Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755959Ab0DCUlX (ORCPT ); Sat, 3 Apr 2010 16:41:23 -0400 Received: from filtteri6.pp.htv.fi ([213.243.153.189]:34108 "EHLO filtteri6.pp.htv.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755585Ab0DCUlQ (ORCPT ); Sat, 3 Apr 2010 16:41:16 -0400 Date: Sat, 3 Apr 2010 23:41:18 +0300 (EEST) From: Aaro Koskinen X-X-Sender: aaro@loser To: Andrew Morton cc: Aaro Koskinen , linux-kernel@vger.kernel.org, hsweeten@visionengravers.com, hpa@zytor.com, eric.piel@tremplin-utc.net, stable Subject: Re: [PATCH] initramfs: prevent buffer overflow when unpacking to rootfs In-Reply-To: <20100402145702.fb9ccfdc.akpm@linux-foundation.org> Message-ID: References: <1270115146-25342-1-git-send-email-aaro.koskinen@iki.fi> <20100402145702.fb9ccfdc.akpm@linux-foundation.org> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1912 Lines: 54 On Fri, 2 Apr 2010, Andrew Morton wrote: > On Thu, 1 Apr 2010 12:45:46 +0300 > Aaro Koskinen wrote: > >> Garbage in the initrd memory area may result in the unpack routine >> accessing memory outside the buffer. The patch adds a check that the >> specified area size is not exceeded. >> >> Signed-off-by: Aaro Koskinen >> Cc: stable >> --- >> >> The patch prevents the following kernel panic on Amstrad E3: >> >> Unpacking initramfs... >> Unable to handle kernel paging request at virtual address c20121a7 >> >> ... >> >> --- a/init/initramfs.c >> +++ b/init/initramfs.c >> @@ -460,6 +460,8 @@ static char * __init unpack_to_rootfs(char *buf, unsigned len) >> } >> if (state != Reset) >> error("junk in compressed archive"); >> + if (my_inptr >= len) >> + break; >> this_header = saved_offset + my_inptr; >> buf += my_inptr; >> len -= my_inptr; > > OK, so if I'm understanding this right, the call to > > decompress(buf, len, NULL, flush_buffer, NULL, &my_inptr, error); > > has gone and generated more output data than it was asked to generate? > > If so, isn't that a bug in the decompressor? Which one is your system using? The decompressor is gzip, and it returned correct buffer position. The problem was that the loop in unpack_to_rootfs() continued to process the remaining buffer. my_inptr was never again updated (decompress_method() did not recognize the remaining garbage data, so there was no further calls to decompressor). The loop kept subtracting my_inptr from len eventually exceeding it. Perhaps there should be some better logic to give up earlier. A. -- 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/