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Artem Sadovnikov 16d9067f00 ext4: fix off-by-one error in do_split 
commit 94824ac9a8 upstream.

Syzkaller detected a use-after-free issue in ext4_insert_dentry that was
caused by out-of-bounds access due to incorrect splitting in do_split.

BUG: KASAN: use-after-free in ext4_insert_dentry+0x36a/0x6d0 fs/ext4/namei.c:2109
Write of size 251 at addr ffff888074572f14 by task syz-executor335/5847

CPU: 0 UID: 0 PID: 5847 Comm: syz-executor335 Not tainted 6.12.0-rc6-syzkaller-00318-ga9cda7c0ffed #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:377 [inline]
 print_report+0x169/0x550 mm/kasan/report.c:488
 kasan_report+0x143/0x180 mm/kasan/report.c:601
 kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
 __asan_memcpy+0x40/0x70 mm/kasan/shadow.c:106
 ext4_insert_dentry+0x36a/0x6d0 fs/ext4/namei.c:2109
 add_dirent_to_buf+0x3d9/0x750 fs/ext4/namei.c:2154
 make_indexed_dir+0xf98/0x1600 fs/ext4/namei.c:2351
 ext4_add_entry+0x222a/0x25d0 fs/ext4/namei.c:2455
 ext4_add_nondir+0x8d/0x290 fs/ext4/namei.c:2796
 ext4_symlink+0x920/0xb50 fs/ext4/namei.c:3431
 vfs_symlink+0x137/0x2e0 fs/namei.c:4615
 do_symlinkat+0x222/0x3a0 fs/namei.c:4641
 __do_sys_symlink fs/namei.c:4662 [inline]
 __se_sys_symlink fs/namei.c:4660 [inline]
 __x64_sys_symlink+0x7a/0x90 fs/namei.c:4660
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
 </TASK>

The following loop is located right above 'if' statement.

for (i = count-1; i >= 0; i--) {
	/* is more than half of this entry in 2nd half of the block? */
	if (size + map[i].size/2 > blocksize/2)
		break;
	size += map[i].size;
	move++;
}

'i' in this case could go down to -1, in which case sum of active entries
wouldn't exceed half the block size, but previous behaviour would also do
split in half if sum would exceed at the very last block, which in case of
having too many long name files in a single block could lead to
out-of-bounds access and following use-after-free.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Cc: stable@vger.kernel.org
Fixes: 5872331b3d ("ext4: fix potential negative array index in do_split()")
Signed-off-by: Artem Sadovnikov <a.sadovnikov@ispras.ru>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20250404082804.2567-3-a.sadovnikov@ispras.ru
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-04-20 10:15:42 +02:00
arch KVM: arm64: Tear down vGIC on failed vCPU creation 2025-04-20 10:15:34 +02:00
block block: fix 'kmem_cache of name 'bio-108' already exists' 2025-03-22 12:54:21 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: api - Fix larval relookup type and mask 2025-04-10 14:39:20 +02:00
Documentation dt-bindings: media: st,stmipid02: correct lane-polarities maxItems 2025-04-20 10:15:32 +02:00
drivers bus: mhi: host: Fix race between unprepare and queue_buf 2025-04-20 10:15:42 +02:00
fs ext4: fix off-by-one error in do_split 2025-04-20 10:15:42 +02:00
include io_uring/net: fix io_req_post_cqe abuse by send bundle 2025-04-20 10:15:40 +02:00
init ARM: 9443/1: Require linker to support KEEP within OVERLAY for DCE 2025-04-10 14:39:40 +02:00
io_uring io_uring/kbuf: reject zero sized provided buffers 2025-04-20 10:15:40 +02:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-05 14:03:02 +01:00
kernel tracing: probe-events: Add comments about entry data storing code 2025-04-20 10:15:27 +02:00
lib zstd: Increase DYNAMIC_BMI2 GCC version cutoff from 4.8 to 11.0 to work around compiler segfault 2025-04-20 10:15:12 +02:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm: zswap: fix crypto_free_acomp() deadlock in zswap_cpu_comp_dead() 2025-04-10 14:39:40 +02:00
net wifi: mac80211: fix integer overflow in hwmp_route_info_get() 2025-04-20 10:15:39 +02:00
rust rust: Fix enabling Rust and building with GCC for LoongArch 2025-04-10 14:39:36 +02:00
samples rust: treewide: switch to the kernel Vec type 2025-03-13 13:01:46 +01:00
scripts kbuild: deb-pkg: don't set KBUILD_BUILD_VERSION unconditionally 2025-04-10 14:39:35 +02:00
security smack: ipv4/ipv6: tcp/dccp/sctp: fix incorrect child socket label 2025-04-10 14:39:10 +02:00
sound ALSA: hda/realtek: Enable Mute LED on HP OMEN 16 Laptop xd000xx 2025-04-20 10:15:42 +02:00
tools ktest: Fix Test Failures Due to Missing LOG_FILE Directories 2025-04-20 10:15:27 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-13 13:02:18 +01:00
virt KVM: x86: switch hugepage recovery thread to vhost_task 2024-12-05 14:02:43 +01:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: enable Clippy's check-private-items 2025-03-13 13:01:42 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -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 self from DSA entry 2024-11-03 12:52:38 -08:00
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 MAINTAINERS: add entry for the Rust alloc module 2025-03-13 13:01:47 +01:00
Makefile Linux 6.12.23 2025-04-10 14:39:41 +02:00
README README: Fix spelling 2024-03-18 03:36:32 -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 reStructuredText 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.