From: John Fastabend john.fastabend@gmail.com
[ Upstream commit 218d747a4142f281a256687bb513a135c905867b ]
sock_map_link() is called to update a sockmap entry with a sk. But, if the sock_map_init_proto() call fails then we return an error to the map_update op against the sockmap. In the error path though we need to cleanup psock and dec the refcnt on any programs associated with the map, because we refcnt them early in the update process to ensure they are pinned for the psock. (This avoids a race where user deletes programs while also updating the map with new socks.)
In current code we do the prog refcnt dec explicitely by calling bpf_prog_put() when the program was found in the map. But, after commit '38207a5e81230' in this error path we've already done the prog to psock assignment so the programs have a reference from the psock as well. This then causes the psock tear down logic, invoked by sk_psock_put() in the error path, to similarly call bpf_prog_put on the programs there.
To be explicit this logic does the prog->psock assignment:
if (msg_*) psock_set_prog(...)
Then the error path under the out_progs label does a similar check and dec with:
if (msg_*) bpf_prog_put(...)
And the teardown logic sk_psock_put() does ...
psock_set_prog(msg_*, NULL)
... triggering another bpf_prog_put(...). Then KASAN gives us this splat, found by syzbot because we've created an inbalance between bpf_prog_inc and bpf_prog_put calling put twice on the program.
BUG: KASAN: vmalloc-out-of-bounds in __bpf_prog_put kernel/bpf/syscall.c:1812 [inline] BUG: KASAN: vmalloc-out-of-bounds in __bpf_prog_put kernel/bpf/syscall.c:1812 [inline] kernel/bpf/syscall.c:1829 BUG: KASAN: vmalloc-out-of-bounds in bpf_prog_put+0x8c/0x4f0 kernel/bpf/syscall.c:1829 kernel/bpf/syscall.c:1829 Read of size 8 at addr ffffc90000e76038 by task syz-executor020/3641
To fix clean up error path so it doesn't try to do the bpf_prog_put in the error path once progs are assigned then it relies on the normal psock tear down logic to do complete cleanup.
For completness we also cover the case whereh sk_psock_init_strp() fails, but this is not expected because it indicates an incorrect socket type and should be caught earlier.
Fixes: 38207a5e8123 ("bpf, sockmap: Attach map progs to psock early for feature probes") Reported-by: syzbot+bb73e71cf4b8fd376a4f@syzkaller.appspotmail.com Signed-off-by: John Fastabend john.fastabend@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Link: https://lore.kernel.org/bpf/20220104214645.290900-1-john.fastabend@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/core/sock_map.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-)
diff --git a/net/core/sock_map.c b/net/core/sock_map.c index 4ca4b11f4e5ff..687c81386518c 100644 --- a/net/core/sock_map.c +++ b/net/core/sock_map.c @@ -292,15 +292,23 @@ static int sock_map_link(struct bpf_map *map, struct sock *sk) if (skb_verdict) psock_set_prog(&psock->progs.skb_verdict, skb_verdict);
+ /* msg_* and stream_* programs references tracked in psock after this + * point. Reference dec and cleanup will occur through psock destructor + */ ret = sock_map_init_proto(sk, psock); - if (ret < 0) - goto out_drop; + if (ret < 0) { + sk_psock_put(sk, psock); + goto out; + }
write_lock_bh(&sk->sk_callback_lock); if (stream_parser && stream_verdict && !psock->saved_data_ready) { ret = sk_psock_init_strp(sk, psock); - if (ret) - goto out_unlock_drop; + if (ret) { + write_unlock_bh(&sk->sk_callback_lock); + sk_psock_put(sk, psock); + goto out; + } sk_psock_start_strp(sk, psock); } else if (!stream_parser && stream_verdict && !psock->saved_data_ready) { sk_psock_start_verdict(sk,psock); @@ -309,10 +317,6 @@ static int sock_map_link(struct bpf_map *map, struct sock *sk) } write_unlock_bh(&sk->sk_callback_lock); return 0; -out_unlock_drop: - write_unlock_bh(&sk->sk_callback_lock); -out_drop: - sk_psock_put(sk, psock); out_progs: if (skb_verdict) bpf_prog_put(skb_verdict); @@ -325,6 +329,7 @@ out_put_stream_parser: out_put_stream_verdict: if (stream_verdict) bpf_prog_put(stream_verdict); +out: return ret; }