linux-kernel - [PATCH 1/2] pipe: fix pipe buffer resizing

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Date:	Tue, 08 Jun 2010 16:28:45 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	jens.axboe@...cle.com
CC:	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] pipe: fix pipe buffer resizing

From: Miklos Szeredi <mszeredi@...e.cz>

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@...e.cz>
---
 fs/pipe.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

Index: linux.git/fs/pipe.c
===================================================================
--- linux.git.orig/fs/pipe.c	2010-06-08 15:02:16.000000000 +0200
+++ linux.git/fs/pipe.c	2010-06-08 15:50:07.000000000 +0200
@@ -1145,13 +1145,20 @@ static long pipe_set_size(struct pipe_in
 	 * 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;
--
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