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Treat ACLs with extra ACEs for Admins and SYSTEM like a trivial ACL

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POSIX.1e requires that chmod changes the MASK rather than the
	GROUP_OBJ value if the ACL is non-trivial.

	On Windows, especially on home machines, a standard ACL often
	consists of entries for the user, maybe the group, and additional
	entries for SYSTEM and the Administrators group.  A user calling
	chmod on a file with bog standard Windows perms usually expects
	that chmod changes the GROUP_OBJ perms, but given the rules from
	POSIX.1e we can't do that.

	However, since we already treat Admins and SYSTEM special in a
	ACL (they are not used in MASK computations) we go a step in the
	Windows direction to follow user expectations.  If an ACL only
	consists of the three POSIX permissions, plus entries for Admins
	and SYSTEM *only*, then we change the permissions of the GROUP_OBJ
	entry *and* the MASK entry.

	* fhandler_disk_file.cc (fhandler_disk_file::chmod): Drop unused
	code.  Add special handling for a "standard" Windows ACL.  Add
	comment to explain.
	* sec_acl.cc (get_posix_access): Allow to return "standard-ness"
	of an ACL to the caller.  Add preceeding comment to explain a bit.
	* security.h (get_posix_access): Align prototype.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen
2016-01-28 22:05:49 +01:00
parent a16ab1751c
commit ac4648c13e
3 changed files with 30 additions and 20 deletions
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30
winsup/cygwin/fhandler_disk_file.cc
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@@ -787,35 +787,35 @@ fhandler_disk_file::fchmod (mode_t mode)
gid_t gid;
tmp_pathbuf tp;
aclent_t *aclp;
bool standard_acl = false;
int nentries, idx;
if (!get_file_sd (get_handle (), pc, sd, false))
{
aclp = (aclent_t *) tp.c_get ();
if ((nentries = get_posix_access (sd, NULL, &uid, &gid,
aclp, MAX_ACL_ENTRIES)) >= 0)
aclp, MAX_ACL_ENTRIES,
&standard_acl)) >= 0)
{
/* Overwrite ACL permissions as required by POSIX 1003.1e
draft 17. */
aclp[0].a_perm = (mode >> 6) & S_IRWXO;
#if 0
/* Deliberate deviation from POSIX 1003.1e here. We're not
writing CLASS_OBJ *or* GROUP_OBJ, but both. Otherwise we're
going to be in constant trouble with user expectations. */
if ((idx = searchace (aclp, nentries, GROUP_OBJ)) >= 0)
aclp[idx].a_perm = (mode >> 3) & S_IRWXO;
if (nentries > MIN_ACL_ENTRIES
&& (idx = searchace (aclp, nentries, CLASS_OBJ)) >= 0)
aclp[idx].a_perm = (mode >> 3) & S_IRWXO;
#else
/* POSIXly correct: If CLASS_OBJ is present, chmod only modifies
CLASS_OBJ, not GROUP_OBJ. */
CLASS_OBJ, not GROUP_OBJ.
Deliberate deviation from POSIX 1003.1e: If the ACL is a
"standard" ACL, that is, it only contains POSIX permissions
as well as entries for the Administrators group and SYSTEM,
then it's kind of a POSIX-only ACL in a twisted, Windowsy
way. If so, we change GROUP_OBJ and CLASS_OBJ perms. */
if (standard_acl
&& (idx = searchace (aclp, nentries, GROUP_OBJ)) >= 0)
aclp[idx].a_perm = (mode >> 3) & S_IRWXO;
if (nentries > MIN_ACL_ENTRIES
&& (idx = searchace (aclp, nentries, CLASS_OBJ)) >= 0)
aclp[idx].a_perm = (mode >> 3) & S_IRWXO;
else if ((idx = searchace (aclp, nentries, GROUP_OBJ)) >= 0)
aclp[idx].a_perm = (mode >> 3) & S_IRWXO;
#endif
if ((idx = searchace (aclp, nentries, OTHER_OBJ)) >= 0)
aclp[idx].a_perm = mode & S_IRWXO;
if (pc.isdir ())