[PATCH 3.8 32/81] net: sctp: fix smatch warning in sctp_send_asconf_del_ip

From: Kamal Mostafa
Date: Tue Oct 29 2013 - 14:19:19 EST -stable review patch. If anyone has any objections, please let me know.


From: Daniel Borkmann <dborkman@xxxxxxxxxx>

[ Upstream commit 88362ad8f9a6cea787420b57cc27ccacef000dbe ]

This was originally reported in [1] and posted by Neil Horman [2], he said:

Fix up a missed null pointer check in the asconf code. If we don't find
a local address, but we pass in an address length of more than 1, we may
dereference a NULL laddr pointer. Currently this can't happen, as the only
users of the function pass in the value 1 as the addrcnt parameter, but
its not hot path, and it doesn't hurt to check for NULL should that ever
be the case.

The callpath from sctp_asconf_mgmt() looks okay. But this could be triggered
from sctp_setsockopt_bindx() call with SCTP_BINDX_REM_ADDR and addrcnt > 1
while passing all possible addresses from the bind list to SCTP_BINDX_REM_ADDR
so that we do *not* find a single address in the association's bind address
list that is not in the packed array of addresses. If this happens when we
have an established association with ASCONF-capable peers, then we could get
a NULL pointer dereference as we only check for laddr == NULL && addrcnt == 1
and call later sctp_make_asconf_update_ip() with NULL laddr.

BUT: this actually won't happen as sctp_bindx_rem() will catch such a case
and return with an error earlier. As this is incredably unintuitive and error
prone, add a check to catch at least future bugs here. As Neil says, its not
hot path. Introduced by 8a07eb0a5 ("sctp: Add ASCONF operation on the
single-homed host").

[1] http://www.spinics.net/lists/linux-sctp/msg02132.html
[2] http://www.spinics.net/lists/linux-sctp/msg02133.html

Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
Signed-off-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
Cc: Michio Honda <micchie@xxxxxxxxxxxxxx>
Acked-By: Neil Horman <nhorman@xxxxxxxxxxxxx>
Acked-by: Vlad Yasevich <vyasevich@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
net/sctp/socket.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index ea5c61a..89714ee 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -820,6 +820,9 @@ static int sctp_send_asconf_del_ip(struct sock *sk,
goto skip_mkasconf;

+ if (laddr == NULL)
+ return -EINVAL;
/* We do not need RCU protection throughout this loop
* because this is done under a socket lock from the
* setsockopt call.

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