[patch for 2.6.29? 1/3] pipe_rdwr_fasync: fix the error handling to prevent the leak/crash

[akpm@linux-foundation.org]

From: Oleg Nesterov <oleg@redhat.com>

If the second fasync_helper() fails, pipe_rdwr_fasync() returns the error
but leaves the file on ->fasync_readers.

This was always wrong, but since 233e70f4228e78eb2f80dc6650f65d3ae3dbf17c
"saner FASYNC handling on file close" we have the new problem.  Because in
this case setfl() doesn't set FASYNC bit, __fput() will not do
->fasync(0), and we leak fasync_struct with ->fa_file pointing to the
freed file.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: <stable@kernel.org>		[2.6.28.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/pipe.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff -puN fs/pipe.c~pipe_rdwr_fasync-fix-the-error-handling-to-prevent-the-leak-crash fs/pipe.c
--- a/fs/pipe.c~pipe_rdwr_fasync-fix-the-error-handling-to-prevent-the-leak-crash
+++ a/fs/pipe.c
@@ -693,11 +693,12 @@ pipe_rdwr_fasync(int fd, struct file *fi
 	int retval;
 
 	mutex_lock(&inode->i_mutex);
-
 	retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);
-	if (retval >= 0)
+	if (retval >= 0) {
 		retval = fasync_helper(fd, filp, on, &pipe->fasync_writers);
-
+		if (retval < 0) /* this can happen only if on == T */
+			fasync_helper(-1, filp, 0, &pipe->fasync_readers);
+	}
 	mutex_unlock(&inode->i_mutex);
 	return retval;
 }
_