[PATCH 3.16.y-ckt 132/142] AIO: properly check iovec sizes

[Luis Henriques]

3.16.7-ckt26 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Greg Kroah-Hartman <gregkh at linuxfoundation.org>

In Linus's tree, the iovec code has been reworked massively, but in
older kernels the AIO layer should be checking this before passing the
request on to other layers.

Many thanks to Ben Hawkes of Google Project Zero for pointing out the
issue.

Reported-by: Ben Hawkes <hawkes at google.com>
Acked-by: Benjamin LaHaise <bcrl at kvack.org>
Tested-by: Willy Tarreau <w at 1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: Moritz Muehlenhoff <jmm at inutil.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/aio.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index a6f86dae34be..7aaa4164bba5 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1378,11 +1378,16 @@ static ssize_t aio_setup_single_vector(struct kiocb *kiocb,
 				       unsigned long *nr_segs,
 				       struct iovec *iovec)
 {
-	if (unlikely(!access_ok(!rw, buf, kiocb->ki_nbytes)))
+	size_t len = kiocb->ki_nbytes;
+
+	if (len > MAX_RW_COUNT)
+		len = MAX_RW_COUNT;
+
+	if (unlikely(!access_ok(!rw, buf, len)))
 		return -EFAULT;
 
 	iovec->iov_base = buf;
-	iovec->iov_len = kiocb->ki_nbytes;
+	iovec->iov_len = len;
 	*nr_segs = 1;
 	return 0;
 }