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Date: Fri, 12 Aug 2016 10:10:10 +0000
From: 连一汉 <lianyihan@....cn>
To: "oss-security@...ts.openwall.com" <oss-security@...ts.openwall.com>
Subject: [CVE-2016-6671] ffmpeg buffer overflow when decoding swf
Hi , I’m Lian ,a security researcher in Qihoo 360.
I found a vulnerability of ffmpeg .
This is a buffer overflow vulnerability when decoding swf, and has been assigned the CVE identifier CVE-2016-6671 .
Version Affected: <=3.1.1
Fixed Version: 3.1.2
Web site: http://ffmpeg.org/security.html
Vulnerability detail:
================== test command =======================
Ffmpeg -i poc.swf -b:v 640k -y output.ts
============== affected code and crash info =================
On libavcodec/rawdec.c :
raw_decode()
{
…
memcpy(context->palette->data, pal, avpkt->size - vid_size); // buffer overflow
…
}
Back trace:
#0 0x00007f6a128955f7 in raise () from /lib64/libc.so.6
#1 0x00007f6a12896ce8 in abort () from /lib64/libc.so.6
#2 0x00000000004d0d86 in __sanitizer::Abort() ()
at /tmp/llvm-3.8.0rc3.src/utils/release/final/llvm.src/projects/compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cc:124
#3 0x00000000004beb65 in __sanitizer::Die() ()
at /tmp/llvm-3.8.0rc3.src/utils/release/final/llvm.src/projects/compiler-rt/lib/sanitizer_common/sanitizer_common.cc:147
#4 0x00000000004b8a22 in ~ScopedInErrorReport () at /tmp/llvm-3.8.0rc3.src/utils/release/final/llvm.src/projects/compiler-rt/lib/asan/asan_report.cc:709
#5 0x00000000004b83d1 in ReportGenericError () at /tmp/llvm-3.8.0rc3.src/utils/release/final/llvm.src/projects/compiler-rt/lib/asan/asan_report.cc:1111
#6 0x000000000049c0e2 in __interceptor_memcpy ()
at /tmp/llvm-3.8.0rc3.src/utils/release/final/llvm.src/projects/compiler-rt/lib/asan/asan_interceptors.cc:438
#7 0x0000000001444fdb in raw_decode (avctx=0x619000008c80, data=0x61500003c580, got_frame=0x7fff89caa048, avpkt=0x7fff89ca9a18)
at libavcodec/rawdec.c:381
#8 0x00000000015e7f18 in avcodec_decode_video2 (avctx=0x619000008c80, picture=0x61500003c580, got_picture_ptr=0x7fff89caa048, avpkt=0x7fff89ca9ff0)
at libavcodec/utils.c:2224
#9 0x00000000005285ee in decode_video (ist=0x61400001ba40, pkt=0x7fff89ca9ff0, got_output=0x7fff89caa048) at ffmpeg.c:2087
#10 0x000000000051733a in process_input_packet (ist=0x61400001ba40, pkt=0x7fff89caa888, no_eof=0) at ffmpeg.c:2340
#11 0x000000000051ec93 in process_input (file_index=0) at ffmpeg.c:4020
#12 0x0000000000514763 in transcode_step () at ffmpeg.c:4108
#13 0x000000000050d3f1 in transcode () at ffmpeg.c:4162
#14 0x000000000050c2e9 in main (argc=6, argv=0x7fff89caad18) at ffmpeg.c:4355
====================== patch ===========================
Found-by: <lianyihan@....cn>
Signed-off-by: Michael Niedermayer <michael@...dermayer.cc>
---
libavcodec/rawdec.c | 25 +++++++++++++++++--------
1 file changed, 17 insertions(+), 8 deletions(-)
diff --git a/libavcodec/rawdec.c b/libavcodec/rawdec.c
index 765e567..f97a839 100644
--- a/libavcodec/rawdec.c
+++ b/libavcodec/rawdec.c
@@ -365,20 +365,29 @@ static int raw_decode(AVCodecContext *avctx, void *da=
ta, int *got_frame,
if (avctx->pix_fmt =3D=3D AV_PIX_FMT_PAL8) {
const uint8_t *pal =3D av_packet_get_side_data(avpkt, AV_PKT_DATA_=
PALETTE,
NULL);
- if (pal) {
- av_buffer_unref(&context->palette);
+ int ret;
+ if (!context->palette)
context->palette =3D av_buffer_alloc(AVPALETTE_SIZE);
- if (!context->palette) {
- av_buffer_unref(&frame->buf[0]);
- return AVERROR(ENOMEM);
- }
+ if (!context->palette) {
+ av_buffer_unref(&frame->buf[0]);
+ return AVERROR(ENOMEM);
+ }
+ ret =3D av_buffer_make_writable(&context->palette);
+ if (ret < 0) {
+ av_buffer_unref(&frame->buf[0]);
+ return ret;
+ }
+
+ if (pal) {
memcpy(context->palette->data, pal, AVPALETTE_SIZE);
frame->palette_has_changed =3D 1;
} else if (context->is_nut_pal8) {
int vid_size =3D avctx->width * avctx->height;
- if (avpkt->size - vid_size) {
+ int pal_size =3D avpkt->size - vid_size;
+
+ if (avpkt->size > vid_size && pal_size <=3D AVPALETTE_SIZE) {
pal =3D avpkt->data + vid_size;
- memcpy(context->palette->data, pal, avpkt->size - vid_size=
);
+ memcpy(context->palette->data, pal, pal_size);
frame->palette_has_changed =3D 1;
}
}
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