cipso: harden use of skb_cow() in cipso_v4_skbuff_setattr()

If skb_cow() is passed a headroom <= -NET_SKB_PAD, it will trigger a
BUG. As a result, use cases should avoid calling with a headroom that
is negative to prevent triggering this issue.

This is the same code pattern fixed in Commit 58fc7342b529 ("ipv6:
BUG() in pskb_expand_head() as part of calipso_skbuff_setattr()").

In cipso_v4_skbuff_setattr(), len_delta can become negative, leading to
a negative headroom passed to skb_cow(). However, the BUG is not
triggerable because the condition headroom <= -NET_SKB_PAD cannot be
satisfied due to limits on the IPv4 options header size.

Avoid potential problems in the future by only using skb_cow() to grow
the skb headroom.

Signed-off-by: Will Rosenberg <whrosenb@asu.edu>
Acked-by: Paul Moore <paul@paul-moore.com>
Link: https://patch.msgid.link/20260120155738.982771-1-whrosenb@asu.edu
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
index 709021197e1caac4a0a56325fac46d36ab46499d..32b951ebc0c2b953a03566af91c3da349d0d9c70 100644 (file)
--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c
@@ -2196,7 +2196,8 @@ int cipso_v4_skbuff_setattr(struct sk_buff *skb,
        /* if we don't ensure enough headroom we could panic on the skb_push()
         * call below so make sure we have enough, we are also "mangling" the
         * packet so we should probably do a copy-on-write call anyway */
-       ret_val = skb_cow(skb, skb_headroom(skb) + len_delta);
+       ret_val = skb_cow(skb,
+                         skb_headroom(skb) + (len_delta > 0 ? len_delta : 0));
        if (ret_val < 0)
                return ret_val;