesystem corruption: fat_fs_error_ratelimit() is called -- which honours the configured errors= mount option (panic / remount-ro / continue) -- and the operation returns -EIO so we don't write fresh entries into an already-corrupt directory. [1] https://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/fatgen103.doc [2] https://lore.kernel.org/lkml/20181207013410.7050-1-mcroce@redhat.com/ [3] https://lore.kernel.org/lkml/20181216231510.26854-1-mcroce@redhat.com/ [4] https://lore.kernel.org/lkml/20190201001408.7453-1-mcroce@redhat.com/ Reported-by: Timothy Redaelli <tredaelli@redhat.com> Suggested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Matteo Croce <teknoraver@meta.com> Link: https://patch.msgid.link/20260616163346.32603-1-technoboy85@gmail.com Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
2026-06-16 18:33:46 +02:00
fat: stop reading directory entries past the end-of-directory marker The FAT specification[1] (FAT Directory Structure -> "DIR_Name[0]") states: If DIR_Name[0] == 0x00, then the directory entry is free (same as for 0xE5), and there are no allocated directory entries after this one (all of the DIR_Name[0] bytes in all of the entries after this one are also set to 0). The special 0 value, rather than the 0xE5 value, indicates to FAT file system driver code that the rest of the entries in this directory do not need to be examined because they are all free. Linux did not honour this. fat_get_entry() kept advancing past the 0x00 terminator; if the trailing on-disk slots were not zero-filled (buggy formatters, read-only media written by other operating systems, on-disk corruption) the driver surfaced arbitrary bytes as real directory entries. On a typical affected image, `ls /mnt` returns ~150 bogus entries with random binary names, multi-gigabyte sizes, dates ranging from 1980 to 2106, and a flood of -EIO from stat(). Earlier attempts (v1..v3, see [2][3][4]) added `de->name[0] == 0` guards at each call site. As Hirofumi pointed out on v3, those guards reject the entry but fat_get_entry() has already advanced *pos past it; the next readdir() resumes after the marker and walks straight back into the garbage. His suggestion was to centralise the check. This patch: * Adds fat_get_entry_eod(), a small wrapper around fat_get_entry() that returns -1 when name[0] == 0 and seeks *pos to dir->i_size. Per spec every slot after the 0x00 marker is also zero, so jumping to the end of the directory is correct: subsequent reads return -1 from fat_bmap() without re-fetching trailing zero slots, and callers persisting *pos across invocations (notably readdir's ctx->pos) keep reporting end-of-directory on re-entry. * Converts the read/search paths to use the new wrapper: fat_parse_long(), fat_search_long(), __fat_readdir(), and fat_get_short_entry() -- the last covers fat_get_dotdot_entry(), fat_dir_empty(), fat_subdirs(), fat_scan(), and fat_scan_logstart() transitively. * Leaves fat_add_entries() and __fat_remove_entries() on raw fat_get_entry(): the write paths legitimately need to operate on free/zero slots. fat_add_entries() additionally detects an allocated entry past a 0x00 marker (the spec violation that produces the garbage) and treats it as filesystem corruption: fat_fs_error_ratelimit() is called -- which honours the configured errors= mount option (panic / remount-ro / continue) -- and the operation returns -EIO so we don't write fresh entries into an already-corrupt directory. [1] https://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/fatgen103.doc [2] https://lore.kernel.org/lkml/20181207013410.7050-1-mcroce@redhat.com/ [3] https://lore.kernel.org/lkml/20181216231510.26854-1-mcroce@redhat.com/ [4] https://lore.kernel.org/lkml/20190201001408.7453-1-mcroce@redhat.com/ Reported-by: Timothy Redaelli <tredaelli@redhat.com> Suggested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Matteo Croce <teknoraver@meta.com> Link: https://patch.msgid.link/20260616163346.32603-1-technoboy85@gmail.com Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
2026-06-16 18:33:46 +02:00
fat: stop reading directory entries past the end-of-directory marker The FAT specification[1] (FAT Directory Structure -> "DIR_Name[0]") states: If DIR_Name[0] == 0x00, then the directory entry is free (same as for 0xE5), and there are no allocated directory entries after this one (all of the DIR_Name[0] bytes in all of the entries after this one are also set to 0). The special 0 value, rather than the 0xE5 value, indicates to FAT file system driver code that the rest of the entries in this directory do not need to be examined because they are all free. Linux did not honour this. fat_get_entry() kept advancing past the 0x00 terminator; if the trailing on-disk slots were not zero-filled (buggy formatters, read-only media written by other operating systems, on-disk corruption) the driver surfaced arbitrary bytes as real directory entries. On a typical affected image, `ls /mnt` returns ~150 bogus entries with random binary names, multi-gigabyte sizes, dates ranging from 1980 to 2106, and a flood of -EIO from stat(). Earlier attempts (v1..v3, see [2][3][4]) added `de->name[0] == 0` guards at each call site. As Hirofumi pointed out on v3, those guards reject the entry but