pipe: fix pipe buffer resizing

pipe_set_size() needs to copy pipe bufs from the old circular buffer
to the new.

The current code gets this wrong in multiple ways, resulting in oops.

Test program is available here:
  http://www.kernel.org/pub/linux/kernel/people/mszeredi/piperesize/

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/fs/pipe.c b/fs/pipe.c
index 69c4c7c13ea9..f31e2d472984 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1145,13 +1145,20 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long nr_pages)
          * and adjust the indexes.
          */
         if (pipe->nrbufs) {
-                const unsigned int tail = pipe->nrbufs & (pipe->buffers - 1);
-                const unsigned int head = pipe->nrbufs - tail;
+                unsigned int tail;
+                unsigned int head;
 
+                tail = pipe->curbuf + pipe->nrbufs;
+                if (tail < pipe->buffers)
+                        tail = 0;
+                else
+                        tail &= (pipe->buffers - 1);
+
+                head = pipe->nrbufs - tail;
                 if (head)
                         memcpy(bufs, pipe->bufs + pipe->curbuf, head * sizeof(struct pipe_buffer));
                 if (tail)
-                        memcpy(bufs + head, pipe->bufs + pipe->curbuf, tail * sizeof(struct pipe_buffer));
+                        memcpy(bufs + head, pipe->bufs, tail * sizeof(struct pipe_buffer));
         }
 
         pipe->curbuf = 0;