bpf: Fix hashtab overflow check on 32-bit arches

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix hashtab overflow check on 32-bit arches The hashtab code relies on roundup_pow_of_two() to compute the number of hash buckets, and contains an overflow check by checking if the resulting value is 0. However, on 32-bit arches, the roundup code itself can overflow by doing a 32-bit left-shift of an unsigned long value, which is undefined behaviour, so it is not guaranteed to truncate neatly. This was triggered by syzbot on the DEVMAP_HASH type, which contains the same check, copied from the hashtab code. So apply the same fix to hashtab, by moving the overflow check to before the roundup.

References

• https://git.kernel.org/stable/c/33ec04cadb77605b71d9298311919303d390c4d5
• https://git.kernel.org/stable/c/92c81fbb3ed2e0dfc33a4183a67135e1ab566ace
• https://git.kernel.org/stable/c/64f00b4df0597590b199b62a37a165473bf658a6
• https://git.kernel.org/stable/c/3b08cfc65f07b1132c1979d73f014ae6e04de55d
• https://git.kernel.org/stable/c/a83fdaeaea3677b83a53f72ace2d73a19bcd6d93
• https://git.kernel.org/stable/c/8435f0961bf3dc65e204094349bd9aeaac1f8868
• https://git.kernel.org/stable/c/d817f0d34d927f2deb17dadbfe212c9a6a32ac3e
• https://git.kernel.org/stable/c/a6fa75b5096c0f9826a4fabe22d907b0a5bb1016
• https://git.kernel.org/stable/c/6787d916c2cf9850c97a0a3f73e08c43e7d973b1