Re: [FFmpeg-devel] [PATCH] libavfilter: guard against ff_draw_init/ff_draw_init2 failures

[Nil Fons Miret via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

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Thanks for the clarification, attaching an updated patch. The only
change is the one comment on qrencode.c.

Thank you,
Nil

On Fri, Mar 7, 2025 at 7:28 PM Michael Niedermayer
<michael@niedermayer.cc> wrote:
>
> On Tue, Mar 04, 2025 at 10:17:25AM -0800, Nil Fons Miret via ffmpeg-devel wrote:
> > I'm not sure I understand what documentation you'd like to add. The
> > behavior of ff_draw_init* is documented in drawutils.h, would you like
> > me to add a comment where these functions are called with no risk of
> > failing (as far as I can see, only qrencode.c)? My worry is that such
> > a comment can easily become outdated. In any case, once I understand
> > your request I'm happy to add any more documentation.
>
> yes, if you add a check that is unreachable and that is intentional
> it should receive a comment.
> Otherwise it can confuse the reader, also it can be removed when someone
> realizes it is unreachable
>
> thx
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Nations do behave wisely once they have exhausted all other alternatives.
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From: Nil Fons Miret <nilf@netflix.com>
To: ffmpeg-devel@ffmpeg.org
Subject: [PATCH] libavfilter: guard against ff_draw_init/ff_draw_init2 failures
Date: Fri, 21 Feb 2025 01:18:21 +0000

The return value of ff_draw_init and ff_draw_init2 are not checked in
most usages. However, if they return an error, they don't get to the
point where they set the attributes of the FFDrawContext. These
functions are typically used in conjunction with ff_draw_color, which
checks draw->desc->flags, causing a null pointer dereference.

Signed-off-by: Nil Fons Miret <nilf@netflix.com>
---
 libavfilter/qrencode.c       | 27 ++++++++++++++++++++++-----
 libavfilter/src_avsynctest.c |  7 ++++++-
 libavfilter/vf_datascope.c   | 31 +++++++++++++++++++++++++------
 libavfilter/vf_drawtext.c    |  6 +++++-
 libavfilter/vf_pad.c         |  6 +++++-
 libavfilter/vf_shear.c       |  7 ++++++-
 libavfilter/vf_stack.c       |  6 +++++-
 libavfilter/vf_subtitles.c   | 16 +++++++++++-----
 libavfilter/vf_tile.c        |  7 ++++++-
 libavfilter/vf_tinterlace.c  |  6 +++++-
 libavfilter/vf_tpad.c        |  7 ++++++-
 libavfilter/vsrc_testsrc.c   |  9 +++++++--
 12 files changed, 109 insertions(+), 26 deletions(-)

diff --git a/libavfilter/qrencode.c b/libavfilter/qrencode.c
index f96cc8dc93..8c09b605ad 100644
--- a/libavfilter/qrencode.c
+++ b/libavfilter/qrencode.c
@@ -636,11 +636,20 @@ static int qrencodesrc_config_props(AVFilterLink *outlink)
         return AVERROR(EINVAL);
     }
 
-    ff_draw_init(&qr->draw, AV_PIX_FMT_ARGB, FF_DRAW_PROCESS_ALPHA);
+    ret = ff_draw_init(&qr->draw, AV_PIX_FMT_ARGB, FF_DRAW_PROCESS_ALPHA);
+    if (ret < 0) {
+        // This call using constants should not fail. Checking its error code for completeness.
+        av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+        return ret;
+    }
     ff_draw_color(&qr->draw, &qr->draw_foreground_color, (const uint8_t *)&qr->foreground_color);
     ff_draw_color(&qr->draw, &qr->draw_background_color, (const uint8_t *)&qr->background_color);
 
-    ff_draw_init2(&qr->draw0, outlink->format, outlink->colorspace, outlink->color_range, FF_DRAW_PROCESS_ALPHA);
+    ret = ff_draw_init2(&qr->draw0, outlink->format, outlink->colorspace, outlink->color_range, FF_DRAW_PROCESS_ALPHA);
+    if (ret < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+        return ret;
+    }
     ff_draw_color(&qr->draw0, &qr->draw0_background_color, (const uint8_t *)&qr->background_color);
 
     outlink->w = qr->rendered_padded_qrcode_width;
@@ -734,8 +743,12 @@ static int qrencode_config_input(AVFilterLink *inlink)
 
     qr->is_source = 0;
 
-    ff_draw_init2(&qr->draw, inlink->format, inlink->colorspace, inlink->color_range,
-                  FF_DRAW_PROCESS_ALPHA);
+    ret = ff_draw_init2(&qr->draw, inlink->format, inlink->colorspace, inlink->color_range,
+                        FF_DRAW_PROCESS_ALPHA);
+    if (ret < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+        return ret;
+    }
 
     V(W) = V(main_w) = inlink->w;
     V(H) = V(main_h) = inlink->h;
@@ -764,8 +777,12 @@ static int qrencode_config_input(AVFilterLink *inlink)
     PARSE_EXPR(rendered_qrcode_width);
     PARSE_EXPR(rendered_padded_qrcode_width);
 
