Message-ID: <2025050127-CVE-2025-23150-15b8@gregkh>
Date: Thu,  1 May 2025 14:56:30 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-23150: ext4: fix off-by-one error in do_split

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

ext4: fix off-by-one error in do_split

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.

The Linux kernel CVE team has assigned CVE-2025-23150 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.9 with commit 5872331b3d91820e14716632ebb56b1399b34fe1 and fixed in 6.1.135 with commit 35d0aa6db9d93307085871ceab8a729594a98162
	Issue introduced in 5.9 with commit 5872331b3d91820e14716632ebb56b1399b34fe1 and fixed in 6.6.88 with commit 2eeb1085bf7bd5c7ba796ca4119925fa5d336a3f
	Issue introduced in 5.9 with commit 5872331b3d91820e14716632ebb56b1399b34fe1 and fixed in 6.12.24 with commit 16d9067f00e3a7d1df7c3aa9c20d214923d27e10
	Issue introduced in 5.9 with commit 5872331b3d91820e14716632ebb56b1399b34fe1 and fixed in 6.13.12 with commit 17df39f455f1289319d4d09e4826aa46852ffd17
	Issue introduced in 5.9 with commit 5872331b3d91820e14716632ebb56b1399b34fe1 and fixed in 6.14.3 with commit ab0cc5c25552ae0d20eae94b40a93be11b080fc5
	Issue introduced in 5.9 with commit 5872331b3d91820e14716632ebb56b1399b34fe1 and fixed in 6.15-rc2 with commit 94824ac9a8aaf2fb3c54b4bdde842db80ffa555d
	Issue introduced in 4.4.234 with commit 059b1480105478c5f68cf664301545b8cad6a7cf
	Issue introduced in 4.9.234 with commit 539ae3e03875dacaa9c388aff141ccbb4ef4ecb5
	Issue introduced in 4.14.195 with commit fbbfd55a40d5d0806b59ee0403c75d5ac517533f
	Issue introduced in 4.19.142 with commit b3ddf6ba5e28a57729fff1605ae08e21be5c92e3
	Issue introduced in 5.4.61 with commit ea54176e5821936d109bb45dc2c19bd53559e735
	Issue introduced in 5.7.18 with commit e50fe43e3062e18846e99d9646b9c07b097eb1ed
	Issue introduced in 5.8.4 with commit 88e79f7a9841278fa8ff7ff6178bad12da002ffc

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-23150
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/ext4/namei.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/35d0aa6db9d93307085871ceab8a729594a98162
	https://git.kernel.org/stable/c/2eeb1085bf7bd5c7ba796ca4119925fa5d336a3f
	https://git.kernel.org/stable/c/16d9067f00e3a7d1df7c3aa9c20d214923d27e10
	https://git.kernel.org/stable/c/17df39f455f1289319d4d09e4826aa46852ffd17
	https://git.kernel.org/stable/c/ab0cc5c25552ae0d20eae94b40a93be11b080fc5
	https://git.kernel.org/stable/c/94824ac9a8aaf2fb3c54b4bdde842db80ffa555d

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