locks,lockd: fix race in nlmsvc_testlock

posix_test_lock() returns a pointer to a struct file_lock which is unprotected
and can be removed while in use by the caller.  Move the conflicting lock from
the return to a parameter, and copy the conflicting lock.

In most cases the caller ends up putting the copy of the conflicting lock on
the stack.  On i386, sizeof(struct file_lock) appears to be about 100 bytes.
We're assuming that's reasonable.
Signed-off-by: Andy Adamson <andros@citi.umich.edu>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/lockd/svclock.c

@@ -376,8 +376,6 @@ u32
 nlmsvc_testlock(struct nlm_file *file, struct nlm_lock *lock,
 				       struct nlm_lock *conflock)
 {
-	struct file_lock	*fl;
-
 	dprintk("lockd: nlmsvc_testlock(%s/%ld, ty=%d, %Ld-%Ld)\n",
 				file->f_file->f_dentry->d_inode->i_sb->s_id,
 				file->f_file->f_dentry->d_inode->i_ino,
@@ -385,14 +383,14 @@ nlmsvc_testlock(struct nlm_file *file, struct nlm_lock *lock,
 				(long long)lock->fl.fl_start,
 				(long long)lock->fl.fl_end);
 
-	if ((fl = posix_test_lock(file->f_file, &lock->fl)) != NULL) {
+	if (posix_test_lock(file->f_file, &lock->fl, &conflock->fl)) {
 		dprintk("lockd: conflicting lock(ty=%d, %Ld-%Ld)\n",
-				fl->fl_type, (long long)fl->fl_start,
-				(long long)fl->fl_end);
+				conflock->fl.fl_type,
+				(long long)conflock->fl.fl_start,
+				(long long)conflock->fl.fl_end);
 		conflock->caller = "somehost";	/* FIXME */
 		conflock->oh.len = 0;		/* don't return OH info */
-		conflock->svid = fl->fl_pid;
-		conflock->fl = *fl;
+		conflock->svid = conflock->fl.fl_pid;
 		return nlm_lck_denied;
 	}
 

fs/locks.c

@@ -672,8 +672,9 @@ static int locks_block_on_timeout(struct file_lock *blocker, struct file_lock *w
 	return result;
 }
 
-struct file_lock *
-posix_test_lock(struct file *filp, struct file_lock *fl)
+int
+posix_test_lock(struct file *filp, struct file_lock *fl,
+		struct file_lock *conflock)
 {
 	struct file_lock *cfl;
 
@@ -684,9 +685,13 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
 		if (posix_locks_conflict(cfl, fl))
 			break;
 	}
+	if (cfl) {
+		locks_copy_lock(conflock, cfl);
+		unlock_kernel();
+		return 1;
+	}
 	unlock_kernel();
-
-	return (cfl);
+	return 0;
 }
 
 EXPORT_SYMBOL(posix_test_lock);
@@ -1563,7 +1568,7 @@ asmlinkage long sys_flock(unsigned int fd, unsigned int cmd)
  */
 int fcntl_getlk(struct file *filp, struct flock __user *l)
 {
-	struct file_lock *fl, file_lock;
+	struct file_lock *fl, cfl, file_lock;
 	struct flock flock;
 	int error;
 
@@ -1587,7 +1592,7 @@ int fcntl_getlk(struct file *filp, struct flock __user *l)
 		else
 		  fl = (file_lock.fl_type == F_UNLCK ? NULL : &file_lock);
 	} else {
-		fl = posix_test_lock(filp, &file_lock);
+		fl = (posix_test_lock(filp, &file_lock, &cfl) ? &cfl : NULL);
 	}
  
 	flock.l_type = F_UNLCK;
@@ -1717,7 +1722,7 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
  */
 int fcntl_getlk64(struct file *filp, struct flock64 __user *l)
 {
-	struct file_lock *fl, file_lock;
+	struct file_lock *fl, cfl, file_lock;
 	struct flock64 flock;
 	int error;
 
