From: Al Viro viro@zeniv.linux.org.uk
commit c3497fd009ef2c59eea60d21c3ac22de3585ed7d upstream.
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: ca146f6f091e "lib/iov_iter: Fix pipe handling in _copy_to_iter_mcsafe()" Reviewed-by: Jeff Layton jlayton@kernel.org Reviewed-by: Christian Brauner (Microsoft) brauner@kernel.org Signed-off-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/pipe_fs_i.h | 9 +++++++++ lib/iov_iter.c | 15 +++++++++++---- 2 files changed, 20 insertions(+), 4 deletions(-)
--- a/include/linux/pipe_fs_i.h +++ b/include/linux/pipe_fs_i.h @@ -229,6 +229,15 @@ static inline bool pipe_buf_try_steal(st 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 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -691,6 +691,7 @@ static size_t copy_mc_pipe_to_iter(const 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)) @@ -704,11 +705,17 @@ static size_t copy_mc_pipe_to_iter(const rem = copy_mc_to_kernel(p + off, addr + xfer, chunk); chunk -= rem; kunmap_local(p); - i->head = i_head; - i->iov_offset = off + chunk; - xfer += chunk; - if (rem) + if (chunk) { + i->head = i_head; + i->iov_offset = off + chunk; + xfer += chunk; + 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++;