[FFmpeg-devel] [PR] avformat/img2dec: reject input images too big to fit into a single packet (PR #21334)

[Timo Rothenpieler via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #21334 opened by Timo Rothenpieler (BtbN)
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21334
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21334.patch

Not entirely sure if it should instead use some entirely different
approach here, given that images exceeding 2GB don't seem that crazy
to me, but so far processing such images results in a heap overflow,
since the size addition overflows and a much too small packet is
allocated and its size never checked again when writing into it.

Fixes #YWH-PGM40646-32


>From adebaa447e94078d17e44cefe3ade507d6c5b0f2 Mon Sep 17 00:00:00 2001
From: Timo Rothenpieler <timo@rothenpieler.org>
Date: Wed, 31 Dec 2025 03:41:21 +0100
Subject: [PATCH] avformat/img2dec: reject input images too big to fit into a
 single packet

Not entirely sure if it should instead use some entirely different
approach here, given that images exceeding 2GB don't seem that crazy
to me, but so far processing such images results in a heap overflow,
since the size addition overflows and a much too small packet is
allocated and its size never checked again when writing into it.

Fixes #YWH-PGM40646-32
---
 libavformat/img2dec.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/libavformat/img2dec.c b/libavformat/img2dec.c
index 8f1c9013ca..9c2c519e4f 100644
--- a/libavformat/img2dec.c
+++ b/libavformat/img2dec.c
@@ -365,8 +365,10 @@ int ff_img_read_packet(AVFormatContext *s1, AVPacket *pkt)
     VideoDemuxData *s = s1->priv_data;
     AVBPrint filename;
     int i, res;
-    int size[3]           = { 0 }, ret[3] = { 0 };
-    AVIOContext *f[3]     = { NULL };
+    int ret[3] = { 0 };
+    int64_t size[3] = { 0 };
+    int64_t total_size;
+    AVIOContext *f[3] = { NULL };
     AVCodecParameters *par = s1->streams[0]->codecpar;
 
     av_bprint_init(&filename, 0, AV_BPRINT_SIZE_UNLIMITED);
@@ -456,7 +458,11 @@ int ff_img_read_packet(AVFormatContext *s1, AVPacket *pkt)
         }
     }
 
-    res = av_new_packet(pkt, size[0] + size[1] + size[2]);
+    total_size = size[0] + size[1] + size[2];
+    if (total_size < 0 || total_size > INT_MAX || size[0] > INT_MAX || size[1] > INT_MAX || size[2] > INT_MAX)
+        return AVERROR_INVALIDDATA;
+
+    res = av_new_packet(pkt, total_size);
     if (res < 0) {
         goto fail;
     }
-- 
2.49.1

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