Re: [PATCH] rxrpc: fix bad unlock balance in rxrpc_do_sendmsg
From: Hawkins Jiawei
Date: Mon Aug 22 2022 - 09:05:36 EST
On Mon, 22 Aug 2022 at 19:30, Hawkins Jiawei <yin31149@xxxxxxxxx> wrote:
>
> On Mon, 22 Aug 2022 at 16:48, David Howells <dhowells@xxxxxxxxxx> wrote:
> >
> > Hawkins Jiawei <yin31149@xxxxxxxxx> wrote:
> >
> > > - if (mutex_lock_interruptible(&call->user_mutex) < 0)
> > > + if (mutex_lock_interruptible(&call->user_mutex) < 0) {
> > > + mutex_lock(&call->user_mutex);
> >
> > Yeah, as Khalid points out that kind of makes the interruptible lock
> > pointless. Either rxrpc_send_data() needs to return a separate indication
> > that we returned without the lock held or it needs to always drop the lock on
> > error (at least for ERESTARTSYS/EINTR) which can be checked for higher up.
> Hi David,
>
> For second option, I think it may meet some difficulty, because we
> cannot figure out whether rxrpc_send_data() meets lock error.
> To be more specific, rxrpc_send_data() may still returns the number
> it has copied even rxrpc_send_data() meets lock error, if
> rxrpc_send_data() has successfully dealed some data.(Please correct me
> if I am wrong)
>
> So I think the first option seems better. I wonder if we can add an
> argument in rxrpc_send_data() as an indication you pointed out? Maybe:
>
> diff --git a/net/rxrpc/sendmsg.c b/net/rxrpc/sendmsg.c
> index 1d38e279e2ef..0801325a7c7f 100644
> --- a/net/rxrpc/sendmsg.c
> +++ b/net/rxrpc/sendmsg.c
> @@ -284,13 +284,18 @@ static int rxrpc_queue_packet(struct rxrpc_sock *rx, struct rxrpc_call *call,
>
> /*
> * send data through a socket
> + * @holding_mutex: rxrpc_send_data() will assign this pointer with True
> + * if functions still holds the call user access mutex when returned to caller.
> + * This argument can be NULL, which will effect nothing.
> + *
> * - must be called in process context
> * - The caller holds the call user access mutex, but not the socket lock.
> */
> static int rxrpc_send_data(struct rxrpc_sock *rx,
> struct rxrpc_call *call,
> struct msghdr *msg, size_t len,
> - rxrpc_notify_end_tx_t notify_end_tx)
> + rxrpc_notify_end_tx_t notify_end_tx,
> + bool *holding_mutex)
> {
> struct rxrpc_skb_priv *sp;
> struct sk_buff *skb;
> @@ -299,6 +304,9 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
> bool more;
> int ret, copied;
>
> + if (holding_mutex)
> + *holding_mutex = true;
> +
> timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
>
> /* this should be in poll */
> @@ -338,8 +346,11 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
> ret = rxrpc_wait_for_tx_window(rx, call,
> &timeo,
> msg->msg_flags & MSG_WAITALL);
> - if (ret < 0)
> + if (ret < 0) {
> + if (holding_mutex)
> + *holding_mutex = false;
> goto maybe_error;
> + }
> }
>
> /* Work out the maximum size of a packet. Assume that
> @@ -630,6 +641,7 @@ int rxrpc_do_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg, size_t len)
> struct rxrpc_call *call;
> unsigned long now, j;
> int ret;
> + bool holding_user_mutex;
>
> struct rxrpc_send_params p = {
> .call.tx_total_len = -1,
> @@ -747,7 +759,9 @@ int rxrpc_do_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg, size_t len)
> /* Reply phase not begun or not complete for service call. */
> ret = -EPROTO;
> } else {
> - ret = rxrpc_send_data(rx, call, msg, len, NULL);
> + ret = rxrpc_send_data(rx, call, msg, len, NULL, &holding_user_mutex);
> + if (!holding_user_mutex)
> + goto error_put;
> }
>
> out_put_unlock:
> @@ -796,7 +810,7 @@ int rxrpc_kernel_send_data(struct socket *sock, struct rxrpc_call *call,
> case RXRPC_CALL_SERVER_ACK_REQUEST:
> case RXRPC_CALL_SERVER_SEND_REPLY:
> ret = rxrpc_send_data(rxrpc_sk(sock->sk), call, msg, len,
> - notify_end_tx);
> + notify_end_tx, NULL);
> break;
> case RXRPC_CALL_COMPLETE:
> read_lock_bh(&call->state_lock);
>
> After applying the above patch, kernel still panic, but seems not the
> bad unlock balance bug before. yet I am not sure if this is the same bug you
> mentioned. Kernel output as below:
> [ 39.115966][ T6508] ====================================
> [ 39.116940][ T6508] WARNING: syz/6508 still has locks held!
