Re: [RESEND PATCH] ipc/mqueue: fix potential sleeping issue in mqueue_flush_file

From: Jan Kara
Date: Mon Dec 18 2023 - 08:14:08 EST

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[CCed some networking people & netdev list since this is closely related to
networking]

On Mon 18-12-23 11:06:24, Zhengchao Shao wrote:
> I analyze the potential sleeping issue of the following processes:
> Thread A Thread B
> ... netlink_create //create sock
> do_mq_notify ...
> sock = netlink_getsockbyfilp ... //hold sock
> info->notify_sock = sock; ...
> ... netlink_sendmsg
> ... skb = netlink_alloc_large_skb //skb->head is vmalloced
> ... netlink_unicast
> ... sk = netlink_getsockbyportid
> ... netlink_sendskb
> ... __netlink_sendskb
> ... skb_queue_tail //put skb to sk_receive_queue
> mqueue_flush_file
> spin_lock
> remove_notification
> netlink_sendskb
> sock_put //put sock
> sk_free
> ...
> __sk_destruct
> netlink_sock_destruct
> skb_queue_purge //get skb from sk_receive_queue
> ...
> __skb_queue_purge_reason
> kfree_skb_reason
> __kfree_skb
> ...
> skb_release_all
> skb_release_head_state
> netlink_skb_destructor
> vfree(skb->head) //sleeping while holding spinlock
>
> In netlink_sendmsg, if the memory pointed to by skb->head is allocated by
> vmalloc, and is put to sk_receive_queue queue, also the skb is not freed.
> When the mqueue executes flush, the sleeping bug will occur. Use mutex
> lock instead of spin lock in mqueue_flush_file.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Zhengchao Shao <shaozhengchao@xxxxxxxxxx>

I guess you are not getting answers because ipc/mqueue.c has no clear
maintainer and at least I know nothing about mqueue and only very little
about netlink which is also involved here. Do I get it right this was
spotted by some checker, not really causing problems in the wild?

Another question (and this is why I've involved the networking people): Is
it really possible that we end up calling sk_free() from under
mqueue_flush_file() - at the time this is called we are closing the file
but it is not closed yet which means the socket inode is pretty much alive
which I'd *think* means there is still somebody holding socket reference
and thus sock_put() will not drop the last socket reference... Am I missing
something?

