[FFmpeg-devel] [PATCH] avcodec/webp: fix incorrectly returning AVERROR_INVALIDDATA when building Huffman reader (PR #20316)

[rzumer via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #20316 opened by rzumer
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20316
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20316.patch

This corrects an error in commit c33f16d, causing the single-symbol special case to fall through to the no-symbol one and returning AVERROR_INVALIDDATA instead of a success status code. Since the same commit removes shared logic between the two special cases, I split them up to simplify it as a follow-up.


From c031ae60335ed0f02b5b8c80a069656b68f66b68 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rapha=C3=ABl=20Zumer?= <rzumer@tebako.net>
Date: Fri, 22 Aug 2025 12:44:09 -0400
Subject: [PATCH 1/2] avcodec/webp: fix incorrectly returning
 AVERROR_INVALIDDATA when building Huffman reader
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

This corrects an error in commit c33f16d.

Signed-off-by: Raphaël Zumer <rzumer@tebako.net>
---
 libavcodec/webp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/libavcodec/webp.c b/libavcodec/webp.c
index 56c3ec6d28..a350dff7a7 100644
--- a/libavcodec/webp.c
+++ b/libavcodec/webp.c
@@ -281,6 +281,7 @@ static int huff_reader_build_canonical(HuffReader *r, const uint8_t *code_length
             r->nb_symbols = 1;
             r->simple = 1;
             r->simple_symbols[0] = syms[0];
+            return 0;
         }
         // No symbols
         return AVERROR_INVALIDDATA;
-- 
2.49.1


From 037814053f5cc47f07401bc6764bdc15d92fd70c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rapha=C3=ABl=20Zumer?= <rzumer@tebako.net>
Date: Fri, 22 Aug 2025 13:32:48 -0400
Subject: [PATCH 2/2] avcodec/webp: simplify special-case handling when
 building Huffman reader
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Signed-off-by: Raphaël Zumer <rzumer@tebako.net>
---
 libavcodec/webp.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/libavcodec/webp.c b/libavcodec/webp.c
index a350dff7a7..c1c35fded0 100644
--- a/libavcodec/webp.c
+++ b/libavcodec/webp.c
@@ -275,17 +275,19 @@ static int huff_reader_build_canonical(HuffReader *r, const uint8_t *code_length
             lens[idx] = code_lengths[sym];
         }
     }
-    if (nb_codes <= 1) {
-        if (nb_codes == 1) {
-            /* special-case 1 symbol since the vlc reader cannot handle it */
-            r->nb_symbols = 1;
-            r->simple = 1;
-            r->simple_symbols[0] = syms[0];
-            return 0;
-        }
+
+    if (nb_codes == 0) {
         // No symbols
         return AVERROR_INVALIDDATA;
     }
+    if (nb_codes == 1) {
+        // Special-case 1 symbol since the VLC reader cannot handle it
+        r->nb_symbols = 1;
+        r->simple = 1;
+        r->simple_symbols[0] = syms[0];
+        return 0;
+    }
+
     ret = ff_vlc_init_from_lengths(&r->vlc, 8, nb_codes, lens, 1,
                                    syms, 2, 2, 0, VLC_INIT_OUTPUT_LE, logctx);
     if (ret < 0)
-- 
2.49.1

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