From: Richard Weinberger <richard@xxxxxx> 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: <stable@xxxxxxxxxxxxxxx> # 2.6.33.x- Cc: viro@xxxxxxxxxxxxxxxxxx Cc: christoph.lechleitner@xxxxxxx Cc: wolfgang.glas@xxxxxxx Reported-by: Christoph Lechleitner <christoph.lechleitner@xxxxxxx> Tested-by: Christoph Lechleitner <christoph.lechleitner@xxxxxxx> Signed-off-by: Richard Weinberger <richard@xxxxxx> [changed oneliner to be "obvious" without context; more verbose message] Signed-off-by: Lars Ellenberg <lars.ellenberg@xxxxxxxxxx> --- 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 100be55..8348272 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; -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html