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

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
View File

@ -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 ())

16
winsup/cygwin/sec_acl.cc
View File

@ -561,11 +561,17 @@ getace (aclent_t &acl, int type, int id, DWORD win_ace_mask,
/* From the SECURITY_DESCRIPTOR given in psd, compute user, owner, posix
attributes, as well as the POSIX acl. The function returns the number
of entries returned in aclbufp, or -1 in case of error. */
of entries returned in aclbufp, or -1 in case of error.
When called from chmod, it also returns the fact if the ACL is a "standard"
ACL. A "standard" ACL is an ACL which only consists of ACEs for owner,
group, other, as well as (this is Windows) the Administrators group and
SYSTEM. See fhandler_disk_file::fchmod for how this is used to fake
stock POSIX perms even if Administrators and SYSTEM is in the ACE. */
int
get_posix_access (PSECURITY_DESCRIPTOR psd,
mode_t *attr_ret, uid_t *uid_ret, gid_t *gid_ret,
aclent_t *aclbufp, int nentries)
aclent_t *aclbufp, int nentries, bool *std_acl)
{
tmp_pathbuf tp;
NTSTATUS status;
@ -852,7 +858,10 @@ get_posix_access (PSECURITY_DESCRIPTOR psd,
GROUP_OBJ entry. */
if (ace_sid != well_known_system_sid
&& ace_sid != well_known_admins_sid)
{
class_perm |= lacl[pos].a_perm;
standard_ACEs_only = false;
}
}
}
/* For a newly created file, we'd like to know if we're running
@ -861,7 +870,6 @@ get_posix_access (PSECURITY_DESCRIPTOR psd,
a standard ACL, we apply umask. That's not entirely correct,
but it's probably the best we can do. */
else if (type & (USER | GROUP)
&& just_created
&& standard_ACEs_only
&& ace_sid != well_known_system_sid
&& ace_sid != well_known_admins_sid)
@ -1104,6 +1112,8 @@ out:
aclbufp[idx].a_perm &= S_IRWXO;
aclsort32 (pos, 0, aclbufp);
}
if (std_acl)
*std_acl = standard_ACEs_only;
return pos;
}

2
winsup/cygwin/security.h
View File

@ -467,7 +467,7 @@ int searchace (struct acl *, int, int, uid_t id = ILLEGAL_UID);
PSECURITY_DESCRIPTOR set_posix_access (mode_t, uid_t, gid_t, struct acl *, int,
security_descriptor &, bool);
int get_posix_access (PSECURITY_DESCRIPTOR, mode_t *, uid_t *, gid_t *,
struct acl *, int);
struct acl *, int, bool * = NULL);
int getacl (HANDLE, path_conv &, int, struct acl *);
int setacl (HANDLE, path_conv &, int, struct acl *, bool &);