@@ -1741,7 +1746,7 @@ int fcntl_getlk64(struct file *filp, struct flock64 __user *l)
 		else
 		  fl = (file_lock.fl_type == F_UNLCK ? NULL : &file_lock);
 	} else {
-		fl = posix_test_lock(filp, &file_lock);
+		fl = (posix_test_lock(filp, &file_lock, &cfl) ? &cfl : NULL);
 	}
  
 	flock.l_type = F_UNLCK;

fs/nfs/file.c

@@ -392,15 +392,14 @@ nfs_file_write(struct kiocb *iocb, const char __user *buf, size_t count, loff_t
 
 static int do_getlk(struct file *filp, int cmd, struct file_lock *fl)
 {
-	struct file_lock *cfl;
+	struct file_lock cfl;
 	struct inode *inode = filp->f_mapping->host;
 	int status = 0;
 
 	lock_kernel();
 	/* Try local locking first */
-	cfl = posix_test_lock(filp, fl);
-	if (cfl != NULL) {
-		locks_copy_lock(fl, cfl);
+	if (posix_test_lock(filp, fl, &cfl)) {
+		locks_copy_lock(fl, &cfl);
 		goto out;
 	}
 

fs/nfsd/nfs4state.c

@@ -2639,7 +2639,7 @@ nfsd4_lock(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nfsd4_lock
 	struct nfs4_stateid *lock_stp;
 	struct file *filp;
 	struct file_lock file_lock;
-	struct file_lock *conflock;
+	struct file_lock conflock;
 	int status = 0;
 	unsigned int strhashval;
 
@@ -2775,11 +2775,11 @@ nfsd4_lock(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nfsd4_lock
 	/* XXX There is a race here. Future patch needed to provide 
 	 * an atomic posix_lock_and_test_file
 	 */
-	if (!(conflock = posix_test_lock(filp, &file_lock))) {
+	if (!posix_test_lock(filp, &file_lock, &conflock)) {
 		status = nfserr_serverfault;
 		goto out;
 	}
-	nfs4_set_lock_denied(conflock, &lock->lk_denied);
+	nfs4_set_lock_denied(&conflock, &lock->lk_denied);
 out:
 	if (status && lock->lk_is_new && lock_sop)
 		release_stateowner(lock_sop);
@@ -2800,7 +2800,7 @@ nfsd4_lockt(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nfsd4_lock
 	struct inode *inode;
 	struct file file;
 	struct file_lock file_lock;
-	struct file_lock *conflicting_lock;
+	struct file_lock conflock;
 	int status;
 
 	if (nfs4_in_grace())
@@ -2864,10 +2864,9 @@ nfsd4_lockt(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nfsd4_lock
 	file.f_dentry = current_fh->fh_dentry;
 
 	status = nfs_ok;
-	conflicting_lock = posix_test_lock(&file, &file_lock);
-	if (conflicting_lock) {
+	if (posix_test_lock(&file, &file_lock, &conflock)) {
 		status = nfserr_denied;
-		nfs4_set_lock_denied(conflicting_lock, &lockt->lt_denied);
+		nfs4_set_lock_denied(&conflock, &lockt->lt_denied);
 	}
 out:
 	nfs4_unlock_state();

include/linux/fs.h

@@ -754,7 +754,7 @@ extern void locks_init_lock(struct file_lock *);
 extern void locks_copy_lock(struct file_lock *, struct file_lock *);
 extern void locks_remove_posix(struct file *, fl_owner_t);
 extern void locks_remove_flock(struct file *);
-extern struct file_lock *posix_test_lock(struct file *, struct file_lock *);
+extern int posix_test_lock(struct file *, struct file_lock *, struct file_lock *);
 extern int posix_lock_file(struct file *, struct file_lock *);
 extern int posix_lock_file_wait(struct file *, struct file_lock *);
 extern int posix_unblock_lock(struct file *, struct file_lock *);