On 5/4/2021 5:13 PM, Andreas Rheinhardt wrote:
James Almer:
Signed-off-by: James Almer <jamr...@gmail.com>
---
libavutil/imgutils.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libavutil/imgutils.c b/libavutil/imgutils.c
index 53faad889a..aaee0dfb7a 100644
--- a/libavutil/imgutils.c
+++ b/libavutil/imgutils.c
@@ -166,7 +166,7 @@ int av_image_fill_pointers(uint8_t *data[4], enum
AVPixelFormat pix_fmt, int hei
}
data[0] = ptr;
- for (i = 1; i < 4 && sizes[i]; i++)
+ for (i = 1; i < 4 && data[i - 1] && sizes[i]; i++)
data[i] = data[i - 1] + sizes[i - 1];
return ret;
I see two ways to make this a NULL + offset: First, if ptr == NULL; and
second if data[i - 1] + sizes[i - 1] no longer fits into the allocated
buffer and happens to yield NULL (very unlikely, but possible) in which
case data[i] + sizes[i] would be NULL + offset. In the second case, the
first addition is already undefined behaviour against which we cannot
guard at all: We don't know the size of the buffer. The only thing we
can guard against is ptr being NULL; we can even error out in this
scenario, but I don't know how disruptive that would be.
That'd be an undesirable breakage, yes. Aside from filling data[], the
function also returns the size of the buffer that should be allocated,
so that functionality should remain even when ptr == NULL.
Notice that in C the result of pointer + offset can never be NULL, so a
compiler could optimize the check for data[i - 1] to just a check for ptr.
If you say there's no warranty that an scenario where data[i-1] +
size[i-1] == NULL will break the for loop in the next iteration, and no
way to guard against it at all, then we can just return right before
attempting to set data[] when ptr == NULL, and at least simplify that
scenario.
- Andreas
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