2021-11-02 20:29:43

by Alexey Khoroshilov

Subject: [PATCH] sctp: avoid NULL pointer dereference in sctp_sf_violation

Some callers (e.g. sctp_sf_violation_chunk) passes NULL to
asoc argument of sctp_sf_violation. So, it should check it
before calling sctp_vtag_verify().

Probably it could be exploited by a malicious SCTP packet
to cause NULL pointer dereference.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Alexey Khoroshilov <[email protected]>
Fixes: aa0f697e4528 ("sctp: add vtag check in sctp_sf_violation")
---
net/sctp/sm_statefuns.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index fb3da4d8f4a3..77f3cd6c516e 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -4669,7 +4669,7 @@ enum sctp_disposition sctp_sf_violation(struct net *net,
{
struct sctp_chunk *chunk = arg;

- if (!sctp_vtag_verify(chunk, asoc))
+ if (asoc && !sctp_vtag_verify(chunk, asoc))
return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);

/* Make sure that the chunk has a valid length. */
--
2.7.4

2021-11-03 12:46:26

by Xin Long

Subject: Re: [PATCH] sctp: avoid NULL pointer dereference in sctp_sf_violation

On Tue, Nov 2, 2021 at 4:27 PM Alexey Khoroshilov <[email protected]> wrote:
>
> Some callers (e.g. sctp_sf_violation_chunk) passes NULL to
> asoc argument of sctp_sf_violation. So, it should check it
> before calling sctp_vtag_verify().
>
> Probably it could be exploited by a malicious SCTP packet
> to cause NULL pointer dereference.
I don't think asoc can be NULL in here, did you see any call trace
caused by it?

If this was found by a tool, please remove the unnecessary call from
sctp_sf_violation_chunk() instead:

@@ -4893,9 +4893,6 @@ static enum sctp_disposition sctp_sf_violation_chunk(
{
static const char err_str[] = "The following chunk violates protocol:";

- if (!asoc)
- return sctp_sf_violation(net, ep, asoc, type, arg, commands);
-

Thanks.

>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Signed-off-by: Alexey Khoroshilov <[email protected]>
> Fixes: aa0f697e4528 ("sctp: add vtag check in sctp_sf_violation")
> ---
> net/sctp/sm_statefuns.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
> index fb3da4d8f4a3..77f3cd6c516e 100644
> --- a/net/sctp/sm_statefuns.c
> +++ b/net/sctp/sm_statefuns.c
> @@ -4669,7 +4669,7 @@ enum sctp_disposition sctp_sf_violation(struct net *net,
> {
> struct sctp_chunk *chunk = arg;
>
> - if (!sctp_vtag_verify(chunk, asoc))
> + if (asoc && !sctp_vtag_verify(chunk, asoc))
> return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
>
> /* Make sure that the chunk has a valid length. */
> --
> 2.7.4
>

2021-11-05 19:28:25

by Alexey Khoroshilov

Subject: [PATCH] sctp: remove unreachable code from sctp_sf_violation_chunk()

sctp_sf_violation_chunk() is not called with asoc argument equal to NULL,
but if that happens it would lead to NULL pointer dereference
in sctp_vtag_verify().

The patch removes code that handles NULL asoc in sctp_sf_violation_chunk().

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Alexey Khoroshilov <[email protected]>
Proposed-by: Xin Long <[email protected]>
---
net/sctp/sm_statefuns.c | 3 ---
1 file changed, 3 deletions(-)

diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index fb3da4d8f4a3..ec8561dd7e76 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -4893,9 +4893,6 @@ static enum sctp_disposition sctp_sf_violation_chunk(
{
static const char err_str[] = "The following chunk violates protocol:";

- if (!asoc)
- return sctp_sf_violation(net, ep, asoc, type, arg, commands);
-
return sctp_sf_abort_violation(net, ep, asoc, arg, commands, err_str,
sizeof(err_str));
}
--
2.7.4

2021-11-08 00:50:58

by patchwork-bot+netdevbpf

Subject: Re: [PATCH] sctp: remove unreachable code from sctp_sf_violation_chunk()

Hello:

This patch was applied to netdev/net.git (master)
by David S. Miller <[email protected]>:

On Fri, 5 Nov 2021 20:30:27 +0300 you wrote:
> sctp_sf_violation_chunk() is not called with asoc argument equal to NULL,
> but if that happens it would lead to NULL pointer dereference
> in sctp_vtag_verify().
>
> The patch removes code that handles NULL asoc in sctp_sf_violation_chunk().
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> [...]

Here is the summary with links:
- sctp: remove unreachable code from sctp_sf_violation_chunk()
https://git.kernel.org/netdev/net/c/e7ea51cd879c

You are awesome, thank you!
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