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ext2: reject inodes with zero i_nlink and valid mode in ext2_iget()

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ext2_iget() already rejects inodes with i_nlink == 0 when i_mode is
zero or i_dtime is set, treating them as deleted. However, the case of
i_nlink == 0 with a non-zero mode and zero dtime slips through. Since
ext2 has no orphan list, such a combination can only result from
filesystem corruption - a legitimate inode deletion always sets either
i_dtime or clears i_mode before freeing the inode.

A crafted image can exploit this gap to present such an inode to the
VFS, which then triggers WARN_ON inside drop_nlink() (fs/inode.c) via
ext2_unlink(), ext2_rename() and ext2_rmdir():

WARNING: CPU: 3 PID: 609 at fs/inode.c:336 drop_nlink+0xad/0xd0 fs/inode.c:336
CPU: 3 UID: 0 PID: 609 Comm: syz-executor Not tainted 6.12.77+ #1
Call Trace:
 <TASK>
 inode_dec_link_count include/linux/fs.h:2518 [inline]
 ext2_unlink+0x26c/0x300 fs/ext2/namei.c:295
 vfs_unlink+0x2fc/0x9b0 fs/namei.c:4477
 do_unlinkat+0x53e/0x730 fs/namei.c:4541
 __x64_sys_unlink+0xc6/0x110 fs/namei.c:4587
 do_syscall_64+0xf5/0x220 arch/x86/entry/common.c:78
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
 </TASK>

WARNING: CPU: 0 PID: 646 at fs/inode.c:336 drop_nlink+0xad/0xd0 fs/inode.c:336
CPU: 0 UID: 0 PID: 646 Comm: syz.0.17 Not tainted 6.12.77+ #1
Call Trace:
 <TASK>
 inode_dec_link_count include/linux/fs.h:2518 [inline]
 ext2_rename+0x35e/0x850 fs/ext2/namei.c:374
 vfs_rename+0xf2f/0x2060 fs/namei.c:5021
 do_renameat2+0xbe2/0xd50 fs/namei.c:5178
 __x64_sys_rename+0x7e/0xa0 fs/namei.c:5223
 do_syscall_64+0xf5/0x220 arch/x86/entry/common.c:78
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
 </TASK>

WARNING: CPU: 0 PID: 634 at fs/inode.c:336 drop_nlink+0xad/0xd0 fs/inode.c:336
CPU: 0 UID: 0 PID: 634 Comm: syz-executor Not tainted 6.12.77+ #1
Call Trace:
 <TASK>
 inode_dec_link_count include/linux/fs.h:2518 [inline]
 ext2_rmdir+0xca/0x110 fs/ext2/namei.c:311
 vfs_rmdir+0x204/0x690 fs/namei.c:4348
 do_rmdir+0x372/0x3e0 fs/namei.c:4407
 __x64_sys_unlinkat+0xf0/0x130 fs/namei.c:4577
 do_syscall_64+0xf5/0x220 arch/x86/entry/common.c:78
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
 </TASK>

Extend the existing i_nlink == 0 check to also catch this case,
reporting the corruption via ext2_error() and returning -EFSCORRUPTED.
This rejects the inode at load time and prevents it from reaching any
of the namei.c paths.

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

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Vasiliy Kovalev <kovalev@altlinux.org>
Link: https://patch.msgid.link/20260404152011.2590197-1-kovalev@altlinux.org
Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Vasiliy Kovalev
2026-04-04 18:20:11 +03:00
committed by Jan Kara
parent 9829995382
commit 25947cc5b2
1 changed files with 11 additions and 3 deletions
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14
fs/ext2/inode.c
View File

@@ -1431,9 +1431,17 @@ struct inode *ext2_iget (struct super_block *sb, unsigned long ino)
* the test is that same one that e2fsck uses
* NeilBrown 1999oct15
*/
if (inode->i_nlink == 0 && (inode->i_mode == 0 || ei->i_dtime)) {
/* this inode is deleted */
ret = -ESTALE;
if (inode->i_nlink == 0) {
if (inode->i_mode == 0 || ei->i_dtime) {
/* this inode is deleted */
ret = -ESTALE;
} else {
ext2_error(sb, __func__,
"inode %lu has zero i_nlink with mode 0%o and no dtime, "
"filesystem may be corrupt",
ino, inode->i_mode);
ret = -EFSCORRUPTED;
}
goto bad_inode;
}
inode->i_blocks = le32_to_cpu(raw_inode->i_blocks);