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() didnt 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().

Weakness

The product uses or accesses a resource that has not been initialized.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/091f85db4c3fb1734a6d7fb4777a2b2831da6631
• https://git.kernel.org/stable/c/3c31d8d3ad95aef8cc17a4fcf317e46217148439
• https://git.kernel.org/stable/c/56491d60ddca9c697d885394cb0173675b9ab81f
• https://git.kernel.org/stable/c/7ea71af94eaaaf6d9aed24bc94a05b977a741cb9
• https://git.kernel.org/stable/c/9f966e021c20caae639dd0e404c8761e8281a2c4
• https://git.kernel.org/stable/c/e431b4fb1fb8c2654b808086e9747a000adb9655
• https://git.kernel.org/stable/c/f0bffdcc7cb14598af2aa706f1e0f2a9054154ba