[PR] avfilter/aarch64/vf_bwdif_init: Fix stride bound check (PR #24205)

PR #24205 opened by haochenc
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/24205
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/24205.patch

Fix stride condition when bounding w.

Signed-off-by: Hao Chen <[email protected]>

# Summary of changes

This PR fixes a bounds-checking bug in the AArch64 NEON implementation of `vf_bwdif_init_aarch64.c`.

The underlying assembly function operates on 16-byte chunks. The code previously attempted to take a shortcut: if the image width `w` is not a multiple of 16, but both the destination and source strides have enough padding to contain the rounded-up width (`FFALIGN(w, 16)`), it allows the assembly code to safely overwrite the padding bytes. This avoids the overhead of dropping into a slow C fallback for the tail pixels.

However, the logic erroneously checked if the strides were *less than or equal to* the padded width (`d_stride <= w1  && s_stride <= w1`), rather than *greater than or equal to* (`>=`). This could lead to out-of-bounds writes and memory corruption by incorrectly taking the shortcut when padding bytes are not actually available, causing the assembly loop to trample over the adjacent scanline's data. This commit fixes the condition to correctly ensure `d_stride >= w1 && s_stride >= w1`.

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>From 8dd232a1b949ac98c6e94d119bc17df0a7292c23 Mon Sep 17 00:00:00 2001
From: Hao Chen <[email protected]>
Date: Fri, 14 Aug 2026 19:42:47 +0000
Subject: [PATCH] avfilter/aarch64/vf_bwdif_init: Fix stride bound check

Fix stride condition when bounding w.

Signed-off-by: Hao Chen <[email protected]>
---
 libavfilter/aarch64/vf_bwdif_init_aarch64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavfilter/aarch64/vf_bwdif_init_aarch64.c b/libavfilter/aarch64/vf_bwdif_init_aarch64.c
index efcb31efff..9b83865bdb 100644
--- a/libavfilter/aarch64/vf_bwdif_init_aarch64.c
+++ b/libavfilter/aarch64/vf_bwdif_init_aarch64.c
@@ -52,7 +52,7 @@ static void filter_line3_helper(void * dst1, int d_stride,
     // having to invoke the C version to clean up the tail.
     const int w1 = FFALIGN(w, 16);
     const int w0 = clip_max != 255 ? 0 :
-                   d_stride <= w1 && s_stride <= w1 ? w : w & ~15;
+                   d_stride >= w1 && s_stride >= w1 ? w : w & ~15;
 
     ff_bwdif_filter_line3_neon(dst1, d_stride,
                                prev1, cur1, next1, s_stride,
-- 
2.52.0

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