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From 95ea5226c870449522240ccff26f0b006037c520 Mon Sep 17 00:00:00 2001
From: Vincent Rabaud <vrabaud@google.com>
Date: Mon, 11 Sep 2023 16:06:08 +0200
Subject: [PATCH 2/2] Fix invalid incremental decoding check.
The first condition is only necessary if we have not read enough
(enough being defined by src_last, not src_end which is the end
of the image).
The second condition now fits the comment below: "if not
incremental, and we are past the end of buffer".
BUG=oss-fuzz:62136
Change-Id: I0700f67c62db8e1c02c2e429a069a71e606a5e4f
CVE: CVE-2023-4863
Upstream-Status: Backport [https://github.com/webmproject/libwebp/commit/95ea5226c870449522240ccff26f0b006037c520]
Signed-off-by: Soumya Sambu <soumya.sambu@windriver.com>
---
src/dec/vp8l_dec.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/src/dec/vp8l_dec.c b/src/dec/vp8l_dec.c
index 186b0b2..59a9e64 100644
--- a/src/dec/vp8l_dec.c
+++ b/src/dec/vp8l_dec.c
@@ -1241,9 +1241,20 @@ static int DecodeImageData(VP8LDecoder* const dec, uint32_t* const data,
}
br->eos_ = VP8LIsEndOfStream(br);
- if (dec->incremental_ && br->eos_ && src < src_end) {
+ // In incremental decoding:
+ // br->eos_ && src < src_last: if 'br' reached the end of the buffer and
+ // 'src_last' has not been reached yet, there is not enough data. 'dec' has to
+ // be reset until there is more data.
+ // !br->eos_ && src < src_last: this cannot happen as either the buffer is
+ // fully read, either enough has been read to reach 'src_last'.
+ // src >= src_last: 'src_last' is reached, all is fine. 'src' can actually go
+ // beyond 'src_last' in case the image is cropped and an LZ77 goes further.
+ // The buffer might have been enough or there is some left. 'br->eos_' does
+ // not matter.
+ assert(!dec->incremental_ || (br->eos_ && src < src_last) || src >= src_last);
+ if (dec->incremental_ && br->eos_ && src < src_last) {
RestoreState(dec);
- } else if (!br->eos_) {
+ } else if ((dec->incremental_ && src >= src_last) || !br->eos_) {
// Process the remaining rows corresponding to last row-block.
if (process_func != NULL) {
process_func(dec, row > last_row ? last_row : row);
--
2.40.0
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