Commit c3497fd0 authored by Al Viro's avatar Al Viro
Browse files

fix short copy handling in copy_mc_pipe_to_iter() 



Unlike other copying operations on ITER_PIPE, copy_mc_to_iter() can
result in a short copy.  In that case we need to trim the unused
buffers, as well as the length of partially filled one - it's not
enough to set ->head, ->iov_offset and ->count to reflect how
much had we copied.  Not hard to fix, fortunately...

I'd put a helper (pipe_discard_from(pipe, head)) into pipe_fs_i.h,
rather than iov_iter.c - it has nothing to do with iov_iter and
having it will allow us to avoid an ugly kludge in fs/splice.c.
We could put it into lib/iov_iter.c for now and move it later,
but I don't see the point going that way...

Cc: stable@kernel.org # 4.19+
Fixes: ca146f6f "lib/iov_iter: Fix pipe handling in _copy_to_iter_mcsafe()"
Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
Reviewed-by: default avatarChristian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent b13baccc

include/linux/pipe_fs_i.h

+9 −0
Original line number Diff line number Diff line
@@ -229,6 +229,15 @@ static inline bool pipe_buf_try_steal(struct pipe_inode_info *pipe, 
	return buf->ops->try_steal(pipe, buf);

}



static inline void pipe_discard_from(struct pipe_inode_info *pipe,

		unsigned int old_head)

{

	unsigned int mask = pipe->ring_size - 1;



	while (pipe->head > old_head)

		pipe_buf_release(pipe, &pipe->bufs[--pipe->head & mask]);

}



/* Differs from PIPE_BUF in that PIPE_SIZE is the length of the actual

   memory allocation, whereas PIPE_BUF makes atomicity guarantees.  */

#define PIPE_SIZE		PAGE_SIZE

lib/iov_iter.c

+11 −4
Original line number Diff line number Diff line
@@ -689,6 +689,7 @@ static size_t copy_mc_pipe_to_iter(const void *addr, size_t bytes, 
	struct pipe_inode_info *pipe = i->pipe;

	unsigned int p_mask = pipe->ring_size - 1;

	unsigned int i_head;

	unsigned int valid = pipe->head;

	size_t n, off, xfer = 0;



	if (!sanity(i))
@@ -702,11 +703,17 @@ static size_t copy_mc_pipe_to_iter(const void *addr, size_t bytes, 
		rem = copy_mc_to_kernel(p + off, addr + xfer, chunk);

		chunk -= rem;

		kunmap_local(p);

		if (chunk) {

			i->head = i_head;

			i->iov_offset = off + chunk;

			xfer += chunk;

		if (rem)

			valid = i_head + 1;

		}

		if (rem) {

			pipe->bufs[i_head & p_mask].len -= rem;

			pipe_discard_from(pipe, valid);

			break;

		}

		n -= chunk;

		off = 0;

		i_head++;