[PATCH 5.4 148/215] bpf, sockmap: Prevent lock inversion deadlock in map delete elem

Greg Kroah-Hartman
2024-04-11T10:21:37Z

From: Jakub Sitnicki <jakub@cloudflare.com>

commit ff91059932401894e6c86341915615c5eb0eca48 upstream.

syzkaller started using corpuses where a BPF tracing program deletes
elements from a sockmap/sockhash map. Because BPF tracing programs can be
invoked from any interrupt context, locks taken during a map_delete_elem
operation must be hardirq-safe. Otherwise a deadlock due to lock inversion
is possible, as reported by lockdep:

CPU0 CPU1
---- ----
lock(&htab->buckets[i].lock);
local_irq_disable();
lock(&host->lock);
lock(&htab->buckets[i].lock);
<Interrupt>
lock(&host->lock);

Locks in sockmap are hardirq-unsafe by design. We expects elements to be
deleted from sockmap/sockhash only in task (normal) context with interrupts
enabled, or in softirq context.

Detect when map_delete_elem operation is invoked from a context which is
_not_ hardirq-unsafe, that is interrupts are disabled, and bail out with an
error.

Note that map updates are not affected by this issue. BPF verifier does not
allow updating sockmap/sockhash from a BPF tracing program today.

Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
Reported-by: xingwei lee <xrivendell7@gmail.com>
Reported-by: yue sun <samsun1006219@gmail.com>
Reported-by: syzbot+bc922f476bd65abbd466@syzkaller.appspotmail.com
Reported-by: syzbot+d4066896495db380182e@syzkaller.appspotmail.com
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: syzbot+d4066896495db380182e@syzkaller.appspotmail.com
Acked-by: John Fastabend <john.fastabend@gmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=d4066896495db380182e
Closes: https://syzkaller.appspot.com/bug?extid=bc922f476bd65abbd466
Link: https://lore.kernel.org/bpf/20240402104621.1050319-1-jakub@cloudflare.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/sock_map.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -321,6 +321,9 @@ static int __sock_map_delete(struct bpf_
struct sock *sk;
int err = 0;

+ if (irqs_disabled())
+ return -EOPNOTSUPP; /* locks here are hardirq-unsafe */
+
raw_spin_lock_bh(&stab->lock);
sk = *psk;
if (!sk_test || sk_test == sk)
@@ -654,6 +657,9 @@ static int sock_hash_delete_elem(struct
struct bpf_htab_elem *elem;
int ret = -ENOENT;

+ if (irqs_disabled())
+ return -EOPNOTSUPP; /* locks here are hardirq-unsafe */
+
hash = sock_hash_bucket_hash(key, key_size);
bucket = sock_hash_select_bucket(htab, hash);