AZL-68840

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

bpf: Explicitly check accesses to bpfsockaddr

Syzkaller found a kernel warning on the following sock_addr program:

0: r0 = 0
1: r2 = *(u32 *)(r1 +60)
2: exit

which triggers:

verifier bug: error during ctx access conversion (0)

This is happening because offset 60 in bpfsockaddr corresponds to an implicit padding of 4 bytes, right after msgsrcip4. Access to this padding isn't rejected in sockaddrisvalidaccess and it thus later fails to convert the access.

This patch fixes it by explicitly checking the various fields of bpfsockaddr in sockaddrisvalidaccess.

I checked the other ctx structures and isvalidaccess functions and didn't find any other similar cases. Other cases of (properly handled) padding are covered in new tests in a subsequent patch.