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

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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




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