CVE-2022-49171

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

ext4: dont BUG if someone dirty pages without asking ext4 first

[un]pin_user_pages_remote is dirtying pages without properly warning the file system in advance. A related race was noted by Jan Kara in 2018[1]; however, more recently instead of it being a very hard-to-hit race, it could be reliably triggered by process_vm_writev(2) which was discovered by Syzbot[2].

This is technically a bug in mm/gup.c, but arguably ext4 is fragile in that if some other kernel subsystem dirty pages without properly notifying the file system using page_mkwrite(), ext4 will BUG, while other file systems will not BUG (although data will still be lost).

So instead of crashing with a BUG, issue a warning (since there may be potential data loss) and just mark the page as clean to avoid unprivileged denial of service attacks until the problem can be properly fixed. More discussion and background can be found in the thread starting at [2].

[1] https://lore.kernel.org/linux-mm/20180103100430.GE4911@quack2.suse.cz [2] https://lore.kernel.org/r/Yg0m6IjcNmfaSokM@google.com

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/0d3a6926f7e8be3c897fa46216ce13b119a9f56a
• https://git.kernel.org/stable/c/330d0e44fc5a47c27df958ecdd4693a3cb1d8b81
• https://git.kernel.org/stable/c/343117559ef41e992e326f7a92da1a8f254dfa8c
• https://git.kernel.org/stable/c/5a016c053f426a73752c3b41b60b497b58694d48
• https://git.kernel.org/stable/c/5db60e76edf5680ff1f3a7221036fc44b308f146
• https://git.kernel.org/stable/c/677c9d30e8487bee6c8e3b034070319d98f6e203
• https://git.kernel.org/stable/c/a0856764dc1276ad2dc7891288c2e9246bf11a37
• https://git.kernel.org/stable/c/cc5095747edfb054ca2068d01af20be3fcc3634f
• https://git.kernel.org/stable/c/d666dfaa571465a19f014534a214c255ea33f301