CVE-2023-53323

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

ext2/dax: Fix ext2_setsize when len is page aligned

PAGE_ALIGN(x) macro gives the next highest value which is multiple of pagesize. But if x is already page aligned then it simply returns x. So, if x passed is 0 in dax_zero_range() function, that means the length gets passed as 0 to ->iomap_begin().

In ext2 it then calls ext2_get_blocks -> max_blocks as 0 and hits bug_on here in ext2_get_blocks(). BUG_ON(maxblocks == 0);

Instead we should be calling dax_truncate_page() here which takes care of it. i.e. it only calls dax_zero_range if the offset is not page/block aligned.

This can be easily triggered with following on fsdax mounted pmem device.

dd if=/dev/zero of=file count=1 bs=512 truncate -s 0 file

[79.525838] EXT2-fs (pmem0): DAX enabled. Warning: EXPERIMENTAL, use at your own risk [79.529376] ext2 filesystem being mounted at /mnt1/test supports timestamps until 2038 (0x7fffffff) [93.793207] ————[ cut here ]———— [93.795102] kernel BUG at fs/ext2/inode.c:637! [93.796904] invalid opcode: 0000 [#1] PREEMPT SMP PTI [93.798659] CPU: 0 PID: 1192 Comm: truncate Not tainted 6.3.0-rc2-xfstests-00056-g131086faa369 #139 [93.806459] RIP: 0010:ext2_get_blocks.constprop.0+0x524/0x610 <…> [93.835298] Call Trace: [93.836253] [93.837103] ? lock_acquire+0xf8/0x110 [93.838479] ? d_lookup+0x69/0xd0 [93.839779] ext2_iomap_begin+0xa7/0x1c0 [93.841154] iomap_iter+0xc7/0x150 [93.842425] dax_zero_range+0x6e/0xa0 [93.843813] ext2_setsize+0x176/0x1b0 [93.845164] ext2_setattr+0x151/0x200 [93.846467] notify_change+0x341/0x4e0 [93.847805] ? lock_acquire+0xf8/0x110 [93.849143] ? do_truncate+0x74/0xe0 [93.850452] ? do_truncate+0x84/0xe0 [93.851739] do_truncate+0x84/0xe0 [93.852974] do_sys_ftruncate+0x2b4/0x2f0 [93.854404] do_syscall_64+0x3f/0x90 [93.855789] entry_SYSCALL_64_after_hwframe+0x72/0xdc

Weakness

The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.

Affected Software

Extended Description

While assertion is good for catching logic errors and reducing the chances of reaching more serious vulnerability conditions, it can still lead to a denial of service. For example, if a server handles multiple simultaneous connections, and an assert() occurs in one single connection that causes all other connections to be dropped, this is a reachable assertion that leads to a denial of service.

Potential Mitigations

References

• https://git.kernel.org/stable/c/5cee8bfb8cbd99c97aff85d2bf066b6a496e13ab
• https://git.kernel.org/stable/c/9e54fd14bd143c261e52fde74355e85e9526c58c
• https://git.kernel.org/stable/c/fcced95b6ba2a507a83b8b3e0358a8ac16b13e35