6.6-stable review patch. If anyone has any objections, please let me know.
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From: Michal Luczaj mhal@rbox.co
commit 041933a1ec7b4173a8e638cae4f8e394331d7e54 upstream.
GC attempts to explicitly drop oob_skb's reference before purging the hit list.
The problem is with embryos: kfree_skb(u->oob_skb) is never called on an embryo socket.
The python script below [0] sends a listener's fd to its embryo as OOB data. While GC does collect the embryo's queue, it fails to drop the OOB skb's refcount. The skb which was in embryo's receive queue stays as unix_sk(sk)->oob_skb and keeps the listener's refcount [1].
Tell GC to dispose embryo's oob_skb.
[0]: from array import array from socket import *
addr = '\x00unix-oob' lis = socket(AF_UNIX, SOCK_STREAM) lis.bind(addr) lis.listen(1)
s = socket(AF_UNIX, SOCK_STREAM) s.connect(addr) scm = (SOL_SOCKET, SCM_RIGHTS, array('i', [lis.fileno()])) s.sendmsg([b'x'], [scm], MSG_OOB) lis.close()
[1] $ grep unix-oob /proc/net/unix $ ./unix-oob.py $ grep unix-oob /proc/net/unix 0000000000000000: 00000002 00000000 00000000 0001 02 0 @unix-oob 0000000000000000: 00000002 00000000 00010000 0001 01 6072 @unix-oob
Fixes: 4090fa373f0e ("af_unix: Replace garbage collection algorithm.") Signed-off-by: Michal Luczaj mhal@rbox.co Reviewed-by: Kuniyuki Iwashima kuniyu@amazon.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Lee Jones lee@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/unix/garbage.c | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-)
--- a/net/unix/garbage.c +++ b/net/unix/garbage.c @@ -342,6 +342,18 @@ enum unix_recv_queue_lock_class { U_RECVQ_LOCK_EMBRYO, };
+static void unix_collect_queue(struct unix_sock *u, struct sk_buff_head *hitlist) +{ + skb_queue_splice_init(&u->sk.sk_receive_queue, hitlist); + +#if IS_ENABLED(CONFIG_AF_UNIX_OOB) + if (u->oob_skb) { + WARN_ON_ONCE(skb_unref(u->oob_skb)); + u->oob_skb = NULL; + } +#endif +} + static void unix_collect_skb(struct list_head *scc, struct sk_buff_head *hitlist) { struct unix_vertex *vertex; @@ -365,18 +377,11 @@ static void unix_collect_skb(struct list
/* listener -> embryo order, the inversion never happens. */ spin_lock_nested(&embryo_queue->lock, U_RECVQ_LOCK_EMBRYO); - skb_queue_splice_init(embryo_queue, hitlist); + unix_collect_queue(unix_sk(skb->sk), hitlist); spin_unlock(&embryo_queue->lock); } } else { - skb_queue_splice_init(queue, hitlist); - -#if IS_ENABLED(CONFIG_AF_UNIX_OOB) - if (u->oob_skb) { - kfree_skb(u->oob_skb); - u->oob_skb = NULL; - } -#endif + unix_collect_queue(u, hitlist); }
spin_unlock(&queue->lock);