Re: [PATCH bpf] bpf: Fix NULL pointer dereference in bpf_sock_from_file

["Emil Tsalapatis" <emil@etsalapatis.com>]

On Tue Aug 18, 2026 at 1:42 PM EDT, MahnurA wrote:
> bpf_sock_from_file should not dereference a NULL file pointer.
> KASAN detects a null-ptr-deref when eBPF tracing
> fentry/fexit programs are attached to points such as
> __mmap_region and file_map_prot_check kernel functions. This can
> result in a NULL file pointer flowing from context to the helper.
>
> A minimal check before dereferencing can fix this.
>
> Fixes: b60da4955f53 ("bpf: Only provide bpf_sock_from_file with CONFIG_NET")
> Signed-off-by: MahnurA <s.mahnur.a@gmail.com>

Patch looks fine and the crash replicates. Please resend with a full
name since we don't take pseudonymous contributions. Once you do,
please feel free to add my reviewed-by tag.

pw-bot: cr

> ---
>  net/core/filter.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 16845987b244..7c3caae4bafc 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -12182,7 +12182,10 @@ const struct bpf_func_proto bpf_skc_to_mptcp_sock_proto = {
>  
>  BPF_CALL_1(bpf_sock_from_file, struct file *, file)
>  {
> -	return (unsigned long)sock_from_file(file);
> +	if (file)
> +		return (unsigned long)sock_from_file(file);
> +
> +	return (unsigned long)NULL;
>  }
>  
>  BTF_ID_LIST(bpf_sock_from_file_btf_ids)