Honza

> ---
> ipc/mqueue.c | 48 ++++++++++++++++++++++++------------------------
> 1 file changed, 24 insertions(+), 24 deletions(-)
>
> diff --git a/ipc/mqueue.c b/ipc/mqueue.c
> index 5eea4dc0509e..f6f92e3f82e4 100644
> --- a/ipc/mqueue.c
> +++ b/ipc/mqueue.c
> @@ -118,9 +118,9 @@ struct posix_msg_tree_node {
> * Solution: use _release and _acquire barriers.
> *
> * 3) There is intentionally no barrier when setting current->state
> - * to TASK_INTERRUPTIBLE: spin_unlock(&info->lock) provides the
> + * to TASK_INTERRUPTIBLE: mutex_unlock(&info->lock) provides the
> * release memory barrier, and the wakeup is triggered when holding
> - * info->lock, i.e. spin_lock(&info->lock) provided a pairing
> + * info->lock, i.e. mutex_lock(&info->lock) provided a pairing
> * acquire memory barrier.
> */
>
> @@ -132,7 +132,7 @@ struct ext_wait_queue { /* queue of sleeping tasks */
> };
>
> struct mqueue_inode_info {
> - spinlock_t lock;
> + struct mutex lock;
> struct inode vfs_inode;
> wait_queue_head_t wait_q;
>
> @@ -312,7 +312,7 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
> inode->i_size = FILENT_SIZE;
> /* mqueue specific info */
> info = MQUEUE_I(inode);
> - spin_lock_init(&info->lock);
> + mutex_init(&info->lock);
> init_waitqueue_head(&info->wait_q);
> INIT_LIST_HEAD(&info->e_wait_q[0].list);
> INIT_LIST_HEAD(&info->e_wait_q[1].list);
> @@ -523,11 +523,11 @@ static void mqueue_evict_inode(struct inode *inode)
>
> ipc_ns = get_ns_from_inode(inode);
> info = MQUEUE_I(inode);
> - spin_lock(&info->lock);
> + mutex_lock(&info->lock);
> while ((msg = msg_get(info)) != NULL)
> list_add_tail(&msg->m_list, &tmp_msg);
> kfree(info->node_cache);
> - spin_unlock(&info->lock);
> + mutex_unlock(&info->lock);
>
> list_for_each_entry_safe(msg, nmsg, &tmp_msg, m_list) {
> list_del(&msg->m_list);
> @@ -640,7 +640,7 @@ static ssize_t mqueue_read_file(struct file *filp, char __user *u_data,
> char buffer[FILENT_SIZE];
> ssize_t ret;
>
> - spin_lock(&info->lock);
> + mutex_lock(&info->lock);
> snprintf(buffer, sizeof(buffer),
> "QSIZE:%-10lu NOTIFY:%-5d SIGNO:%-5d NOTIFY_PID:%-6d\n",
> info->qsize,
> @@ -649,7 +649,7 @@ static ssize_t mqueue_read_file(struct file *filp, char __user *u_data,
> info->notify.sigev_notify == SIGEV_SIGNAL) ?
> info->notify.sigev_signo : 0,
> pid_vnr(info->notify_owner));
> - spin_unlock(&info->lock);
> + mutex_unlock(&info->lock);
> buffer[sizeof(buffer)-1] = '\0';
>
> ret = simple_read_from_buffer(u_data, count, off, buffer,
> @@ -665,11 +665,11 @@ static int mqueue_flush_file(struct file *filp, fl_owner_t id)
> {
> struct mqueue_inode_info *info = MQUEUE_I(file_inode(filp));
>
> - spin_lock(&info->lock);
> + mutex_lock(&info->lock);
> if (task_tgid(current) == info->notify_owner)
> remove_notification(info);
>
> - spin_unlock(&info->lock);
> + mutex_unlock(&info->lock);
> return 0;
> }
>
> @@ -680,13 +680,13 @@ static __poll_t mqueue_poll_file(struct file *filp, struct poll_table_struct *po
>
> poll_wait(filp, &info->wait_q, poll_tab);
>
> - spin_lock(&info->lock);
> + mutex_lock(&info->lock);
> if (info->attr.mq_curmsgs)
> retval = EPOLLIN | EPOLLRDNORM;
>
> if (info->attr.mq_curmsgs < info->attr.mq_maxmsg)
> retval |= EPOLLOUT | EPOLLWRNORM;
> - spin_unlock(&info->lock);
> + mutex_unlock(&info->lock);
>
> return retval;
> }
> @@ -724,7 +724,7 @@ static int wq_sleep(struct mqueue_inode_info *info, int sr,
> /* memory barrier not required, we hold info->lock */
> __set_current_state(TASK_INTERRUPTIBLE);
>
> - spin_unlock(&info->lock);
> + mutex_unlock(&info->lock);
> time = schedule_hrtimeout_range_clock(timeout, 0,
