linux-kernel - [PATCH] jffs2: Fix race condition in jffs2_lzo

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Message-ID: <Pine.LNX.4.64.0811031714590.6298@vixen.sonytel.be>
Date:	Mon, 3 Nov 2008 17:17:49 +0100 (CET)
From:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
To:	David Woodhouse <dwmw2@...radead.org>,
	Richard Purdie <rpurdie@...nedhand.com>
cc:	linux-mtd@...ts.infradead.org,
	Linux Kernel Development <linux-kernel@...r.kernel.org>
Subject: [PATCH] jffs2: Fix race condition in jffs2_lzo_compress()

deflate_mutex protects the globals lzo_mem and lzo_compress_buf. However,
jffs2_lzo_compress() unlocks deflate_mutex _before_ it has copied out the
compressed data from lzo_compress_buf. Correct this by moving the mutex unlock
after the copy.
In addition, document what deflate_mutex actually protects.

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
---
Just noticed this when looking at the code.
The patch is untested, except for a quick compile test.

 fs/jffs2/compr_lzo.c |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

--- a/fs/jffs2/compr_lzo.c
+++ b/fs/jffs2/compr_lzo.c
@@ -19,7 +19,7 @@
 
 static void *lzo_mem;
 static void *lzo_compress_buf;
-static DEFINE_MUTEX(deflate_mutex);
+static DEFINE_MUTEX(deflate_mutex);	/* for lzo_mem and lzo_compress_buf */
 
 static void free_workspace(void)
 {
@@ -49,18 +49,21 @@ static int jffs2_lzo_compress(unsigned c
 
 	mutex_lock(&deflate_mutex);
 	ret = lzo1x_1_compress(data_in, *sourcelen, lzo_compress_buf, &compress_size, lzo_mem);
-	mutex_unlock(&deflate_mutex);
-
 	if (ret != LZO_E_OK)
-		return -1;
+		goto fail;
 
 	if (compress_size > *dstlen)
-		return -1;
+		goto fail;
 
 	memcpy(cpage_out, lzo_compress_buf, compress_size);
-	*dstlen = compress_size;
+	mutex_unlock(&deflate_mutex);
 
+	*dstlen = compress_size;
 	return 0;
+
+ fail:
+	mutex_unlock(&deflate_mutex);
+	return -1;
 }
 
 static int jffs2_lzo_decompress(unsigned char *data_in, unsigned char *cpage_out,

With kind regards,

Geert Uytterhoeven
Software Architect

Sony Techsoft Centre Europe
The Corporate Village · Da Vincilaan 7-D1 · B-1935 Zaventem · Belgium

Phone:    +32 (0)2 700 8453
Fax:      +32 (0)2 700 8622
E-mail:   Geert.Uytterhoeven@...ycom.com
Internet: http://www.sony-europe.com/

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