[PATCH 3/3] use inode_change_ok for setattr permission checking

[Christoph Hellwig <hch@infradead.org>]

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Instead of implementing our own checks use inode_change_ok to check for
nessecary permission in setattr.  There is a slight change in behaviour
as inode_change_ok doesn't allow i_mode updates to add the suid or sgid
without superuser privilegues while the old XFS code just stripped away
those bits from the file mode.

(First sent on Semptember 29th)


Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: linux-2.6-xfs/fs/xfs/xfs_vnodeops.c
===================================================================
--- linux-2.6-xfs.orig/fs/xfs/xfs_vnodeops.c	2008-10-03 22:16:03.000000000 +0200
+++ linux-2.6-xfs/fs/xfs/xfs_vnodeops.c	2008-10-03 22:16:32.000000000 +0200
@@ -70,7 +70,6 @@ xfs_setattr(
 	gid_t			gid=0, igid=0;
 	int			timeflags = 0;
 	struct xfs_dquot	*udqp, *gdqp, *olddquot1, *olddquot2;
-	int			file_owner;
 	int			need_iolock = 1;
 
 	xfs_itrace_entry(ip);
@@ -81,6 +80,10 @@ xfs_setattr(
 	if (XFS_FORCED_SHUTDOWN(mp))
 		return XFS_ERROR(EIO);
 
+	code = -inode_change_ok(inode, iattr);
+	if (code)
+		return code;
+
 	olddquot1 = olddquot2 = NULL;
 	udqp = gdqp = NULL;
 
@@ -158,56 +161,6 @@ xfs_setattr(
 
 	xfs_ilock(ip, lock_flags);
 
-	/* boolean: are we the file owner? */
-	file_owner = (current_fsuid() == ip->i_d.di_uid);
-
-	/*
-	 * Change various properties of a file.
-	 * Only the owner or users with CAP_FOWNER
-	 * capability may do these things.
-	 */
-	if (mask & (ATTR_MODE|ATTR_UID|ATTR_GID)) {
-		/*
-		 * CAP_FOWNER overrides the following restrictions:
-		 *
-		 * The user ID of the calling process must be equal
-		 * to the file owner ID, except in cases where the
-		 * CAP_FSETID capability is applicable.
-		 */
-		if (!file_owner && !capable(CAP_FOWNER)) {
-			code = XFS_ERROR(EPERM);
-			goto error_return;
-		}
-
-		/*
-		 * CAP_FSETID overrides the following restrictions:
-		 *
-		 * The effective user ID of the calling process shall match
-		 * the file owner when setting the set-user-ID and
-		 * set-group-ID bits on that file.
-		 *
-		 * The effective group ID or one of the supplementary group
-		 * IDs of the calling process shall match the group owner of
-		 * the file when setting the set-group-ID bit on that file
-		 */
-		if (mask & ATTR_MODE) {
-			mode_t m = 0;
-
-			if ((iattr->ia_mode & S_ISUID) && !file_owner)
-				m |= S_ISUID;
-			if ((iattr->ia_mode & S_ISGID) &&
-			    !in_group_p((gid_t)ip->i_d.di_gid))
-				m |= S_ISGID;
-#if 0
-			/* Linux allows this, Irix doesn't. */
-			if ((iattr->ia_mode & S_ISVTX) && !S_ISDIR(ip->i_d.di_mode))
-				m |= S_ISVTX;
-#endif
-			if (m && !capable(CAP_FSETID))
-				iattr->ia_mode &= ~m;
-		}
-	}
-
 	/*
 	 * Change file ownership.  Must be the owner or privileged.
 	 */
@@ -224,22 +177,6 @@ xfs_setattr(
 		uid = (mask & ATTR_UID) ? iattr->ia_uid : iuid;
 
 		/*
-		 * CAP_CHOWN overrides the following restrictions:
-		 *
-		 * If _POSIX_CHOWN_RESTRICTED is defined, this capability
-		 * shall override the restriction that a process cannot
-		 * change the user ID of a file it owns and the restriction
-		 * that the group ID supplied to the chown() function
-		 * shall be equal to either the group ID or one of the
-		 * supplementary group IDs of the calling process.
-		 */
-		if ((iuid != uid ||
-		     (igid != gid && !in_group_p((gid_t)gid))) &&
-		    !capable(CAP_CHOWN)) {
-			code = XFS_ERROR(EPERM);
-			goto error_return;
-		}
-		/*
 		 * Do a quota reservation only if uid/gid is actually
 		 * going to change.
 		 */
@@ -284,19 +221,6 @@ xfs_setattr(
 	}
 
 	/*
-	 * Change file access or modified times.
-	 */
-	if (mask & (ATTR_ATIME|ATTR_MTIME)) {
-		if (!file_owner) {
-			if ((mask & (ATTR_MTIME_SET|ATTR_ATIME_SET)) &&
-			    !capable(CAP_FOWNER)) {
-				code = XFS_ERROR(EPERM);
-				goto error_return;
-			}
-		}
-	}
-
-	/*
 	 * Now we can make the changes.  Before we join the inode
 	 * to the transaction, if ATTR_SIZE is set then take care of
 	 * the part of the truncation that must be done without the

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