bpf: Allow delete from sockmap/sockhash only if update is allowed

We have seen an influx of syzkaller reports where a BPF program attached to
a tracepoint triggers a locking rule violation by performing a map_delete
on a sockmap/sockhash.

We don't intend to support this artificial use scenario. Extend the
existing verifier allowed-program-type check for updating sockmap/sockhash
to also cover deleting from a map.

From now on only BPF programs which were previously allowed to update
sockmap/sockhash can delete from these map types.

Fixes: ff9105993240 ("bpf, sockmap: Prevent lock inversion deadlock in map delete elem")
Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Reported-by: syzbot+ec941d6e24f633a59172@syzkaller.appspotmail.com
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: syzbot+ec941d6e24f633a59172@syzkaller.appspotmail.com
Acked-by: John Fastabend <john.fastabend@gmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=ec941d6e24f633a59172
Link: https://lore.kernel.org/bpf/20240527-sockmap-verify-deletes-v1-1-944b372f2101@cloudflare.com

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 77da1f438beccec71f59a4b129323a1064389e12..48f3a9acdef3d4f206c8fef1067195404e9438be 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8882,7 +8882,8 @@ static bool may_update_sockmap(struct bpf_verifier_env *env, int func_id)
        enum bpf_attach_type eatype = env->prog->expected_attach_type;
        enum bpf_prog_type type = resolve_prog_type(env->prog);
 
-       if (func_id != BPF_FUNC_map_update_elem)
+       if (func_id != BPF_FUNC_map_update_elem &&
+           func_id != BPF_FUNC_map_delete_elem)
                return false;
 
        /* It's not possible to get access to a locked struct sock in these
@@ -8893,6 +8894,11 @@ static bool may_update_sockmap(struct bpf_verifier_env *env, int func_id)
                if (eatype == BPF_TRACE_ITER)
                        return true;
                break;
+       case BPF_PROG_TYPE_SOCK_OPS:
+               /* map_update allowed only via dedicated helpers with event type checks */
+               if (func_id == BPF_FUNC_map_delete_elem)
+                       return true;
+               break;
        case BPF_PROG_TYPE_SOCKET_FILTER:
        case BPF_PROG_TYPE_SCHED_CLS:
        case BPF_PROG_TYPE_SCHED_ACT:
@@ -8988,7 +8994,6 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
        case BPF_MAP_TYPE_SOCKMAP:
                if (func_id != BPF_FUNC_sk_redirect_map &&
                    func_id != BPF_FUNC_sock_map_update &&
-                   func_id != BPF_FUNC_map_delete_elem &&
                    func_id != BPF_FUNC_msg_redirect_map &&
                    func_id != BPF_FUNC_sk_select_reuseport &&
                    func_id != BPF_FUNC_map_lookup_elem &&
@@ -8998,7 +9003,6 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
        case BPF_MAP_TYPE_SOCKHASH:
                if (func_id != BPF_FUNC_sk_redirect_hash &&
                    func_id != BPF_FUNC_sock_hash_update &&
-                   func_id != BPF_FUNC_map_delete_elem &&
                    func_id != BPF_FUNC_msg_redirect_hash &&
                    func_id != BPF_FUNC_sk_select_reuseport &&
                    func_id != BPF_FUNC_map_lookup_elem &&