[PATCH 6.1 452/473] bpf: Allow delete from sockmap/sockhash only if update is allowed

Greg Kroah-Hartman
2024-06-06T14:20:30Z

From: Jakub Sitnicki <jakub@cloudflare.com>

[ Upstream commit 98e948fb60d41447fd8d2d0c3b8637fc6b6dc26d ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/bpf/verifier.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 18b3f429abe17..1d851e2f48590 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6492,7 +6492,8 @@ 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
@@ -6503,6 +6504,11 @@ 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:
@@ -6598,7 +6604,6 @@ 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 &&
@@ -6608,7 +6613,6 @@ 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 &&
--
2.43.0