-    ff_draw_init2(&qr->draw, inlink->format, inlink->colorspace, inlink->color_range,
+    ret = ff_draw_init2(&qr->draw, inlink->format, inlink->colorspace, inlink->color_range,
                   FF_DRAW_PROCESS_ALPHA);
+    if (ret < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+        return ret;
+    }
     ff_draw_color(&qr->draw, &qr->draw_foreground_color, (const uint8_t *)&qr->foreground_color);
     ff_draw_color(&qr->draw, &qr->draw_background_color, (const uint8_t *)&qr->background_color);
 
diff --git a/libavfilter/src_avsynctest.c b/libavfilter/src_avsynctest.c
index 6f42137f49..68dffba43a 100644
--- a/libavfilter/src_avsynctest.c
+++ b/libavfilter/src_avsynctest.c
@@ -147,6 +147,7 @@ static av_cold int config_props(AVFilterLink *outlink)
     FilterLink *l = ff_filter_link(outlink);
     AVFilterContext *ctx = outlink->src;
     AVSyncTestContext *s = ctx->priv;
+    int ret;
 
     outlink->w = s->w;
     outlink->h = s->h;
@@ -160,7 +161,11 @@ static av_cold int config_props(AVFilterLink *outlink)
     s->dir = 1;
     s->prev_intpart = INT64_MIN;
 
-    ff_draw_init2(&s->draw, outlink->format, outlink->colorspace, outlink->color_range, 0);
+    ret = ff_draw_init2(&s->draw, outlink->format, outlink->colorspace, outlink->color_range, 0);
+    if (ret < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+        return ret;
+    }
 
     ff_draw_color(&s->draw, &s->fg, s->rgba[0]);
     ff_draw_color(&s->draw, &s->bg, s->rgba[1]);
diff --git a/libavfilter/vf_datascope.c b/libavfilter/vf_datascope.c
index 75dc149fbd..6efeb875a6 100644
--- a/libavfilter/vf_datascope.c
+++ b/libavfilter/vf_datascope.c
@@ -382,11 +382,18 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
 
 static int config_input(AVFilterLink *inlink)
 {
-    DatascopeContext *s = inlink->dst->priv;
+    AVFilterContext *ctx = inlink->dst;
+    DatascopeContext *s = ctx->priv;
+
     uint8_t alpha = s->opacity * 255;
+    int ret;
 
     s->nb_planes = av_pix_fmt_count_planes(inlink->format);
-    ff_draw_init2(&s->draw, inlink->format, inlink->colorspace, inlink->color_range, 0);
+    ret = ff_draw_init2(&s->draw, inlink->format, inlink->colorspace, inlink->color_range, 0);
+    if (ret < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+        return ret;
+    }
     ff_draw_color(&s->draw, &s->white,  (uint8_t[]){ 255, 255, 255, 255} );
     ff_draw_color(&s->draw, &s->black,  (uint8_t[]){ 0, 0, 0, alpha} );
     ff_draw_color(&s->draw, &s->yellow, (uint8_t[]){ 255, 255, 0, 255} );
@@ -509,10 +516,16 @@ AVFILTER_DEFINE_CLASS(pixscope);
 
 static int pixscope_config_input(AVFilterLink *inlink)
 {
-    PixscopeContext *s = inlink->dst->priv;
+    AVFilterContext *ctx = inlink->dst;
+    PixscopeContext *s = ctx->priv;
+    int ret;
 
     s->nb_planes = av_pix_fmt_count_planes(inlink->format);
-    ff_draw_init(&s->draw, inlink->format, 0);
+    ret = ff_draw_init(&s->draw, inlink->format, 0);
+    if (ret < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+        return ret;
+    }
     ff_draw_color(&s->draw, &s->dark,  (uint8_t[]){ 0, 0, 0, s->o * 255} );
     ff_draw_color(&s->draw, &s->black, (uint8_t[]){ 0, 0, 0, 255} );
     ff_draw_color(&s->draw, &s->white, (uint8_t[]){ 255, 255, 255, 255} );
@@ -927,11 +940,17 @@ static void update_oscilloscope(AVFilterContext *ctx)
 
 static int oscilloscope_config_input(AVFilterLink *inlink)
 {
-    OscilloscopeContext *s = inlink->dst->priv;
+    AVFilterContext *ctx = inlink->dst;
+    OscilloscopeContext *s = ctx->priv;
     int size;
+    int ret;
 
     s->nb_planes = av_pix_fmt_count_planes(inlink->format);
-    ff_draw_init(&s->draw, inlink->format, 0);
+    ret = ff_draw_init(&s->draw, inlink->format, 0);
+    if (ret < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+        return ret;
+    }
     ff_draw_color(&s->draw, &s->black,   (uint8_t[]){   0,   0,   0, 255} );
     ff_draw_color(&s->draw, &s->white,   (uint8_t[]){ 255, 255, 255, 255} );
     ff_draw_color(&s->draw, &s->green,   (uint8_t[]){   0, 255,   0, 255} );
diff --git a/libavfilter/vf_drawtext.c b/libavfilter/vf_drawtext.c
index e4662f3a45..9f5d8d9998 100644
--- a/libavfilter/vf_drawtext.c
+++ b/libavfilter/vf_drawtext.c
@@ -1156,7 +1156,11 @@ static int config_input(AVFilterLink *inlink)
     char *expr;
     int ret;
 
