Fix CVE-2017-5669: shm shmat mmap nil-page protection #114
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Background
In ipc/shm.c, do_shmat() can call mmap with MAP_FIXED to address 0 when attaching a shared memory segment, but the nil-page (addr == 0) is not properly protected; this can lead to incorrect memory mappings and potential local denial-of-service or security policy bypass (CVE-2017-5669).:contentReference[oaicite:1]{index=1}
Changes
Harden shmat() by adjusting address rounding and nil-page handling so that mappings to address 0 respect nil-page protection and do not result in an unsafe MAP_FIXED nil mapping.:contentReference[oaicite:2]{index=2}
Security Impact
Prevents local processes from exploiting the shared memory attach path to map nil-page under unsafe conditions, addressing CVE-2017-5669.:contentReference[oaicite:3]{index=3}
References
Upstream commit: e1d35d4dc7f089e6c9c080d556feedf9c706f0c7; CVE: CVE-2017-5669