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Date: Wed, 12 Jan 2022 10:13:53 +0800 From: Hangyu Hua <hbh25y@...il.com> To: Eric Dumazet <eric.dumazet@...il.com>, jreuter@...na.de, ralf@...ux-mips.org, davem@...emloft.net, kuba@...nel.org Cc: linux-hams@...r.kernel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH net] ax25: use after free in ax25_connect I try to use ax25_release to trigger this bug like this: ax25_release ax25_connect lock_sock(sk); -----------------------------sk = sock->sk; -----------------------------ax25 = sk_to_ax25(sk); ax25_destroy_socket(ax25); release_sock(sk); -----------------------------lock_sock(sk); -----------------------------use ax25 again But i failed beacause their have large speed difference. And i don't have a physical device to test other function in ax25. Anyway, i still think there will have a function to trigger this race condition like ax25_destroy_timer. Beacause Any ohter functions in ax25_proto_ops like ax25_bind protect ax25_sock by lock_sock(sk). Thanks. On 2022/1/12 上午4:56, Eric Dumazet wrote: > > On 1/10/22 20:20, Hangyu Hua wrote: >> sk_to_ax25(sk) needs to be called after lock_sock(sk) to avoid UAF >> caused by a race condition. > > Can you describe what race condition you have found exactly ? > > sk pointer can not change. > > >> Signed-off-by: Hangyu Hua <hbh25y@...il.com> >> --- >> net/ax25/af_ax25.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c >> index cfca99e295b8..c5d62420a2a8 100644 >> --- a/net/ax25/af_ax25.c >> +++ b/net/ax25/af_ax25.c >> @@ -1127,7 +1127,7 @@ static int __must_check ax25_connect(struct >> socket *sock, >> struct sockaddr *uaddr, int addr_len, int flags) >> { >> struct sock *sk = sock->sk; >> - ax25_cb *ax25 = sk_to_ax25(sk), *ax25t; >> + ax25_cb *ax25, *ax25t; >> struct full_sockaddr_ax25 *fsa = (struct full_sockaddr_ax25 >> *)uaddr; >> ax25_digi *digi = NULL; >> int ct = 0, err = 0; >> @@ -1155,6 +1155,8 @@ static int __must_check ax25_connect(struct >> socket *sock, >> lock_sock(sk); >> + ax25 = sk_to_ax25(sk); >> + >> /* deal with restarts */ >> if (sock->state == SS_CONNECTING) { >> switch (sk->sk_state) {
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