Bug 2402240 (CVE-2022-50546)

Summary:	CVE-2022-50546 kernel: ext4: fix uninititialized value in 'ext4_evict_inode'
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	low	Docs Contact:
Priority:	low
Version:	unspecified	Keywords:	Security
Target Milestone:	---
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	An uninitialized variable flaw was found in the Linux kernel's ext4 filesystem in the inode eviction path. A local user can trigger this issue by creating filesystem operations that cause inode allocation to fail before the i_flags field is initialized, followed by inode cleanup that attempts to read the uninitialized field. This causes the kernel to access uninitialized memory, resulting in unpredictable behavior and denial of service through a kernel crash.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2025-10-07 16:04:54 UTC

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

ext4: fix uninititialized value in 'ext4_evict_inode'

Syzbot found the following issue:
=====================================================
BUG: KMSAN: uninit-value in ext4_evict_inode+0xdd/0x26b0 fs/ext4/inode.c:180
 ext4_evict_inode+0xdd/0x26b0 fs/ext4/inode.c:180
 evict+0x365/0x9a0 fs/inode.c:664
 iput_final fs/inode.c:1747 [inline]
 iput+0x985/0xdd0 fs/inode.c:1773
 __ext4_new_inode+0xe54/0x7ec0 fs/ext4/ialloc.c:1361
 ext4_mknod+0x376/0x840 fs/ext4/namei.c:2844
 vfs_mknod+0x79d/0x830 fs/namei.c:3914
 do_mknodat+0x47d/0xaa0
 __do_sys_mknodat fs/namei.c:3992 [inline]
 __se_sys_mknodat fs/namei.c:3989 [inline]
 __ia32_sys_mknodat+0xeb/0x150 fs/namei.c:3989
 do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
 __do_fast_syscall_32+0xa2/0x100 arch/x86/entry/common.c:178
 do_fast_syscall_32+0x33/0x70 arch/x86/entry/common.c:203
 do_SYSENTER_32+0x1b/0x20 arch/x86/entry/common.c:246
 entry_SYSENTER_compat_after_hwframe+0x70/0x82

Uninit was created at:
 __alloc_pages+0x9f1/0xe80 mm/page_alloc.c:5578
 alloc_pages+0xaae/0xd80 mm/mempolicy.c:2285
 alloc_slab_page mm/slub.c:1794 [inline]
 allocate_slab+0x1b5/0x1010 mm/slub.c:1939
 new_slab mm/slub.c:1992 [inline]
 ___slab_alloc+0x10c3/0x2d60 mm/slub.c:3180
 __slab_alloc mm/slub.c:3279 [inline]
 slab_alloc_node mm/slub.c:3364 [inline]
 slab_alloc mm/slub.c:3406 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3413 [inline]
 kmem_cache_alloc_lru+0x6f3/0xb30 mm/slub.c:3429
 alloc_inode_sb include/linux/fs.h:3117 [inline]
 ext4_alloc_inode+0x5f/0x860 fs/ext4/super.c:1321
 alloc_inode+0x83/0x440 fs/inode.c:259
 new_inode_pseudo fs/inode.c:1018 [inline]
 new_inode+0x3b/0x430 fs/inode.c:1046
 __ext4_new_inode+0x2a7/0x7ec0 fs/ext4/ialloc.c:959
 ext4_mkdir+0x4d5/0x1560 fs/ext4/namei.c:2992
 vfs_mkdir+0x62a/0x870 fs/namei.c:4035
 do_mkdirat+0x466/0x7b0 fs/namei.c:4060
 __do_sys_mkdirat fs/namei.c:4075 [inline]
 __se_sys_mkdirat fs/namei.c:4073 [inline]
 __ia32_sys_mkdirat+0xc4/0x120 fs/namei.c:4073
 do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
 __do_fast_syscall_32+0xa2/0x100 arch/x86/entry/common.c:178
 do_fast_syscall_32+0x33/0x70 arch/x86/entry/common.c:203
 do_SYSENTER_32+0x1b/0x20 arch/x86/entry/common.c:246
 entry_SYSENTER_compat_after_hwframe+0x70/0x82

CPU: 1 PID: 4625 Comm: syz-executor.2 Not tainted 6.1.0-rc4-syzkaller-62821-gcb231e2f67ec #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
=====================================================

Now, 'ext4_alloc_inode()' didn't init 'ei->i_flags'. If new inode failed
before set 'ei->i_flags' in '__ext4_new_inode()', then do 'iput()'. As after
6bc0d63dad7f commit will access 'ei->i_flags' in 'ext4_evict_inode()' which
will lead to access uninit-value.
To solve above issue just init 'ei->i_flags' in 'ext4_alloc_inode()'.

Comment 1 Jon Moroney 2025-10-07 17:14:38 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025100757-CVE-2022-50546-ef71@gregkh/T