faccessat has at least two, and probably three bugs.
First, a typo - the EINVAL check is done against flags (the fourth argument)
rather than mode (third argument), such that faccessat(AT_FDCWD,".",-1,0)
passes even though the corresponding access(".",-1) fails.
Second, it is not performing the proper checks when AT_EACCESS is set and the
applications' effective id differs from the real id (to fix this would require
adding a parameter to fhandler_base::fhaccess). If this latter bug is fixed,
then it would be nice to copy Linux and export:
euidaccess(file,mode) => faccessat(AT_FDCWD,file,mode,AT_EACCESS)
eaccess(file,mode) => euidaccess(file,mode)
Third, POSIX permits us to return EINVAL to reject flags we don't support. For
example, both:
faccessat(fd,name,F_OK,AT_REMOVEDIR)
fchownat(fd,name,uid,gid,AT_EACCESS)
should probably fail with EINVAL. In other words, we should support only the
following:
faccessat - AT_SYMLINK_NOFOLLOW, AT_EACCESS (POSIX doesn't require
AT_SYMLINK_NOFOLLOW, but Linux supports it)
fchownat, fchmodat, fstatat, utimensat - AT_SYMLINK_NOFOLLOW
linkat - AT_SYMLINK_FOLLOW
unlinkat - AT_REMOVEDIR
--
Eric Blake
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