> [ 39.117978][ T6508] 6.0.0-rc1-00066-g3b06a2755758-dirty #186 Not tainted
> [ 39.119353][ T6508] ------------------------------------
> [ 39.120321][ T6508] 1 lock held by syz/6508:
> [ 39.121122][ T6508] #0: ffff88801f472b20 (&call->user_mutex){....}-{3:3}0
> [ 39.123014][ T6508]
> [ 39.123014][ T6508] stack backtrace:
> [ 39.123925][ T6508] CPU: 0 PID: 6508 Comm: syz Not tainted 6.0.0-rc1-00066
> [ 39.125304][ T6508] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)4
> [ 39.125304][ T6508] Call Trace:
> [ 39.125304][ T6508] <TASK>
> [ 39.125304][ T6508] dump_stack_lvl+0x8e/0xdd
> [ 39.125304][ T6508] get_signal+0x1866/0x24d0
> [ 39.125304][ T6508] ? lock_acquire+0x172/0x310
> [ 39.125304][ T6508] ? exit_signals+0x7b0/0x7b0
> [ 39.125304][ T6508] arch_do_signal_or_restart+0x82/0x23f0
> [ 39.125304][ T6508] ? __sanitizer_cov_trace_pc+0x1a/0x40
> [ 39.125304][ T6508] ? __fget_light+0x20d/0x270
> [ 39.125304][ T6508] ? get_sigframe_size+0x10/0x10
> [ 39.125304][ T6508] ? __sanitizer_cov_trace_pc+0x1a/0x40
> [ 39.125304][ T6508] ? __sys_sendmsg+0x11a/0x1c0
> [ 39.125304][ T6508] ? __sys_sendmsg_sock+0x30/0x30
> [ 39.125304][ T6508] exit_to_user_mode_prepare+0x146/0x1b0
> [ 39.125304][ T6508] syscall_exit_to_user_mode+0x12/0x30
> [ 39.125304][ T6508] do_syscall_64+0x42/0xb0
> [ 39.125304][ T6508] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> [ 39.125304][ T6508] RIP: 0033:0x44fbad
> [ 39.125304][ T6508] Code: c3 e8 97 29 00 00 0f 1f 80 00 00 00 00 f3 0f 1e8
> [ 39.125304][ T6508] RSP: 002b:00007f4b8ae22d48 EFLAGS: 00000246 ORIG_RAX:e
> [ 39.125304][ T6508] RAX: fffffffffffffffc RBX: 0000000000000000 RCX: 0000d
> [ 39.125304][ T6508] RDX: 0000000000000186 RSI: 0000000020000000 RDI: 00003
> [ 39.125304][ T6508] RBP: 00007f4b8ae22d80 R08: 00007f4b8ae23700 R09: 00000
> [ 39.125304][ T6508] R10: 00007f4b8ae23700 R11: 0000000000000246 R12: 0000e
> [ 39.125304][ T6508] R13: 00007ffe483304af R14: 00007ffe48330550 R15: 00000
> [ 39.125304][ T6508] </TASK>
> ====================================
>
> I will make a deeper look and try to patch it.
The cause is that patch assigns False to pointer holding_mutex in
rxrpc_send_data() by only juding whether the return value from
rxrpc_wait_for_tx_window() is less than 0, yet this is not correct.
So we should just only assign False to holding_mutex when
unlocking the call->user_mutex in rxrpc_wait_for_tx_window_intr().
Maybe:
diff --git a/net/rxrpc/sendmsg.c b/net/rxrpc/sendmsg.c
index 1d38e279e2ef..1050cc2f5c89 100644
--- a/net/rxrpc/sendmsg.c
+++ b/net/rxrpc/sendmsg.c
@@ -33,11 +33,16 @@ static bool rxrpc_check_tx_space(struct rxrpc_call *call, rxrpc_seq_t *_tx_win)
}
/*
+ * @holding_mutex: An indication whether caller can still holds
+ * the call->user_mutex when returned to caller.
+ * This argument can be NULL, which will effect nothing.
+ *
* Wait for space to appear in the Tx queue or a signal to occur.
