From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ffbox0-bg.mplayerhq.hu (ffbox0-bg.ffmpeg.org [79.124.17.100]) by master.gitmailbox.com (Postfix) with ESMTP id C8C4344E04 for ; Fri, 25 Nov 2022 14:11:43 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id 379DD68BC09; Fri, 25 Nov 2022 16:11:40 +0200 (EET) Received: from mail0.khirnov.net (red.khirnov.net [176.97.15.12]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id EC4D868BB6C for ; Fri, 25 Nov 2022 16:11:33 +0200 (EET) Received: from localhost (localhost [IPv6:::1]) by mail0.khirnov.net (Postfix) with ESMTP id 81BB7240499 for ; Fri, 25 Nov 2022 15:11:33 +0100 (CET) Received: from mail0.khirnov.net ([IPv6:::1]) by localhost (mail0.khirnov.net [IPv6:::1]) (amavisd-new, port 10024) with ESMTP id MZijJbq7JWkp for ; Fri, 25 Nov 2022 15:11:32 +0100 (CET) Received: from lain.khirnov.net (lain.khirnov.net [IPv6:2001:67c:1138:4306::3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256 client-signature RSA-PSS (2048 bits) client-digest SHA256) (Client CN "lain.khirnov.net", Issuer "smtp.khirnov.net SMTP CA" (verified OK)) by mail0.khirnov.net (Postfix) with ESMTPS id D277E2400F5 for ; Fri, 25 Nov 2022 15:11:32 +0100 (CET) Received: by lain.khirnov.net (Postfix, from userid 1000) id C15061601B2; Fri, 25 Nov 2022 15:11:32 +0100 (CET) From: Anton Khirnov To: FFmpeg development discussions and patches In-Reply-To: <20221125133846.GB3806951@pb2> References: <20221122225652.1341-1-michael@niedermayer.cc> <20221125133846.GB3806951@pb2> Mail-Followup-To: FFmpeg development discussions and patches Date: Fri, 25 Nov 2022 15:11:32 +0100 Message-ID: <166938549275.4503.16165224502546034668@lain.khirnov.net> User-Agent: alot/0.8.1 MIME-Version: 1.0 Subject: Re: [FFmpeg-devel] [PATCH 1/2] avcodec/pictordec: Check that the image fits in the input X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: FFmpeg development discussions and patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: FFmpeg development discussions and patches Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: Quoting Michael Niedermayer (2022-11-25 14:38:46) > t On Fri, Nov 25, 2022 at 05:45:29PM +1100, Peter Ross wrote: > > On Tue, Nov 22, 2022 at 11:56:51PM +0100, Michael Niedermayer wrote: > > > Fixes: Timeout > > > Fixes: 53438/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_PICTOR_fuzzer-5458939919859712 > > > > > > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpe > > > Signed-off-by: Michael Niedermayer > > > --- > > > libavcodec/pictordec.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/libavcodec/pictordec.c b/libavcodec/pictordec.c > > > index 71bad40a0a..09229b94fd 100644 > > > --- a/libavcodec/pictordec.c > > > +++ b/libavcodec/pictordec.c > > > @@ -162,6 +162,9 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *frame, > > > > > > if (av_image_check_size(s->width, s->height, 0, avctx) < 0) > > > return -1; > > > + if (bytestream2_get_bytes_left(&s->g) < s->width * s->height / 65536 * 5) > > > + return AVERROR_INVALIDDATA; > > > > how did you arrive at this formula? > > There are 2 coding modes, RLE and RAW > I assume usable raw images will need around W*H and thus more than RLE > RLE codes the most compressed runs by > 1 byte for val (=marker) > 1 byte run (=0) > 2 bytes run > 1 byte val > thats 5 bytes and the maximum run we can code is 65535 > > The RLE decoder loop exits before applying the last RLE run and then > there is a seperate piece of code after it that fills the last color to > the end. Iam not sure why its done like that way but if i remove that > mid exit the seperate code piece becomes unused for all images i have > so it seems all RLE images are always fully coded with no special case > at the end. > Based on this iam guesing that my formula is correct for undamaged images > but of course i could find one tomorrow that exploits the special end > handling and breaks this formula > and of course its very possible that i missed some other thing that changes > this limit This should be written in a comment above the code then, otherwise all future readers will be completely clueless. -- Anton Khirnov _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".