From d8e9e5e80e882b4f90cba7edf1e6cb7376e52e54 Mon Sep 17 00:00:00 2001 From: Richard Weinberger Date: Wed, 9 Nov 2016 22:52:58 +0100 Subject: [PATCH] drbd: Fix kernel_sendmsg() usage - potential NULL deref Don't pass a size larger than iov_len to kernel_sendmsg(). Otherwise it will cause a NULL pointer deref when kernel_sendmsg() returns with rv < size. DRBD as external module has been around in the kernel 2.4 days already. We used to be compatible to 2.4 and very early 2.6 kernels, we used to use rv = sock_sendmsg(sock, &msg, iov.iov_len); then later changed to rv = kernel_sendmsg(sock, &msg, &iov, 1, size); when we should have used rv = kernel_sendmsg(sock, &msg, &iov, 1, iov.iov_len); tcp_sendmsg() used to totally ignore the size parameter. 57be5bd ip: convert tcp_sendmsg() to iov_iter primitives changes that, and exposes our long standing error. Even with this error exposed, to trigger the bug, we would need to have an environment (config or otherwise) causing us to not use sendpage() for larger transfers, a failing connection, and have it fail "just at the right time". Apparently that was unlikely enough for most, so this went unnoticed for years. Still, it is known to trigger at least some of these, and suspected for the others: [0] http://lists.linbit.com/pipermail/drbd-user/2016-July/023112.html [1] http://lists.linbit.com/pipermail/drbd-dev/2016-March/003362.html [2] https://forums.grsecurity.net/viewtopic.php?f=3&t=4546 [3] https://ubuntuforums.org/showthread.php?t=2336150 [4] http://e2.howsolveproblem.com/i/1175162/ This should go into 4.9, and into all stable branches since and including v4.0, which is the first to contain the exposing change. It is correct for all stable branches older than that as well (which contain the DRBD driver; which is 2.6.33 and up). It requires a small "conflict" resolution for v4.4 and earlier, with v4.5 we dropped the comment block immediately preceding the kernel_sendmsg(). Fixes: b411b3637fa7 ("The DRBD driver") Cc: # 2.6.33.x- Cc: viro@zeniv.linux.org.uk Cc: christoph.lechleitner@iteg.at Cc: wolfgang.glas@iteg.at Reported-by: Christoph Lechleitner Tested-by: Christoph Lechleitner Signed-off-by: Richard Weinberger [changed oneliner to be "obvious" without context; more verbose message] Signed-off-by: Lars Ellenberg Signed-off-by: Jens Axboe --- drivers/block/drbd/drbd_main.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c index 100be556e613..83482721bc01 100644 --- a/drivers/block/drbd/drbd_main.c +++ b/drivers/block/drbd/drbd_main.c @@ -1871,7 +1871,7 @@ int drbd_send(struct drbd_connection *connection, struct socket *sock, drbd_update_congested(connection); } do { - rv = kernel_sendmsg(sock, &msg, &iov, 1, size); + rv = kernel_sendmsg(sock, &msg, &iov, 1, iov.iov_len); if (rv == -EAGAIN) { if (we_should_drop_the_connection(connection, sock)) break; -- 2.20.1