The PGX decoder accesses the lines via code like
(PIXEL*)frame->data[0] + i*frame->linesize[0]/sizeof(PIXEL)
where PIXEL is a macro parameter. This code has issues with negative
linesizes, because the type of sizeof(PIXEL) is size_t, so
that on common systems i*linesize/sizeof(PIXEL) will
always be an unsigned type that is very large in case linesize is
negative. This happens to work*, but it is undefined behaviour
and e.g. leads to "src/libavcodec/pgxdec.c:114:1: runtime error:
addition of unsigned offset to 0x7efe9c2b7040 overflowed to 0x7efe9c2b6040"
errors from UBSAN.
Fix this by using (PIXEL*)(frame->data[0] + i*frame->linesize[0]).
This is allowed because linesize has to be suitably aligned.
*: Converting a negative int to size_t works by adding SIZE_MAX + 1
to the number, so that the result is off by (SIZE_MAX + 1) /
sizeof(PIXEL). Converting the pointer arithmetic (performed on PIXELs)
back to ordinary pointers is tantamount to multiplying by sizeof(PIXEL),
so that the result is off by SIZE_MAX + 1; but SIZE_MAX + 1 == 0
for the underlying pointers.
Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@outlook.com>
---
libavcodec/pgxdec.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libavcodec/pgxdec.c b/libavcodec/pgxdec.c
index c9ada5afb5..30895b51ee 100644
--- a/libavcodec/pgxdec.c
+++ b/libavcodec/pgxdec.c
@@ -97,7 +97,7 @@ error:
{
\
int i, j;
\
for (i = 0; i < height; i++) {
\
- PIXEL *line = (PIXEL*)frame->data[0] +
i*frame->linesize[0]/sizeof(PIXEL); \
+ PIXEL *line = (PIXEL*)(frame->data[0] + i * frame->linesize[0]);
\
for (j = 0; j < width; j++) {
\
unsigned val;
\
if (sign)
\
--
2.32.0
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