locks: fix locks_mandatory_locked to respect file-private locks

As Trond pointed out, you can currently deadlock yourself by setting a
file-private lock on a file that requires mandatory locking and then
trying to do I/O on it.

Avoid this problem by plumbing some knowledge of file-private locks into
the mandatory locking code. In order to do this, we must pass down
information about the struct file that's being used to
locks_verify_locked.
Reported-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Acked-by: J. Bruce Fields <bfields@redhat.com>

fs/locks.c

@@ -1155,13 +1155,14 @@ EXPORT_SYMBOL(posix_lock_file_wait);
 
 /**
  * locks_mandatory_locked - Check for an active lock
- * @inode: the file to check
+ * @file: the file to check
  *
  * Searches the inode's list of locks to find any POSIX locks which conflict.
  * This function is called from locks_verify_locked() only.
  */
-int locks_mandatory_locked(struct inode *inode)
+int locks_mandatory_locked(struct file *file)
 {
+	struct inode *inode = file_inode(file);
 	fl_owner_t owner = current->files;
 	struct file_lock *fl;
 
@@ -1172,7 +1173,7 @@ int locks_mandatory_locked(struct inode *inode)
 	for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
 		if (!IS_POSIX(fl))
 			continue;
-		if (fl->fl_owner != owner)
+		if (fl->fl_owner != owner && fl->fl_owner != (fl_owner_t)file)
 			break;
 	}
 	spin_unlock(&inode->i_lock);

fs/namei.c

@@ -2542,7 +2542,7 @@ static int handle_truncate(struct file *filp)
 	/*
 	 * Refuse to truncate files with mandatory locks held on them.
 	 */
-	error = locks_verify_locked(inode);
+	error = locks_verify_locked(filp);
 	if (!error)
 		error = security_path_truncate(path);
 	if (!error) {

include/linux/fs.h

@@ -1912,6 +1912,11 @@ extern int current_umask(void);
 extern void ihold(struct inode * inode);
 extern void iput(struct inode *);
 
+static inline struct inode *file_inode(struct file *f)
+{
+	return f->f_inode;
+}
+
 /* /sys/fs */
 extern struct kobject *fs_kobj;
 
@@ -1921,7 +1926,7 @@ extern struct kobject *fs_kobj;
 #define FLOCK_VERIFY_WRITE 2
 
 #ifdef CONFIG_FILE_LOCKING
-extern int locks_mandatory_locked(struct inode *);
+extern int locks_mandatory_locked(struct file *);
 extern int locks_mandatory_area(int, struct inode *, struct file *, loff_t, size_t);
 
 /*
@@ -1944,10 +1949,10 @@ static inline int mandatory_lock(struct inode *ino)
 	return IS_MANDLOCK(ino) && __mandatory_lock(ino);
 }
 
-static inline int locks_verify_locked(struct inode *inode)
+static inline int locks_verify_locked(struct file *file)
 {
-	if (mandatory_lock(inode))
-		return locks_mandatory_locked(inode);
+	if (mandatory_lock(file_inode(file)))
+		return locks_mandatory_locked(file);
 	return 0;
 }
 
@@ -2008,7 +2013,7 @@ static inline int break_deleg_wait(struct inode **delegated_inode)
 }
 
 #else /* !CONFIG_FILE_LOCKING */
-static inline int locks_mandatory_locked(struct inode *inode)
+static inline int locks_mandatory_locked(struct file *file)
 {
 	return 0;
 }
@@ -2030,7 +2035,7 @@ static inline int mandatory_lock(struct inode *inode)
 	return 0;
 }
 
-static inline int locks_verify_locked(struct inode *inode)
+static inline int locks_verify_locked(struct file *file)
 {
 	return 0;
 }
@@ -2297,11 +2302,6 @@ static inline bool execute_ok(struct inode *inode)
 	return (inode->i_mode & S_IXUGO) || S_ISDIR(inode->i_mode);
 }
 
-static inline struct inode *file_inode(struct file *f)
-{
-	return f->f_inode;
-}
-
 static inline void file_start_write(struct file *file)
 {
 	if (!S_ISREG(file_inode(file)->i_mode))

mm/mmap.c

@@ -1299,7 +1299,7 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
 			/*
 			 * Make sure there are no mandatory locks on the file.
 			 */
-			if (locks_verify_locked(inode))
+			if (locks_verify_locked(file))
 				return -EAGAIN;
 
 			vm_flags |= VM_SHARED | VM_MAYSHARE;

mm/nommu.c

@@ -995,7 +995,7 @@ static int validate_mmap_request(struct file *file,
 			    (file->f_mode & FMODE_WRITE))
 				return -EACCES;
 
-			if (locks_verify_locked(file_inode(file)))
+			if (locks_verify_locked(file))
 				return -EAGAIN;
 
 			if (!(capabilities & BDI_CAP_MAP_DIRECT))