Linux kernel: BPF verifier bug leads to out-of-bounds access (CVE-2018-18445; 4.14.9-4.14.74; 4.15-4.18.12)

[Jann Horn <jannh () google com>]

NOTE: I have requested a CVE identifier, and I'm sending this message,
to make tracking of the fix easier; however, to avoid missing security
fixes without CVE identifiers, you should *NOT* be cherry-picking a
specific patch in response to a notification about a kernel security
bug.

In Linux kernel versions 4.14.9-4.14.74 and 4.15-4.18.12, faulty
computation of numeric bounds in the BPF verifier permits
out-of-bounds memory accesses because adjust_scalar_min_max_vals in
kernel/bpf/verifier.c mishandles 32-bit right shifts. 4.18.13 and
4.14.75 are fixed.

This is CVE-2018-18445.

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=b799207e1e1816b09e7a5920fbb2d5fcf6edd681
https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.18.13
https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.14.75
https://bugs.chromium.org/p/project-zero/issues/detail?id=1686