Thanks for the fix.
Using net/smc as prefix in subject is preferred.
On Sat, Apr 08, 2023 at 11:49:43AM -0700, Kuniyuki Iwashima wrote:
> With Eric's ref tracker, syzbot finally found a repro for
> use-after-free in tcp_write_timer_handler() by kernel TCP
> sockets. [0]
>
> If SMC creates a kernel socket in __smc_create(), the kernel
> socket is supposed to be freed in smc_clcsock_release() by
> calling sock_release() when we close() the parent SMC socket.
>
> However, at the end of smc_clcsock_release(), the kernel
> socket's sk_state might not be TCP_CLOSE. This means that
> we have not called inet_csk_destroy_sock() in __tcp_close()
> and have not stopped the TCP timers.
>
> The kernel socket's TCP timers can be fired later, so we
> need to hold a refcnt for net as we do for MPTCP subflows
> in mptcp_subflow_create_socket().
Agreed.
>
> [0]:
> leaked reference.
> sk_alloc (./include/net/net_namespace.h:335 net/core/sock.c:2108)
> inet_create (net/ipv4/af_inet.c:319 net/ipv4/af_inet.c:244)
> __sock_create (net/socket.c:1546)
> smc_create (net/smc/af_smc.c:3269 net/smc/af_smc.c:3284)
> __sock_create (net/socket.c:1546)
> __sys_socket (net/socket.c:1634 net/socket.c:1618 net/socket.c:1661)
> __x64_sys_socket (net/socket.c:1672)
> do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)
> ==================================================================
> BUG: KASAN: slab-use-after-free in tcp_write_timer_handler (net/ipv4/tcp_timer.c:378 net/ipv4/tcp_timer.c:624 net/ipv4/tcp_timer.c:594)
> Read of size 1 at addr ffff888052b65e0d by task syzrepro/18091
>
> CPU: 0 PID: 18091 Comm: syzrepro Tainted: G W 6.3.0-rc4-01174-gb5d54eb5899a #7
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-1.amzn2022.0.1 04/01/2014
> Call Trace:
> <IRQ>
> dump_stack_lvl (lib/dump_stack.c:107)
> print_report (mm/kasan/report.c:320 mm/kasan/report.c:430)
> kasan_report (mm/kasan/report.c:538)
> tcp_write_timer_handler (net/ipv4/tcp_timer.c:378 net/ipv4/tcp_timer.c:624 net/ipv4/tcp_timer.c:594)
> tcp_write_timer (./include/linux/spinlock.h:390 net/ipv4/tcp_timer.c:643)
> call_timer_fn (./arch/x86/include/asm/jump_label.h:27 ./include/linux/jump_label.h:207 ./include/trace/events/timer.h:127 kernel/time/timer.c:1701)
> __run_timers.part.0 (kernel/time/timer.c:1752 kernel/time/timer.c:2022)
> run_timer_softirq (kernel/time/timer.c:2037)
> __do_softirq (./arch/x86/include/asm/jump_label.h:27 ./include/linux/jump_label.h:207 ./include/trace/events/irq.h:142 kernel/softirq.c:572)
> __irq_exit_rcu (kernel/softirq.c:445 kernel/softirq.c:650)
> irq_exit_rcu (kernel/softirq.c:664)
> sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1107 (discriminator 14))
> </IRQ>
>
> Fixes: ac7138746e14 ("smc: establish new socket family")
> Reported-by: syzbot+7e1e1bdb852961150198@xxxxxxxxxxxxxxxxxxxxxxxxx
> Link: https://lore.kernel.org/netdev/000000000000a3f51805f8bcc43a@xxxxxxxxxx/
> Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
LGTM.
Reviewed-by: Tony Lu <tonylu@xxxxxxxxxxxxxxxxx>
> ---
> net/smc/af_smc.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
> index c6b4a62276f6..50c38b624f77 100644
> --- a/net/smc/af_smc.c
> +++ b/net/smc/af_smc.c
> @@ -3270,6 +3270,17 @@ static int __smc_create(struct net *net, struct socket *sock, int protocol,
> sk_common_release(sk);
> goto out;
> }
> +
> + /* smc_clcsock_release() does not wait smc->clcsock->sk's
> + * destruction; its sk_state might not be TCP_CLOSE after
> + * smc->sk is close()d, and TCP timers can be fired later,
> + * which need net ref.
> + */
> + sk = smc->clcsock->sk;
> + __netns_tracker_free(net, &sk->ns_tracker, false);
> + sk->sk_net_refcnt = 1;
> + get_net_track(net, &sk->ns_tracker, GFP_KERNEL);
> + sock_inuse_add(net, 1);
> } else {
> smc->clcsock = clcsock;
> }
> --
> 2.30.2
