linux-cve-announce - CVE-2025-68796: f2fs: fix to avoid updating zero-sized extent in extent cache

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Message-ID: <2026011306-CVE-2025-68796-9eee@gregkh>
Date: Tue, 13 Jan 2026 16:29:22 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-68796: f2fs: fix to avoid updating zero-sized extent in extent cache

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

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

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

f2fs: fix to avoid updating zero-sized extent in extent cache

As syzbot reported:

F2FS-fs (loop0): __update_extent_tree_range: extent len is zero, type: 0, extent [0, 0, 0], age [0, 0]
------------[ cut here ]------------
kernel BUG at fs/f2fs/extent_cache.c:678!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5336 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:__update_extent_tree_range+0x13bc/0x1500 fs/f2fs/extent_cache.c:678
Call Trace:
 <TASK>
 f2fs_update_read_extent_cache_range+0x192/0x3e0 fs/f2fs/extent_cache.c:1085
 f2fs_do_zero_range fs/f2fs/file.c:1657 [inline]
 f2fs_zero_range+0x10c1/0x1580 fs/f2fs/file.c:1737
 f2fs_fallocate+0x583/0x990 fs/f2fs/file.c:2030
 vfs_fallocate+0x669/0x7e0 fs/open.c:342
 ioctl_preallocate fs/ioctl.c:289 [inline]
 file_ioctl+0x611/0x780 fs/ioctl.c:-1
 do_vfs_ioctl+0xb33/0x1430 fs/ioctl.c:576
 __do_sys_ioctl fs/ioctl.c:595 [inline]
 __se_sys_ioctl+0x82/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f07bc58eec9

In error path of f2fs_zero_range(), it may add a zero-sized extent
into extent cache, it should be avoided.

The Linux kernel CVE team has assigned CVE-2025-68796 to this issue.


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

	Issue introduced in 4.7 with commit 6e9619499f53b22ead972e476c0e8341c997d929 and fixed in 6.1.160 with commit e50b81c50fcbe63f50405bb40f262162ff32af88
	Issue introduced in 4.7 with commit 6e9619499f53b22ead972e476c0e8341c997d929 and fixed in 6.6.120 with commit efe3371001f50a2d6f746b50bdc6f9f26b2089ec
	Issue introduced in 4.7 with commit 6e9619499f53b22ead972e476c0e8341c997d929 and fixed in 6.12.64 with commit 4f244c64efe628d277b916f47071adf480eb8646
	Issue introduced in 4.7 with commit 6e9619499f53b22ead972e476c0e8341c997d929 and fixed in 6.18.3 with commit bac23833220a1f8fe8dfab7e16efa20ff64d7589
	Issue introduced in 4.7 with commit 6e9619499f53b22ead972e476c0e8341c997d929 and fixed in 6.19-rc1 with commit 7c37c79510329cd951a4dedf3f7bf7e2b18dccec

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-2025-68796
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/f2fs/file.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/e50b81c50fcbe63f50405bb40f262162ff32af88
	https://git.kernel.org/stable/c/efe3371001f50a2d6f746b50bdc6f9f26b2089ec
	https://git.kernel.org/stable/c/4f244c64efe628d277b916f47071adf480eb8646
	https://git.kernel.org/stable/c/bac23833220a1f8fe8dfab7e16efa20ff64d7589
	https://git.kernel.org/stable/c/7c37c79510329cd951a4dedf3f7bf7e2b18dccec