shmfd/mmap: restrict maxprot with MAP_SHARED + F_SEAL_WRITE
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Authored by kevans on Dec 30 2019, 10:58 PM.

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rS356371: shmfd/mmap: restrict maxprot with MAP_SHARED + F_SEAL_WRITE

Summary

If a write seal is set on a shared mapping, we must exclude VM_PROT_WRITE as the fd is effectively read-only. This was discovered by running devel/linux-ltp, which mmap's with acceptable protections specified then attempts to raise to PROT_READ|PROT_WRITE with mprotect(2), which we allowed.