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https://github.com/brain-hackers/linux-brain.git
synced 2024-06-09 15:26:21 +09:00
[PATCH] splice: fix problems with sys_tee()
Several issues noticed/fixed: - We cannot reliably block in link_pipe() while holding both input and output mutexes. So do preparatory checks before locking down both mutexes and doing the link. - The ipipe->nrbufs vs i check was bad, because we could have dropped the ipipe lock in-between. This causes us to potentially look at unknown buffers if we were racing with someone else reading this pipe. Signed-off-by: Jens Axboe <axboe@suse.de>
This commit is contained in:
Jens Axboe
parent
b3cf257623
commit
aadd06e5c5
240
fs/splice.c
240
fs/splice.c
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@ -1306,6 +1306,85 @@ asmlinkage long sys_splice(int fd_in, loff_t __user *off_in,
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return error;
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}
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/*
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* Make sure there's data to read. Wait for input if we can, otherwise
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* return an appropriate error.
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*/
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static int link_ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
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{
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int ret;
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/*
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* Check ->nrbufs without the inode lock first. This function
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* is speculative anyways, so missing one is ok.
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*/
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if (pipe->nrbufs)
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return 0;
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ret = 0;
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mutex_lock(&pipe->inode->i_mutex);
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while (!pipe->nrbufs) {
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if (signal_pending(current)) {
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ret = -ERESTARTSYS;
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break;
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}
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if (!pipe->writers)
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break;
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if (!pipe->waiting_writers) {
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if (flags & SPLICE_F_NONBLOCK) {
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ret = -EAGAIN;
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break;
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}
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}
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pipe_wait(pipe);
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}
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mutex_unlock(&pipe->inode->i_mutex);
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return ret;
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}
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/*
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* Make sure there's writeable room. Wait for room if we can, otherwise
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* return an appropriate error.
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*/
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static int link_opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
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{
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int ret;
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/*
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* Check ->nrbufs without the inode lock first. This function
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* is speculative anyways, so missing one is ok.
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*/
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if (pipe->nrbufs < PIPE_BUFFERS)
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return 0;
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ret = 0;
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mutex_lock(&pipe->inode->i_mutex);
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while (pipe->nrbufs >= PIPE_BUFFERS) {
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if (!pipe->readers) {
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send_sig(SIGPIPE, current, 0);
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ret = -EPIPE;
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break;
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}
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if (flags & SPLICE_F_NONBLOCK) {
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ret = -EAGAIN;
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break;
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}
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if (signal_pending(current)) {
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ret = -ERESTARTSYS;
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break;
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}
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pipe->waiting_writers++;
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pipe_wait(pipe);
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pipe->waiting_writers--;
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}
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mutex_unlock(&pipe->inode->i_mutex);
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return ret;
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}
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/*
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* Link contents of ipipe to opipe.
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*/
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@ -1314,9 +1393,7 @@ static int link_pipe(struct pipe_inode_info *ipipe,
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size_t len, unsigned int flags)
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{
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struct pipe_buffer *ibuf, *obuf;
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int ret, do_wakeup, i, ipipe_first;
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ret = do_wakeup = ipipe_first = 0;
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int ret = 0, i = 0, nbuf;
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/*
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* Potential ABBA deadlock, work around it by ordering lock
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@ -1324,126 +1401,62 @@ static int link_pipe(struct pipe_inode_info *ipipe,
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* could deadlock (one doing tee from A -> B, the other from B -> A).
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*/
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if (ipipe->inode < opipe->inode) {
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ipipe_first = 1;
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mutex_lock(&ipipe->inode->i_mutex);
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mutex_lock(&opipe->inode->i_mutex);
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mutex_lock_nested(&ipipe->inode->i_mutex, I_MUTEX_PARENT);
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mutex_lock_nested(&opipe->inode->i_mutex, I_MUTEX_CHILD);
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} else {
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mutex_lock(&opipe->inode->i_mutex);
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mutex_lock(&ipipe->inode->i_mutex);
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mutex_lock_nested(&opipe->inode->i_mutex, I_MUTEX_PARENT);
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mutex_lock_nested(&ipipe->inode->i_mutex, I_MUTEX_CHILD);
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}
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for (i = 0;; i++) {
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do {
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if (!opipe->readers) {
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send_sig(SIGPIPE, current, 0);
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if (!ret)
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ret = -EPIPE;
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break;
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}
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if (ipipe->nrbufs - i) {
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ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (PIPE_BUFFERS - 1));
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/*
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* If we have room, fill this buffer
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*/
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if (opipe->nrbufs < PIPE_BUFFERS) {
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int nbuf = (opipe->curbuf + opipe->nrbufs) & (PIPE_BUFFERS - 1);
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/*
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* Get a reference to this pipe buffer,
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* so we can copy the contents over.
