K 10
svn:author
V 6
kevans
K 8
svn:date
V 27
2020-04-14T13:32:03.179858Z
K 7
svn:log
V 546
posixshm: fix counting of writable mappings

Similar to mmap'ing vnodes, posixshm should count any mapping where maxprot
contains VM_PROT_WRITE (i.e. fd opened r/w with no write-seal applied) as
writable and thus blocking of any write-seal.

The memfd tests have been amended to reflect the fixes here, which notably
includes:

1. Fix for error return bug; EPERM is not a documented failure mode for mmap
2. Fix rejection of write-seal with active mappings that can be upgraded via
    mprotect(2).

Reported by:	markj
Discussed with:	markj, kib

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