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.
Reported-by: xingwei lee <xrivendell7@xxxxxxxxx>
Reported-by: yue sun <samsun1006219@xxxxxxxxx>
Reported-by: syzbot+bc922f476bd65abbd466@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-and-tested-by: syzbot+d4066896495db380182e@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=d4066896495db380182e
Closes: https://syzkaller.appspot.com/bug?extid=bc922f476bd65abbd466
Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
---
Cc: John Fastabend <john.fastabend@xxxxxxxxx>
Cc: Edward Adam Davis <eadavis@xxxxxx>
Cc: Shung-Hsi Yu <shung-hsi.yu@xxxxxxxx>
---
net/core/sock_map.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 27d733c0f65e..8598466a3805 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -411,6 +411,9 @@ static int __sock_map_delete(struct bpf_stab *stab, struct sock *sk_test,
struct sock *sk;
int err = 0;
+ if (irqs_disabled())
+ return -EOPNOTSUPP; /* locks here are hardirq-unsafe */
+
spin_lock_bh(&stab->lock);
sk = *psk;
if (!sk_test || sk_test == sk)
@@ -933,6 +936,9 @@ static long sock_hash_delete_elem(struct bpf_map *map, void *key)
struct bpf_shtab_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);
--
2.44.0
