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fix short copy handling in copy_mc_pipe_to_iter()

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commit c3497fd009 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: ca146f6f09 "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>
This commit is contained in:
Al Viro 2022-06-12 19:50:29 -04:00 • committed by Justin Hammond
parent 0d90a0740e
commit 9ec2a5ac09
2 changed files with 20 additions and 4 deletions
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9
include/linux/pipe_fs_i.h
View file

@ -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

15
lib/iov_iter.c
View file

@ -691,6 +691,7 @@ 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))
@ -704,11 +705,17 @@ 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);
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++;