[PATCH] knfsd: clear both setuid and setgid whenever a chown is done

[Jeff Layton <jlayton@xxxxxxxxxx>]

Currently, knfsd only clears the setuid bit if the owner of a file
is changed on a SETATTR call, and only clears the setgid bit if
the group is changed. POSIX says this in the spec for chown():

    "If the specified file is a regular file, one or more of the
     S_IXUSR, S_IXGRP, or S_IXOTH bits of the file mode are set, and the
     process does not have appropriate privileges, the set-user-ID
     (S_ISUID) and set-group-ID (S_ISGID) bits of the file mode shall
     be cleared upon successful return from chown()."

If I'm reading this correct, then knfsd is doing this wrong. It should
be clearing both the setuid and setgid bit on any SETATTR that changes
the uid or gid. This wasn't really as noticable before, but now that the
ATTR_KILL_S*ID bits are a no-op for the NFS client, it's more evident.

This patch corrects the nfsd_setattr logic so that this occurs. It also
does a bit of cleanup to the function and eliminates an unneeded local
variable.

Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
 fs/nfsd/vfs.c |   30 ++++++++++++++----------------
 1 files changed, 14 insertions(+), 16 deletions(-)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 17ac51b..7d6cd1a 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -264,7 +264,6 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap,
 	struct inode	*inode;
 	int		accmode = MAY_SATTR;
 	int		ftype = 0;
-	int		imode;
 	__be32		err;
 	int		host_err;
 	int		size_change = 0;
@@ -360,25 +359,24 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap,
 		DQUOT_INIT(inode);
 	}
 
-	imode = inode->i_mode;
 	if (iap->ia_valid & ATTR_MODE) {
 		iap->ia_mode &= S_IALLUGO;
-		imode = iap->ia_mode |= (imode & ~S_IALLUGO);
-		/* if changing uid/gid revoke setuid/setgid in mode */
-		if ((iap->ia_valid & ATTR_UID) && iap->ia_uid != inode->i_uid) {
-			iap->ia_valid |= ATTR_KILL_PRIV;
+		iap->ia_mode |= (inode->i_mode & ~S_IALLUGO);
+	}
+
+	/* Revoke setuid/setgid on chown */
+	if (((iap->ia_valid & ATTR_UID) && iap->ia_uid != inode->i_uid) ||
+	    ((iap->ia_valid & ATTR_GID) && iap->ia_gid != inode->i_gid)) {
+		iap->ia_valid |= ATTR_KILL_PRIV;
+		if (iap->ia_valid & ATTR_MODE) {
+			/* we're setting mode too, just clear the mode bits */
 			iap->ia_mode &= ~S_ISUID;
+			if (iap->ia_mode & S_IXGRP)
+				iap->ia_mode &= ~S_ISGID;
+		} else {
+			/* set ATTR_KILL_* bits and let VFS handle it */
+			iap->ia_valid |= (ATTR_KILL_SUID | ATTR_KILL_SGID);
 		}
-		if ((iap->ia_valid & ATTR_GID) && iap->ia_gid != inode->i_gid)
-			iap->ia_mode &= ~S_ISGID;
-	} else {
-		/*
-		 * Revoke setuid/setgid bit on chown/chgrp
-		 */
-		if ((iap->ia_valid & ATTR_UID) && iap->ia_uid != inode->i_uid)
-			iap->ia_valid |= ATTR_KILL_SUID | ATTR_KILL_PRIV;
-		if ((iap->ia_valid & ATTR_GID) && iap->ia_gid != inode->i_gid)
-			iap->ia_valid |= ATTR_KILL_SGID;
 	}
 
 	/* Change the attributes. */
-- 
1.5.3.6

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