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Filipe Manana a045b6b197 btrfs: set last dir index to the current last index when opening dir 
commit 357950361c upstream.

When opening a directory for reading it, we set the last index where we
stop iteration to the value in struct btrfs_inode::index_cnt. That value
does not match the index of the most recently added directory entry but
it's instead the index number that will be assigned the next directory
entry.

This means that if after the call to opendir(3) new directory entries are
added, a readdir(3) call will return the first new directory entry. This
is fine because POSIX says the following [1]:

  "If a file is removed from or added to the directory after the most
   recent call to opendir() or rewinddir(), whether a subsequent call to
   readdir() returns an entry for that file is unspecified."

For example for the test script from commit 9b378f6ad4 ("btrfs: fix
infinite directory reads"), where we have 2000 files in a directory, ext4
doesn't return any new directory entry after opendir(3), while xfs returns
the first 13 new directory entries added after the opendir(3) call.

If we move to a shorter example with an empty directory when opendir(3) is
called, and 2 files added to the directory after the opendir(3) call, then
readdir(3) on btrfs will return the first file, ext4 and xfs return the 2
files (but in a different order). A test program for this, reported by
Ian Johnson, is the following:

   #include <dirent.h>
   #include <stdio.h>

   int main(void) {
     DIR *dir = opendir("test");

     FILE *file;
     file = fopen("test/1", "w");
     fwrite("1", 1, 1, file);
     fclose(file);

     file = fopen("test/2", "w");
     fwrite("2", 1, 1, file);
     fclose(file);

     struct dirent *entry;
     while ((entry = readdir(dir))) {
        printf("%s\n", entry->d_name);
     }
     closedir(dir);
     return 0;
   }

To make this less odd, change the behaviour to never return new entries
that were added after the opendir(3) call. This is done by setting the
last_index field of the struct btrfs_file_private attached to the
directory's file handle with a value matching btrfs_inode::index_cnt
minus 1, since that value always matches the index of the next new
directory entry and not the index of the most recently added entry.

[1] https://pubs.opengroup.org/onlinepubs/007904875/functions/readdir_r.html

Link: https://lore.kernel.org/linux-btrfs/YR1P0S.NGASEG570GJ8@ianjohnson.dev/
CC: stable@vger.kernel.org # 6.5+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2024-01-31 16:17:06 -08:00
arch LoongArch/smp: Call rcutree_report_cpu_starting() earlier 2024-01-31 16:17:03 -08:00
block block: Remove special-casing of compound pages 2024-01-25 15:27:52 -08:00
certs certs: Fix build error when PKCS#11 URI contains semicolon 2023-02-09 11:28:11 +01:00
crypto crypto: api - Disallow identical driver names 2024-01-31 16:16:58 -08:00
Documentation rename(): fix the locking of subdirectories 2024-01-31 16:17:02 -08:00
drivers net/mlx5e: fix a potential double-free in fs_any_create_groups 2024-01-31 16:17:05 -08:00
fs btrfs: set last dir index to the current last index when opening dir 2024-01-31 16:17:06 -08:00
include udp: fix busy polling 2024-01-31 16:17:04 -08:00
init rootfs: Fix support for rootfstype= when root= is given 2024-01-25 15:27:43 -08:00
io_uring io_uring/rw: ensure io->bytes_done is always initialized 2024-01-25 15:27:41 -08:00
ipc ipc: fix memory leak in init_mqueue_fs() 2022-12-31 13:32:01 +01:00
kernel rcu: Defer RCU kthreads wakeup when CPU is dying 2024-01-31 16:17:05 -08:00
lib kunit: debugfs: Fix unchecked dereference in debugfs_print_results() 2024-01-25 15:27:21 -08:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm: page_alloc: unreserve highatomic page blocks before oom 2024-01-31 16:17:03 -08:00
net netfilter: nft_limit: reject configurations that cause integer overflow 2024-01-31 16:17:05 -08:00
rust rust: allocator: Prevent mis-aligned allocation 2023-08-11 12:08:18 +02:00
samples fprobe: Pass entry_data to handlers 2023-10-25 12:03:12 +02:00
scripts scripts/get_abi: fix source path leak 2024-01-31 16:17:01 -08:00
security lsm: new security_file_ioctl_compat() hook 2024-01-31 16:17:00 -08:00
sound ASoC: mediatek: sof-common: Add NULL check for normal_link string 2024-01-25 15:27:48 -08:00
tools selftests: mlxsw: qos_pfc: Adjust the test to support 8 lanes 2024-01-25 15:27:51 -08:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt kvm/vfio: ensure kvg instance stays around in kvm_vfio_group_add() 2023-09-13 09:42:46 +02:00
.clang-format inet: ping: use hlist_nulls rcu iterator during lookup 2022-12-01 12:42:46 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Kbuild: add Rust support 2022-09-28 09:02:20 +02:00
.mailmap 9 hotfixes. 6 for MM, 3 for other areas. Four of these patches address 2022-12-10 17:10:52 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove Michal Marek from Kbuild maintainers 2022-11-16 14:53:00 +09:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS genirq/affinity: Move group_cpus_evenly() into lib/ 2024-01-10 17:10:33 +01:00
Makefile Linux 6.1.75 2024-01-25 15:27:52 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.