> HRTIMER_MODE_ABS, CLOCK_REALTIME);
>
> @@ -734,7 +734,7 @@ static int wq_sleep(struct mqueue_inode_info *info, int sr,
> retval = 0;
> goto out;
> }
> - spin_lock(&info->lock);
> + mutex_lock(&info->lock);
>
> /* we hold info->lock, so no memory barrier required */
> if (READ_ONCE(ewp->state) == STATE_READY) {
> @@ -752,7 +752,7 @@ static int wq_sleep(struct mqueue_inode_info *info, int sr,
> }
> list_del(&ewp->list);
> out_unlock:
> - spin_unlock(&info->lock);
> + mutex_unlock(&info->lock);
> out:
> return retval;
> }
> @@ -1125,7 +1125,7 @@ static int do_mq_timedsend(mqd_t mqdes, const char __user *u_msg_ptr,
> if (!info->node_cache)
> new_leaf = kmalloc(sizeof(*new_leaf), GFP_KERNEL);
>
> - spin_lock(&info->lock);
> + mutex_lock(&info->lock);
>
> if (!info->node_cache && new_leaf) {
> /* Save our speculative allocation into the cache */
> @@ -1166,7 +1166,7 @@ static int do_mq_timedsend(mqd_t mqdes, const char __user *u_msg_ptr,
> simple_inode_init_ts(inode);
> }
> out_unlock:
> - spin_unlock(&info->lock);
> + mutex_unlock(&info->lock);
> wake_up_q(&wake_q);
> out_free:
> if (ret)
> @@ -1230,7 +1230,7 @@ static int do_mq_timedreceive(mqd_t mqdes, char __user *u_msg_ptr,
> if (!info->node_cache)
> new_leaf = kmalloc(sizeof(*new_leaf), GFP_KERNEL);
>
> - spin_lock(&info->lock);
> + mutex_lock(&info->lock);
>
> if (!info->node_cache && new_leaf) {
> /* Save our speculative allocation into the cache */
> @@ -1242,7 +1242,7 @@ static int do_mq_timedreceive(mqd_t mqdes, char __user *u_msg_ptr,
>
> if (info->attr.mq_curmsgs == 0) {
> if (f.file->f_flags & O_NONBLOCK) {
> - spin_unlock(&info->lock);
> + mutex_unlock(&info->lock);
> ret = -EAGAIN;
> } else {
> wait.task = current;
> @@ -1261,7 +1261,7 @@ static int do_mq_timedreceive(mqd_t mqdes, char __user *u_msg_ptr,
>
> /* There is now free space in queue. */
> pipelined_receive(&wake_q, info);
> - spin_unlock(&info->lock);
> + mutex_unlock(&info->lock);
> wake_up_q(&wake_q);
> ret = 0;
> }
> @@ -1391,7 +1391,7 @@ static int do_mq_notify(mqd_t mqdes, const struct sigevent *notification)
> info = MQUEUE_I(inode);
>
> ret = 0;
> - spin_lock(&info->lock);
> + mutex_lock(&info->lock);
> if (notification == NULL) {
> if (info->notify_owner == task_tgid(current)) {
> remove_notification(info);
> @@ -1424,7 +1424,7 @@ static int do_mq_notify(mqd_t mqdes, const struct sigevent *notification)
> info->notify_user_ns = get_user_ns(current_user_ns());
> inode_set_atime_to_ts(inode, inode_set_ctime_current(inode));
> }
> - spin_unlock(&info->lock);
> + mutex_unlock(&info->lock);
> out_fput:
> fdput(f);
> out:
> @@ -1470,7 +1470,7 @@ static int do_mq_getsetattr(int mqdes, struct mq_attr *new, struct mq_attr *old)
> inode = file_inode(f.file);
> info = MQUEUE_I(inode);
>
> - spin_lock(&info->lock);
> + mutex_lock(&info->lock);
>
> if (old) {
> *old = info->attr;
> @@ -1488,7 +1488,7 @@ static int do_mq_getsetattr(int mqdes, struct mq_attr *new, struct mq_attr *old)
> inode_set_atime_to_ts(inode, inode_set_ctime_current(inode));
> }
>
> - spin_unlock(&info->lock);
> + mutex_unlock(&info->lock);
> fdput(f);
> return 0;
> }
> --
> 2.34.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR

Next message: Ilpo Järvinen: "Re: [PATCH v2] platform/x86: thinkpad_acpi: fix for incorrect fan reporting on some ThinkPad systems"
Previous message: Krzysztof Kozlowski: "[PATCH] dt-bindings: phy: qcom,sc8280xp-qmp-usb43dp-phy: fix path to header"
Next in thread: shaozhengchao: "Re: [RESEND PATCH] ipc/mqueue: fix potential sleeping issue in mqueue_flush_file"
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