linux-kernel - [PATCH] lz4: add overrun checks to lz4_uncompress

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Message-ID: <20140703231103.GA4081@kroah.com>
Date:	Thu, 3 Jul 2014 16:11:03 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, Jan Beulich <JBeulich@...e.com>
Cc:	stable@...nel.org, "Don A. Bailey" <donb@...uritymouse.com>
Subject: [PATCH] lz4: add overrun checks to lz4_uncompress_unknownoutputsize()

From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

Jan points out that I forgot to make the needed fixes to the
lz4_uncompress_unknownoutputsize() function to mirror the changes done
in lz4_decompress() with regards to potential pointer overflows.

The only in-kernel user of this function is the zram code, which only
takes data from a valid compressed buffer that it made itself, so it's
not a big issue.  But due to external kernel modules using this
function, it's better to be safe here.

Reported-by: Jan Beulich <JBeulich@...e.com>
Cc: "Don A. Bailey" <donb@...uritymouse.com>
Cc: stable <stable@...r.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

diff --git a/lib/lz4/lz4_decompress.c b/lib/lz4/lz4_decompress.c
index b74da447e81e..7a85967060a5 100644
--- a/lib/lz4/lz4_decompress.c
+++ b/lib/lz4/lz4_decompress.c
@@ -192,6 +192,8 @@ static int lz4_uncompress_unknownoutputsize(const char *source, char *dest,
 			int s = 255;
 			while ((ip < iend) && (s == 255)) {
 				s = *ip++;
+				if (unlikely(length > (size_t)(length + s)))
+					goto _output_error;
 				length += s;
 			}
 		}
@@ -232,6 +234,8 @@ static int lz4_uncompress_unknownoutputsize(const char *source, char *dest,
 		if (length == ML_MASK) {
 			while (ip < iend) {
 				int s = *ip++;
+				if (unlikely(length > (size_t)(length + s)))
+					goto _output_error;
 				length += s;
 				if (s == 255)
 					continue;
@@ -284,7 +288,7 @@ static int lz4_uncompress_unknownoutputsize(const char *source, char *dest,

 	/* write overflow error detected */
 _output_error:
-	return (int) (-(((char *) ip) - source));
+	return -1;
 }

 int lz4_decompress(const unsigned char *src, size_t *src_len,
--
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