Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756395Ab3GVG5o (ORCPT ); Mon, 22 Jul 2013 02:57:44 -0400 Received: from hqemgate03.nvidia.com ([216.228.121.140]:16057 "EHLO hqemgate03.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932070Ab3GVG5n (ORCPT ); Mon, 22 Jul 2013 02:57:43 -0400 X-PGP-Universal: processed; by hqnvupgp07.nvidia.com on Sun, 21 Jul 2013 23:57:15 -0700 From: Alexandre Courbot To: Andrew Morton CC: , , , Alexandre Courbot Subject: [PATCH] decompressors: fix "no limit" output buffer length Date: Mon, 22 Jul 2013 15:56:09 +0900 Message-ID: <1374476169-32194-1-git-send-email-acourbot@nvidia.com> X-Mailer: git-send-email 1.8.3.2 X-NVConfidentiality: public MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2227 Lines: 57 When decompressing into memory, the output buffer length is set to some arbitrarily high value (0x7fffffff) to indicate the output is, virtually, unlimited in size. The problem with this is that some platforms have their physical memory at high physical addresses (0x80000000 or more), and that the output buffer address and its "unlimited" length cannot be added without overflowing. An example of this can be found in inflate_fast(): /* next_out is the output buffer address */ out = strm->next_out - OFF; /* avail_out is the output buffer size. end will overflow if the output * address is >= 0x80000104 */ end = out + (strm->avail_out - 257); This has huge consequences on the performance of kernel decompression, since the following exit condition of inflate_fast() will be always true: } while (in < last && out < end); Indeed, "end" has overflowed and is now always lower than "out". As a result, inflate_fast() will return after processing one single byte of input data, and will thus need to be called an unreasonably high number of times. This probably went unnoticed because kernel decompression is fast enough even with this issue. Nonetheless, adjusting the output buffer length in such a way that the above pointer arithmetic never overflows results in a kernel decompression that is about 3 times faster on affected machines. Signed-off-by: Alexandre Courbot --- lib/decompress_inflate.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/lib/decompress_inflate.c b/lib/decompress_inflate.c index 19ff89e..d619b28 100644 --- a/lib/decompress_inflate.c +++ b/lib/decompress_inflate.c @@ -48,7 +48,7 @@ STATIC int INIT gunzip(unsigned char *buf, int len, out_len = 0x8000; /* 32 K */ out_buf = malloc(out_len); } else { - out_len = 0x7fffffff; /* no limit */ + out_len = ((size_t)~0) - (size_t)out_buf; /* no limit */ } if (!out_buf) { error("Out of memory while allocating output buffer"); -- 1.8.3.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/