*/
static int rxrpc_wait_for_tx_window_intr(struct rxrpc_sock *rx,
struct rxrpc_call *call,
- long *timeo)
+ long *timeo,
+ bool *holding_mutex)
{
for (;;) {
set_current_state(TASK_INTERRUPTIBLE);
@@ -53,8 +58,11 @@ static int rxrpc_wait_for_tx_window_intr(struct rxrpc_sock *rx,
trace_rxrpc_transmit(call, rxrpc_transmit_wait);
mutex_unlock(&call->user_mutex);
*timeo = schedule_timeout(*timeo);
- if (mutex_lock_interruptible(&call->user_mutex) < 0)
+ if (mutex_lock_interruptible(&call->user_mutex) < 0) {
+ if (holding_mutex)
+ *holding_mutex = false;
return sock_intr_errno(*timeo);
+ }
}
}
@@ -121,13 +129,18 @@ static int rxrpc_wait_for_tx_window_nonintr(struct rxrpc_sock *rx,
}
/*
+ * @holding_mutex: An indication whether caller can still holds
+ * the call->user_mutex when returned to caller.
+ * This argument can be NULL, which will effect nothing.
+ *
* wait for space to appear in the transmit/ACK window
* - caller holds the socket locked
*/
static int rxrpc_wait_for_tx_window(struct rxrpc_sock *rx,
struct rxrpc_call *call,
long *timeo,
- bool waitall)
+ bool waitall,
+ bool *holding_mutex)
{
DECLARE_WAITQUEUE(myself, current);
int ret;
@@ -142,7 +155,7 @@ static int rxrpc_wait_for_tx_window(struct rxrpc_sock *rx,
if (waitall)
ret = rxrpc_wait_for_tx_window_waitall(rx, call);
else
- ret = rxrpc_wait_for_tx_window_intr(rx, call, timeo);
+ ret = rxrpc_wait_for_tx_window_intr(rx, call, timeo, holding_mutex);
break;
case RXRPC_PREINTERRUPTIBLE:
case RXRPC_UNINTERRUPTIBLE:
@@ -284,13 +297,19 @@ static int rxrpc_queue_packet(struct rxrpc_sock *rx, struct rxrpc_call *call,
/*
* send data through a socket
+ *
+ * @holding_mutex: An indication whether caller can still holds
+ * the call->user_mutex when returned to caller.
+ * This argument can be NULL, which will effect nothing.
+ *
* - must be called in process context
* - The caller holds the call user access mutex, but not the socket lock.
*/
static int rxrpc_send_data(struct rxrpc_sock *rx,
struct rxrpc_call *call,
struct msghdr *msg, size_t len,
- rxrpc_notify_end_tx_t notify_end_tx)
+ rxrpc_notify_end_tx_t notify_end_tx,
+ bool *holding_mutex)
{
struct rxrpc_skb_priv *sp;
struct sk_buff *skb;
@@ -299,6 +318,13 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
bool more;
int ret, copied;
+ /*
+ * The caller holds the call->user_mutex when calls
+ * rxrpc_send_data(), so initial it with True
+ */
+ if (holding_mutex)
+ *holding_mutex = true;
+
timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
/* this should be in poll */
@@ -337,7 +363,8 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
goto maybe_error;
ret = rxrpc_wait_for_tx_window(rx, call,
&timeo,
- msg->msg_flags & MSG_WAITALL);
+ msg->msg_flags & MSG_WAITALL,
+ holding_mutex);
if (ret < 0)
goto maybe_error;
}
@@ -630,6 +657,7 @@ int rxrpc_do_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg, size_t len)
struct rxrpc_call *call;
unsigned long now, j;
int ret;
+ bool holding_user_mutex;
struct rxrpc_send_params p = {
.call.tx_total_len = -1,
@@ -747,7 +775,9 @@ int rxrpc_do_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg, size_t len)
/* Reply phase not begun or not complete for service call. */
ret = -EPROTO;
} else {
- ret = rxrpc_send_data(rx, call, msg, len, NULL);
+ ret = rxrpc_send_data(rx, call, msg, len, NULL, &holding_user_mutex);
+ if (!holding_user_mutex)
+ goto error_put;
}
out_put_unlock:
@@ -796,7 +826,7 @@ int rxrpc_kernel_send_data(struct socket *sock, struct rxrpc_call *call,
case RXRPC_CALL_SERVER_ACK_REQUEST:
case RXRPC_CALL_SERVER_SEND_REPLY:
ret = rxrpc_send_data(rxrpc_sk(sock->sk), call, msg, len,
- notify_end_tx);
+ notify_end_tx, NULL);
break;
case RXRPC_CALL_COMPLETE:
read_lock_bh(&call->state_lock);
Reproducer did not trigger any issue locally. I will propose a test by
syzbot. Maybe I will send v2 patch if patch can pass the syzbot tesing.