[PATCH net] ipv6: Fix return value of ipv6_mc_may_pull() for malformed packets

Commit ba5ea614622d ("bridge: simplify ip_mc_check_igmp() and
ipv6_mc_check_mld() calls") replaces direct calls to pskb_may_pull()
in br_ipv6_multicast_mld2_report() with calls to ipv6_mc_may_pull(),
that returns -EINVAL on buffers too short to be valid IPv6 packets,
while maintaining the previous handling of the return code.

This leads to the direct opposite of the intended effect: if the
packet is malformed, -EINVAL evaluates as true, and we'll happily
proceed with the processing.

Return 0 if the packet is too short, in the same way as this was
fixed for IPv4 by commit 083b78a9ed64 ("ip: fix ip_mc_may_pull()
return value").

I don't have a reproducer for this, unlike the one referred to by
the IPv4 commit, but this is clearly broken.

Fixes: ba5ea614622d ("bridge: simplify ip_mc_check_igmp() and ipv6_mc_check_mld() calls")
Signed-off-by: Stefano Brivio <redacted>
---
 include/net/addrconf.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/addrconf.h b/include/net/addrconf.h
index becdad576859..3f62b347b04a 100644
--- a/include/net/addrconf.h
+++ b/include/net/addrconf.h

@@ -206,7 +206,7 @@ static inline int ipv6_mc_may_pull(struct sk_buff *skb,
 				   unsigned int len)
 {
 	if (skb_transport_offset(skb) + ipv6_transport_len(skb) < len)
-		return -EINVAL;
+		return 0;
 
 	return pskb_may_pull(skb, len);
 }

-- 
2.20.1

On Tue, Aug 13, 2019 at 12:46:01AM +0200, Stefano Brivio wrote:

Acked-by: Guillaume Nault <redacted>

From: Stefano Brivio <redacted>
Date: Tue, 13 Aug 2019 00:46:01 +0200

Commit ba5ea614622d ("bridge: simplify ip_mc_check_igmp() and
ipv6_mc_check_mld() calls") replaces direct calls to pskb_may_pull()
in br_ipv6_multicast_mld2_report() with calls to ipv6_mc_may_pull(),
that returns -EINVAL on buffers too short to be valid IPv6 packets,
while maintaining the previous handling of the return code.

This leads to the direct opposite of the intended effect: if the
packet is malformed, -EINVAL evaluates as true, and we'll happily
proceed with the processing.

Return 0 if the packet is too short, in the same way as this was
fixed for IPv4 by commit 083b78a9ed64 ("ip: fix ip_mc_may_pull()
return value").

I don't have a reproducer for this, unlike the one referred to by
the IPv4 commit, but this is clearly broken.

Fixes: ba5ea614622d ("bridge: simplify ip_mc_check_igmp() and ipv6_mc_check_mld() calls")
Signed-off-by: Stefano Brivio <redacted>

Applied and queued up for -stable.

On Wed, Aug 14, 2019 at 12:58:58PM -0400, David Miller wrote:

From: Stefano Brivio <redacted>
Date: Tue, 13 Aug 2019 00:46:01 +0200

quoted

Commit ba5ea614622d ("bridge: simplify ip_mc_check_igmp() and
ipv6_mc_check_mld() calls") replaces direct calls to pskb_may_pull()
in br_ipv6_multicast_mld2_report() with calls to ipv6_mc_may_pull(),
that returns -EINVAL on buffers too short to be valid IPv6 packets,
while maintaining the previous handling of the return code.

This leads to the direct opposite of the intended effect: if the
packet is malformed, -EINVAL evaluates as true, and we'll happily
proceed with the processing.

Return 0 if the packet is too short, in the same way as this was
fixed for IPv4 by commit 083b78a9ed64 ("ip: fix ip_mc_may_pull()
return value").

I don't have a reproducer for this, unlike the one referred to by
the IPv4 commit, but this is clearly broken.

Fixes: ba5ea614622d ("bridge: simplify ip_mc_check_igmp() and ipv6_mc_check_mld() calls")
Signed-off-by: Stefano Brivio <redacted>

Applied and queued up for -stable.

Urgh, sorry... and thanks for the fix(es), absolutely right...

Hi,

On Wed, 14 Aug 2019 12:58:58 -0400 (EDT)
David Miller [off-list ref] wrote:

From: Stefano Brivio <redacted>
Date: Tue, 13 Aug 2019 00:46:01 +0200

quoted

Commit ba5ea614622d ("bridge: simplify ip_mc_check_igmp() and
ipv6_mc_check_mld() calls") replaces direct calls to pskb_may_pull()
in br_ipv6_multicast_mld2_report() with calls to ipv6_mc_may_pull(),
that returns -EINVAL on buffers too short to be valid IPv6 packets,
while maintaining the previous handling of the return code.

This leads to the direct opposite of the intended effect: if the
packet is malformed, -EINVAL evaluates as true, and we'll happily
proceed with the processing.

Return 0 if the packet is too short, in the same way as this was
fixed for IPv4 by commit 083b78a9ed64 ("ip: fix ip_mc_may_pull()
return value").

I don't have a reproducer for this, unlike the one referred to by
the IPv4 commit, but this is clearly broken.

Fixes: ba5ea614622d ("bridge: simplify ip_mc_check_igmp() and ipv6_mc_check_mld() calls")
Signed-off-by: Stefano Brivio <redacted>  

Applied and queued up for -stable.

I don't see this on net.git, but it's in your stable bundle on
Patchwork. Should I resend? Thanks.

-- 
Stefano

From: Stefano Brivio <redacted>
Date: Mon, 19 Aug 2019 12:12:52 +0200

I don't see this on net.git, but it's in your stable bundle on
Patchwork. Should I resend? Thanks.

I applied it on my laptop while travelling and never pushed it out so it
just rot there, sorry.

Fixed, should be in 'net' now.