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Block writes to /proc/self/exe and /proc/self/map_files #36

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Expand Up @@ -629,6 +629,22 @@ tells userspace that there was an fd, but it was not allowed through.

**Use-Case:** Any code that wants to use `SCM_RIGHTS` properly.

### Block reopening R/O file descriptor for /proc/self/exe and /proc/self/map_files/*

Provide a security primitive that prevents processes from reopening a
read-only file descriptor to `/proc/self/exe` and files under
`/proc/self/map_files`. This directly addresses the attack vector used
in CVE-2019-5736.

A common workaround used by container runtimes to prevent an untrusted
container process from overwriting the host's runtime executable is to
"re-exec" themselves from a read-only copy of the binary.

While this looks like a kernel issue, the assumption is still that any
container runtime must ensure its binary cannot be overwritten.

**Use-Case:** Any container runtime that executes an untrusted executable.

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## Finished Items
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