Re: [Patch 1/2] selinux: ajust rules for ATTR_FORCE

[OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>]

OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> writes:

>>> > ATTR_FORCE is supposed to suppress permission checking altogether, and
>>> > shouldn't be mixed with multiple attribute changes if some should be
>>> > subject to permission checks while others should not.
>>> 
>>> I disagree. In fact, ATTR_FORCE is just used for ATTR_KILL_S[UG]ID, and
>>> notify_change() is disallowing the mixed ATTR_MODE and ATTR_KILL_*. I
>>> think it should be enough.
>>
>> Ok, then we just need to adjust selinux_inode_setattr to understand that
>> ATTR_FORCE only means to bypass checking on ATTR_MODE.
>
> Ok, sure. I'll try it.

Could you review this? I've added ATTR_TIMES_SET to check explicit
utimes(), and tried it with minimum change.

[I'm not sure this handles notify_change() usage of nfsd (and perhaps
other network fs too) correctly, and whether selinux may want to check
it. I guess network fs _may_ try to change the multiple attributes at a
time. Well, even if it's true, it would be another topic...]

Thanks.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>


From: Amerigo Wang <amwang@redhat.com>

As suggested by OGAWA Hirofumi in thread: http://lkml.org/lkml/2009/8/7/132,
we should let selinux_inode_setattr() to match our ATTR_* rules.
ATTR_FORCE should not force things like ATTR_SIZE.

Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Eric Paris <eparis@redhat.com>
Signed-off-by: WANG Cong <amwang@redhat.com>
[tweaks]
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
---

 security/selinux/hooks.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff -puN security/selinux/hooks.c~selinux-truncate-fix security/selinux/hooks.c
--- linux-2.6/security/selinux/hooks.c~selinux-truncate-fix	2009-08-18 03:50:09.000000000 +0900
+++ linux-2.6-hirofumi/security/selinux/hooks.c	2009-08-18 05:35:11.000000000 +0900
@@ -2711,12 +2711,17 @@ static int selinux_inode_permission(stru
 static int selinux_inode_setattr(struct dentry *dentry, struct iattr *iattr)
 {
 	const struct cred *cred = current_cred();
+	unsigned int ia_valid = iattr->ia_valid;
 
-	if (iattr->ia_valid & ATTR_FORCE)
-		return 0;
+	/* ATTR_FORCE is just used for ATTR_KILL_S[UG]ID. */
+	if (ia_valid & ATTR_FORCE) {
+		ia_valid &= ~(ATTR_KILL_SUID | ATTR_KILL_SGID | ATTR_MODE);
+		if (!ia_valid)
+			return 0;
+	}
 
-	if (iattr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID |
-			       ATTR_ATIME_SET | ATTR_MTIME_SET))
+	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID |
+			ATTR_ATIME_SET | ATTR_MTIME_SET | ATTR_TIMES_SET))
 		return dentry_has_perm(cred, NULL, dentry, FILE__SETATTR);
 
 	return dentry_has_perm(cred, NULL, dentry, FILE__WRITE);
_