fat_get_entry() has already advanced *pos past it; the next readdir() resumes after the marker and walks straight back into the garbage. His suggestion was to centralise the check. This patch: * Adds fat_get_entry_eod(), a small wrapper around fat_get_entry() that returns -1 when name[0] == 0 and seeks *pos to dir->i_size. Per spec every slot after the 0x00 marker is also zero, so jumping to the end of the directory is correct: subsequent reads return -1 from fat_bmap() without re-fetching trailing zero slots, and callers persisting *pos across invocations (notably readdir's ctx->pos) keep reporting end-of-directory on re-entry. * Converts the read/search paths to use the new wrapper: fat_parse_long(), fat_search_long(), __fat_readdir(), and fat_get_short_entry() -- the last covers fat_get_dotdot_entry(), fat_dir_empty(), fat_subdirs(), fat_scan(), and fat_scan_logstart() transitively. * Leaves fat_add_entries() and __fat_remove_entries() on raw fat_get_entry(): the write paths legitimately need to operate on free/zero slots. fat_add_entries() additionally detects an allocated entry past a 0x00 marker (the spec violation that produces the garbage) and treats it as filesystem corruption: fat_fs_error_ratelimit() is called -- which honours the configured errors= mount option (panic / remount-ro / continue) -- and the operation returns -EIO so we don't write fresh entries into an already-corrupt directory. [1] https://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/fatgen103.doc [2] https://lore.kernel.org/lkml/20181207013410.7050-1-mcroce@redhat.com/ [3] https://lore.kernel.org/lkml/20181216231510.26854-1-mcroce@redhat.com/ [4] https://lore.kernel.org/lkml/20190201001408.7453-1-mcroce@redhat.com/ Reported-by: Timothy Redaelli <tredaelli@redhat.com> Suggested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Matteo Croce <teknoraver@meta.com> Link: https://patch.msgid.link/20260616163346.32603-1-technoboy85@gmail.com Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
2026-06-16 18:33:46 +02:00
fat: stop reading directory entries past the end-of-directory marker The FAT specification[1] (FAT Directory Structure -> "DIR_Name[0]") states: If DIR_Name[0] == 0x00, then the directory entry is free (same as for 0xE5), and there are no allocated directory entries after this one (all of the DIR_Name[0] bytes in all of the entries after this one are also set to 0). The special 0 value, rather than the 0xE5 value, indicates to FAT file system driver code that the rest of the entries in this directory do not need to be examined because they are all free. Linux did not honour this. fat_get_entry() kept advancing past the 0x00 terminator; if the trailing on-disk slots were not zero-filled (buggy formatters, read-only media written by other operating systems, on-disk corruption) the driver surfaced arbitrary bytes as real directory entries. On a typical affected image, `ls /mnt` returns ~150 bogus entries with random binary names, multi-gigabyte sizes, dates ranging from 1980 to 2106, and a flood of -EIO from stat(). Earlier attempts (v1..v3, see [2][3][4]) added `de->name[0] == 0` guards at each call site. As Hirofumi pointed out on v3, those guards reject the entry but fat_get_entry() has already advanced *pos past it; the next readdir() resumes after the marker and walks straight back into the garbage. His suggestion was to centralise the check. This patch: * Adds fat_get_entry_eod(), a small wrapper around fat_get_entry() that returns -1 when name[0] == 0 and seeks *pos to dir->i_size. Per spec every slot after the 0x00 marker is also zero, so jumping to the end of the directory is correct: subsequent reads return -1 from fat_bmap() without re-fetching trailing zero slots, and callers persisting *pos across invocations (notably readdir's ctx->pos) keep reporting end-of-directory on re-entry. * Converts the read/search paths to use the new wrapper: fat_parse_long(), fat_search_long(), __fat_readdir(), and fat_get_short_entry() -- the last covers fat_get_dotdot_entry(), fat_dir_empty(), fat_subdirs(), fat_scan(), and fat_scan_logstart() transitively. * Leaves fat_add_entries() and __fat_remove_entries() on raw fat_get_entry(): the write paths legitimately need to operate on free/zero slots. fat_add_entries() additionally detects an allocated entry past a 0x00 marker (the spec violation that produces the garbage) and treats it as filesystem corruption: fat_fs_error_ratelimit() is called -- which honours the configured errors= mount option (panic / remount-ro / continue) -- and the operation returns -EIO so we don't write fresh entries into an already-corrupt directory. [1] https://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/fatgen103.doc [2] https://lore.kernel.org/lkml/20181207013410.7050-1-mcroce@redhat.com/ [3] https://lore.kernel.org/lkml/20181216231510.26854-1-mcroce@redhat.com/ [4] https://lore.kernel.org/lkml/20190201001408.7453-1-mcroce@redhat.com/ Reported-by: Timothy Redaelli <tredaelli@redhat.com> Suggested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Matteo Croce <teknoraver@meta.com> Link: https://patch.msgid.link/20260616163346.32603-1-technoboy85@gmail.com Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
2026-06-16 18:33:46 +02:00