Re: [PATCH] selftests/bpf: Fix null pointer check in skb_pkt_end.c

[Martin KaFai Lau]

On 4/22/25 11:23 AM, Prabhav Kumar Vaish wrote:
Ensure that 'tcp' is checked for NULL before dereferencing. This resolves
a potential null pointer dereference warning reported by static analysis.
Signed-off-by: Prabhav Kumar Vaish <pvkumar5749...@gmail.com>
---
  tools/testing/selftests/bpf/progs/skb_pkt_end.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/skb_pkt_end.c 
b/tools/testing/selftests/bpf/progs/skb_pkt_end.c
index 3bb4451524a1..db33ff2839f7 100644
--- a/tools/testing/selftests/bpf/progs/skb_pkt_end.c
+++ b/tools/testing/selftests/bpf/progs/skb_pkt_end.c
@@ -45,10 +45,10 @@ int main_prog(struct __sk_buff *skb)
                goto out;
  
  	tcp = (void*)(ip + 1);
-       if (tcp->dest != 0)
-               goto out;
        if (!tcp)

This case will never be hit, so this change is not doing anything other than 
silencing the static checker. Take a look at commit 9cc873e85800 
("selftests/bpf: Add skb_pkt_end test"). The test was written to have a specific 
llvm generated code. You will need to check the generated code is still testing 
what it is supposed to test.

pw-bot: cr

                goto out;
+       if (tcp->dest != 0)
+               goto out;
  
  	urg_ptr = tcp->urg_ptr;