Commit f523deed authored by Richard Weinberger's avatar Richard Weinberger Committed by Greg Kroah-Hartman

drbd: Fix kernel_sendmsg() usage - potential NULL deref

commit d8e9e5e8 upstream.

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.
 57be5bda 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: b411b363 ("The DRBD driver")
Cc: viro@zeniv.linux.org.uk
Cc: christoph.lechleitner@iteg.at
Cc: wolfgang.glas@iteg.at
Reported-by: default avatarChristoph Lechleitner <christoph.lechleitner@iteg.at>
Tested-by: default avatarChristoph Lechleitner <christoph.lechleitner@iteg.at>
Signed-off-by: default avatarRichard Weinberger <richard@nod.at>
[changed oneliner to be "obvious" without context; more verbose message]
Signed-off-by: default avatarLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent f1de3223
......@@ -1802,7 +1802,7 @@ int drbd_send(struct drbd_connection *connection, struct socket *sock,
* do we need to block DRBD_SIG if sock == &meta.socket ??
* otherwise wake_asender() might interrupt some send_*Ack !
*/
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;
......
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