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*/
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ibuf->ops->get(ipipe, ibuf);
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obuf = opipe->bufs + nbuf;
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*obuf = *ibuf;
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/*
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* Don't inherit the gift flag, we need to
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* prevent multiple steals of this page.
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*/
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obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
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if (obuf->len > len)
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obuf->len = len;
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opipe->nrbufs++;
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do_wakeup = 1;
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ret += obuf->len;
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len -= obuf->len;
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if (!len)
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break;
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if (opipe->nrbufs < PIPE_BUFFERS)
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continue;
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}
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/*
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* We have input available, but no output room.
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* If we already copied data, return that. If we
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* need to drop the opipe lock, it must be ordered
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* last to avoid deadlocks.
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*/
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if ((flags & SPLICE_F_NONBLOCK) || !ipipe_first) {
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if (!ret)
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ret = -EAGAIN;
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break;
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}
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if (signal_pending(current)) {
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if (!ret)
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ret = -ERESTARTSYS;
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break;
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}
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if (do_wakeup) {
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smp_mb();
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if (waitqueue_active(&opipe->wait))
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wake_up_interruptible(&opipe->wait);
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kill_fasync(&opipe->fasync_readers, SIGIO, POLL_IN);
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do_wakeup = 0;
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}
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opipe->waiting_writers++;
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pipe_wait(opipe);
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opipe->waiting_writers--;
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continue;
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}
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/*
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* No input buffers, do the usual checks for available
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* writers and blocking and wait if necessary
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* If we have iterated all input buffers or ran out of
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* output room, break.
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*/
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if (!ipipe->writers)
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if (i >= ipipe->nrbufs || opipe->nrbufs >= PIPE_BUFFERS)
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break;
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if (!ipipe->waiting_writers) {
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if (ret)
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break;
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}
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ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (PIPE_BUFFERS - 1));
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nbuf = (opipe->curbuf + opipe->nrbufs) & (PIPE_BUFFERS - 1);
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/*
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* pipe_wait() drops the ipipe mutex. To avoid deadlocks
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* with another process, we can only safely do that if
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* the ipipe lock is ordered last.
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* Get a reference to this pipe buffer,
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* so we can copy the contents over.
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*/
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if ((flags & SPLICE_F_NONBLOCK) || ipipe_first) {
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if (!ret)
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ret = -EAGAIN;
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break;
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}
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if (signal_pending(current)) {
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if (!ret)
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ret = -ERESTARTSYS;
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break;
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}
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ibuf->ops->get(ipipe, ibuf);
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if (waitqueue_active(&ipipe->wait))
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wake_up_interruptible_sync(&ipipe->wait);
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kill_fasync(&ipipe->fasync_writers, SIGIO, POLL_OUT);
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obuf = opipe->bufs + nbuf;
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*obuf = *ibuf;
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pipe_wait(ipipe);
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}
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/*
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* Don't inherit the gift flag, we need to
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* prevent multiple steals of this page.
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*/
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obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
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if (obuf->len > len)
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obuf->len = len;
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opipe->nrbufs++;
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ret += obuf->len;
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len -= obuf->len;
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i++;
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} while (len);
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mutex_unlock(&ipipe->inode->i_mutex);
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mutex_unlock(&opipe->inode->i_mutex);
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if (do_wakeup) {
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/*
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* If we put data in the output pipe, wakeup any potential readers.
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*/
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if (ret > 0) {
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smp_mb();
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if (waitqueue_active(&opipe->wait))
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wake_up_interruptible(&opipe->wait);
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@ -1464,14 +1477,29 @@ static long do_tee(struct file *in, struct file *out, size_t len,
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{
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struct pipe_inode_info *ipipe = in->f_dentry->d_inode->i_pipe;
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struct pipe_inode_info *opipe = out->f_dentry->d_inode->i_pipe;
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int ret = -EINVAL;
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/*
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* Link ipipe to the two output pipes, consuming as we go along.
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* Duplicate the contents of ipipe to opipe without actually
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* copying the data.
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*/
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if (ipipe && opipe)
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return link_pipe(ipipe, opipe, len, flags);
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if (ipipe && opipe && ipipe != opipe) {
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/*
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* Keep going, unless we encounter an error. The ipipe/opipe
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* ordering doesn't really matter.
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*/
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ret = link_ipipe_prep(ipipe, flags);
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if (!ret) {
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ret = link_opipe_prep(opipe, flags);
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if (!ret) {
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ret = link_pipe(ipipe, opipe, len, flags);
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if (!ret && (flags & SPLICE_F_NONBLOCK))
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ret = -EAGAIN;
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}
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}
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}
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return -EINVAL;
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return ret;
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}
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asmlinkage long sys_tee(int fdin, int fdout, size_t len, unsigned int flags)
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