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splice: only read in as much information as there is pipe buffer space

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Andreas Grünbacher reports that on the two filesystems that support
iomap directio, it's possible for splice() to return -EAGAIN (instead of
a short splice) if the pipe being written to has less space available in
its pipe buffers than the length supplied by the calling process.

Months ago we fixed splice_direct_to_actor to clamp the length of the
read request to the size of the splice pipe.  Do the same to do_splice.

Fixes: 1761444557 ("splice: don't read more than available pipe space")
Reported-by: syzbot+3c01db6025f26530cf8d@syzkaller.appspotmail.com
Reported-by: Andreas Grünbacher <andreas.gruenbacher@gmail.com>
Reviewed-by: Andreas Grünbacher <andreas.gruenbacher@gmail.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Darrick J. Wong 2019-10-15 08:44:32 -07:00
parent 4f5cafb5cb
commit 3253d9d093
1 changed files with 11 additions and 3 deletions
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14
fs/splice.c
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@ -945,12 +945,13 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
WARN_ON_ONCE(pipe->nrbufs != 0);
while (len) {
unsigned int pipe_pages;
size_t read_len;
loff_t pos = sd->pos, prev_pos = pos;
/* Don't try to read more the pipe has space for. */
read_len = min_t(size_t, len,
(pipe->buffers - pipe->nrbufs) << PAGE_SHIFT);
pipe_pages = pipe->buffers - pipe->nrbufs;
read_len = min(len, (size_t)pipe_pages << PAGE_SHIFT);
ret = do_splice_to(in, &pos, pipe, read_len, flags);
if (unlikely(ret <= 0))
goto out_release;
@ -1180,8 +1181,15 @@ static long do_splice(struct file *in, loff_t __user *off_in,
pipe_lock(opipe);
ret = wait_for_space(opipe, flags);
if (!ret)
if (!ret) {
unsigned int pipe_pages;
/* Don't try to read more the pipe has space for. */
pipe_pages = opipe->buffers - opipe->nrbufs;
len = min(len, (size_t)pipe_pages << PAGE_SHIFT);
ret = do_splice_to(in, &offset, opipe, len, flags);
}
pipe_unlock(opipe);
if (ret > 0)
wakeup_pipe_readers(opipe);