Re: [PATCH bpf-next] bpf: Make sure internal and UAPI bpf_redirect flags don't overlap

[Daniel Borkmann <daniel@xxxxxxxxxxxxx>]

On 9/20/24 2:56 PM, Toke Høiland-Jørgensen wrote:
> The bpf_redirect_info is shared between the SKB and XDP redirect paths,
> and the two paths use the same numeric flag values in the ri->flags
> field (specifically, BPF_F_BROADCAST == BPF_F_NEXTHOP). This means that
> if skb bpf_redirect_neigh() is used with a non-NULL params argument and,
> subsequently, an XDP redirect is performed using the same
> bpf_redirect_info struct, the XDP path will get confused and end up
> crashing, which syzbot managed to trigger.
>
> With the stack-allocated bpf_redirect_info, the structure is no longer
> shared between the SKB and XDP paths, so the crash doesn't happen
> anymore. However, different code paths using identically-numbered flag
> values in the same struct field still seems like a bit of a mess, so
> this patch cleans that up by moving the flag definitions together and
> redefining the three flags in BPF_F_REDIRECT_INTERNAL to not overlap
> with the flags used for XDP. It also adds a BUILD_BUG_ON() check to make
> sure the overlap is not re-introduced by mistake.
>
> Fixes: e624d4ed4aa8 ("xdp: Extend xdp_redirect_map with broadcast support")
> Reported-by: syzbot+cca39e6e84a367a7e6f6@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=cca39e6e84a367a7e6f6
> Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
> ---
>   include/uapi/linux/bpf.h | 14 ++++++--------
>   net/core/filter.c        |  8 +++++---
>   2 files changed, 11 insertions(+), 11 deletions(-)
Lgtm, applied, thanks! I also added a tools header sync.I took this into 
bpf tree, so that stable can pick it up.
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index c3a5728db115..0c6154272ab3 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -6047,11 +6047,6 @@ enum {
>   	BPF_F_MARK_ENFORCE		= (1ULL << 6),
>   };
>   
> -/* BPF_FUNC_clone_redirect and BPF_FUNC_redirect flags. */
> -enum {
> -	BPF_F_INGRESS			= (1ULL << 0),
> -};
> -
>   /* BPF_FUNC_skb_set_tunnel_key and BPF_FUNC_skb_get_tunnel_key flags. */
>   enum {
>   	BPF_F_TUNINFO_IPV6		= (1ULL << 0),
> @@ -6198,11 +6193,14 @@ enum {
>   	BPF_F_BPRM_SECUREEXEC	= (1ULL << 0),
>   };
>   
> -/* Flags for bpf_redirect_map helper */
> +/* Flags for bpf_redirect and bpf_redirect_map helpers */
>   enum {
> -	BPF_F_BROADCAST		= (1ULL << 3),
> -	BPF_F_EXCLUDE_INGRESS	= (1ULL << 4),
> +	BPF_F_INGRESS		= (1ULL << 0), /* used for skb path */
> +	BPF_F_BROADCAST		= (1ULL << 3), /* used for XDP path */
> +	BPF_F_EXCLUDE_INGRESS	= (1ULL << 4), /* used for XDP path */
>   };
> +#define BPF_F_REDIRECT_ALL_FLAGS (BPF_F_INGRESS | BPF_F_BROADCAST | BPF_F_EXCLUDE_INGRESS)
> +
>   
Also fixed up extra newline.

Thanks,
Daniel