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bpf: Make sure internal and UAPI bpf_redirect flags don't overlap

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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: e624d4ed4a ("xdp: Extend xdp_redirect_map with broadcast support")
Reported-by: syzbot+cca39e6e84a367a7e6f6@syzkaller.appspotmail.com
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Closes: https://syzkaller.appspot.com/bug?extid=cca39e6e84a367a7e6f6
Link: https://lore.kernel.org/bpf/20240920125625.59465-1-toke@redhat.com
This commit is contained in:
Toke Høiland-Jørgensen
2024-09-20 14:56:24 +02:00
committed by Daniel Borkmann
parent a41b3828ec
commit 09d88791c7
2 changed files with 10 additions and 11 deletions
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include/uapi/linux/bpf.h
+5 -8
View File
@@ -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),
@@ -6198,10 +6193,12 @@ 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_FLAGS (BPF_F_INGRESS | BPF_F_BROADCAST | BPF_F_EXCLUDE_INGRESS)
};
#define __bpf_md_ptr(type, name) \