linux-kernel - [ 015/153] ext4: fix possible use-after-free with AIO

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Message-Id: <20130304033709.092475518@decadent.org.uk>
Date:	Mon, 04 Mar 2013 03:37:22 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, Jan Kara <jack@...e.cz>,
	Carlos Maiolino <cmaiolino@...hat.com>,
	Jeff Moyer <jmoyer@...hat.com>, "Theodore Tso" <tytso@....edu>
Subject: [ 015/153] ext4: fix possible use-after-free with AIO

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@...e.cz>

commit 091e26dfc156aeb3b73bc5c5f277e433ad39331c upstream.

Running AIO is pinning inode in memory using file reference. Once AIO
is completed using aio_complete(), file reference is put and inode can
be freed from memory. So we have to be sure that calling aio_complete()
is the last thing we do with the inode.

Reviewed-by: Carlos Maiolino <cmaiolino@...hat.com>
Acked-by: Jeff Moyer <jmoyer@...hat.com>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ext4/inode.c   |    2 +-
 fs/ext4/page-io.c |    9 ++++-----
 2 files changed, 5 insertions(+), 6 deletions(-)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2795,9 +2795,9 @@ static void ext4_end_io_dio(struct kiocb
 	if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
 		ext4_free_io_end(io_end);
 out:
+		inode_dio_done(inode);
 		if (is_async)
 			aio_complete(iocb, ret, 0);
-		inode_dio_done(inode);
 		return;
 	}
 
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -108,14 +108,13 @@ int ext4_end_io_nolock(ext4_io_end_t *io
 			 inode->i_ino, offset, size, ret);
 	}
 
-	if (io->iocb)
-		aio_complete(io->iocb, io->result, 0);
-
-	if (io->flag & EXT4_IO_END_DIRECT)
-		inode_dio_done(inode);
 	/* Wake up anyone waiting on unwritten extent conversion */
 	if (atomic_dec_and_test(&EXT4_I(inode)->i_aiodio_unwritten))
 		wake_up_all(ext4_ioend_wq(io->inode));
+	if (io->flag & EXT4_IO_END_DIRECT)
+		inode_dio_done(inode);
+	if (io->iocb)
+		aio_complete(io->iocb, io->result, 0);
 	return ret;
 }
 


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