[FFmpeg-devel] [PATCH] avutil/hwcontext_vulkan: don't over-map buffers with prior padding

[FFmpeg-devel] [PATCH] avutil/hwcontext_vulkan: don't over-map buffers with prior padding

[Niklas Haas]

From: Niklas Haas <git@haasn.dev>

If the image data is not at the start of the buffer allocation, such as
when the buffer has padding before the image data, this function maps too
much memory, since src_data + src_buf->size exceeds the buffer size.

Fix this by subtracting the difference between the buffer start and the
provided image data pointer from the size of the memory range to map.

An easy way to reproduce this issue is using the vf_pad filter, which
allocates image data buffers with a nonzero offset whenever padding is
requested before the start of the image data.
---
 libavutil/vulkan.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libavutil/vulkan.c b/libavutil/vulkan.c
index f36f2bb7cf..04cc45ee05 100644
--- a/libavutil/vulkan.c
+++ b/libavutil/vulkan.c
@@ -1408,7 +1408,8 @@ int ff_vk_host_map_buffer(FFVulkanContext *s, AVBufferRef **dst,
         return AVERROR(ENOMEM);
 
     /* Add the offset at the start, which gets ignored */
-    buffer_size = offs + src_buf->size;
+    const ptrdiff_t src_offset = src_data - src_buf->data;
+    buffer_size = offs + (src_buf->size - src_offset);
     buffer_size = FFALIGN(buffer_size, s->props.properties.limits.minMemoryMapAlignment);
     buffer_size = FFALIGN(buffer_size, s->hprops.minImportedHostPointerAlignment);
 
-- 
2.49.0

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Re: [FFmpeg-devel] [PATCH] avutil/hwcontext_vulkan: don't over-map buffers with prior padding

[Lynne]

On 15/07/2025 19:51, Niklas Haas wrote:
> From: Niklas Haas <git@haasn.dev>
> 
> If the image data is not at the start of the buffer allocation, such as
> when the buffer has padding before the image data, this function maps too
> much memory, since src_data + src_buf->size exceeds the buffer size.
> 
> Fix this by subtracting the difference between the buffer start and the
> provided image data pointer from the size of the memory range to map.
> 
> An easy way to reproduce this issue is using the vf_pad filter, which
> allocates image data buffers with a nonzero offset whenever padding is
> requested before the start of the image data.
> ---
>   libavutil/vulkan.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/libavutil/vulkan.c b/libavutil/vulkan.c
> index f36f2bb7cf..04cc45ee05 100644
> --- a/libavutil/vulkan.c
> +++ b/libavutil/vulkan.c
> @@ -1408,7 +1408,8 @@ int ff_vk_host_map_buffer(FFVulkanContext *s, AVBufferRef **dst,
>           return AVERROR(ENOMEM);
>   
>       /* Add the offset at the start, which gets ignored */
> -    buffer_size = offs + src_buf->size;
> +    const ptrdiff_t src_offset = src_data - src_buf->data;
> +    buffer_size = offs + (src_buf->size - src_offset);
>       buffer_size = FFALIGN(buffer_size, s->props.properties.limits.minMemoryMapAlignment);
>       buffer_size = FFALIGN(buffer_size, s->hprops.minImportedHostPointerAlignment);
>   

lgtm
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