Vulnerability CVE-2024-26720
Published: 2024-04-03

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

mm/writeback: fix possible divide-by-zero in wb_dirty_limits(), again

(struct dirty_throttle_control *)->thresh is an unsigned long, but is
passed as the u32 divisor argument to div_u64(). On architectures where
unsigned long is 64 bytes, the argument will be implicitly truncated.

Use div64_u64() instead of div_u64() so that the value used in the "is
this a safe division" check is the same as the divisor.

Also, remove redundant cast of the numerator to u64, as that should happen
implicitly.

This would be difficult to exploit in memcg domain, given the ratio-based
arithmetic domain_drity_limits() uses, but is much easier in global
writeback domain with a BDI_CAP_STRICTLIMIT-backing device, using e.g.
vm.dirty_bytes=(1<<32)*PAGE_SIZE so that dtc->thresh == (1<<32)

 References:
https://git.kernel.org/stable/c/c593d26fb5d577ef31b6e49a31e08ae3ebc1bc1e
https://git.kernel.org/stable/c/1f12e4b3284d6c863f272eb2de0d4248ed211cf4
https://git.kernel.org/stable/c/81e7d2530d458548b90a5c5e76b77ad5e5d1c0df
https://git.kernel.org/stable/c/5099871b370335809c0fd1abad74d9c7c205d43f
https://git.kernel.org/stable/c/16b1025eaa8fc223ab4273ece20d1c3a4211a95d
https://git.kernel.org/stable/c/ec18ec230301583395576915d274b407743d8f6c
https://git.kernel.org/stable/c/65977bed167a92e87085e757fffa5798f7314c9f
https://git.kernel.org/stable/c/9319b647902cbd5cc884ac08a8a6d54ce111fc78
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