-    ff_draw_init2(&s->dc, inlink->format, inlink->colorspace, inlink->color_range, FF_DRAW_PROCESS_ALPHA);
+    ret = ff_draw_init2(&s->dc, inlink->format, inlink->colorspace, inlink->color_range, FF_DRAW_PROCESS_ALPHA);
+    if (ret < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+        return ret;
+    }
     ff_draw_color(&s->dc, &s->fontcolor,   s->fontcolor.rgba);
     ff_draw_color(&s->dc, &s->shadowcolor, s->shadowcolor.rgba);
     ff_draw_color(&s->dc, &s->bordercolor, s->bordercolor.rgba);
diff --git a/libavfilter/vf_pad.c b/libavfilter/vf_pad.c
index 49fb272b24..0c7a1d2b44 100644
--- a/libavfilter/vf_pad.c
+++ b/libavfilter/vf_pad.c
@@ -114,7 +114,11 @@ static int config_input(AVFilterLink *inlink)
     double var_values[VARS_NB], res;
     char *expr;
 
-    ff_draw_init2(&s->draw, inlink->format, inlink->colorspace, inlink->color_range, 0);
+    ret = ff_draw_init2(&s->draw, inlink->format, inlink->colorspace, inlink->color_range, 0);
+    if (ret < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+        return ret;
+    }
     ff_draw_color(&s->draw, &s->color, s->rgba_color);
 
     var_values[VAR_IN_W]  = var_values[VAR_IW] = inlink->w;
diff --git a/libavfilter/vf_shear.c b/libavfilter/vf_shear.c
index f76ed1e4d5..2e558c0044 100644
--- a/libavfilter/vf_shear.c
+++ b/libavfilter/vf_shear.c
@@ -250,6 +250,7 @@ static int config_output(AVFilterLink *outlink)
     AVFilterContext *ctx = outlink->src;
     ShearContext *s = ctx->priv;
     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(outlink->format);
+    int ret;
 
     s->nb_planes = av_pix_fmt_count_planes(outlink->format);
     s->depth = desc->comp[0].depth;
@@ -260,7 +261,11 @@ static int config_output(AVFilterLink *outlink)
     s->planeheight[1] = s->planeheight[2] = AV_CEIL_RSHIFT(ctx->inputs[0]->h, desc->log2_chroma_h);
     s->planeheight[0] = s->planeheight[3] = ctx->inputs[0]->h;
 
-    ff_draw_init2(&s->draw, outlink->format, outlink->colorspace, outlink->color_range, 0);
+    ret = ff_draw_init2(&s->draw, outlink->format, outlink->colorspace, outlink->color_range, 0);
+    if (ret < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+        return ret;
+    }
     ff_draw_color(&s->draw, &s->color, s->fillcolor);
 
     s->filter_slice[0] = s->depth <= 8 ? filter_slice_nn8 : filter_slice_nn16;
diff --git a/libavfilter/vf_stack.c b/libavfilter/vf_stack.c
index 937b87305f..fa202ee0cc 100644
--- a/libavfilter/vf_stack.c
+++ b/libavfilter/vf_stack.c
@@ -312,7 +312,11 @@ static int config_output(AVFilterLink *outlink)
 
         if (s->fillcolor_enable) {
             const AVFilterLink *inlink = ctx->inputs[0];
-            ff_draw_init2(&s->draw, inlink->format, inlink->colorspace, inlink->color_range, 0);
+            ret = ff_draw_init2(&s->draw, inlink->format, inlink->colorspace, inlink->color_range, 0);
+            if (ret < 0) {
+                av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+                return ret;
+            }
             ff_draw_color(&s->draw, &s->color, s->fillcolor);
         }
 
diff --git a/libavfilter/vf_subtitles.c b/libavfilter/vf_subtitles.c
index 9f573ec4ed..cf23b7822a 100644
--- a/libavfilter/vf_subtitles.c
+++ b/libavfilter/vf_subtitles.c
@@ -182,12 +182,18 @@ static int query_formats(const AVFilterContext *ctx,
 
 static int config_input(AVFilterLink *inlink)
 {
-    AssContext *ass = inlink->dst->priv;
+    AVFilterContext *ctx = inlink->dst;
+    AssContext *ass = ctx->priv;
+    int ret;
 
-    ff_draw_init2(&ass->draw, inlink->format,
-                  ass_get_color_space(ass->track->YCbCrMatrix, inlink->colorspace),
-                  ass_get_color_range(ass->track->YCbCrMatrix, inlink->color_range),
-                  ass->alpha ? FF_DRAW_PROCESS_ALPHA : 0);
+    ret = ff_draw_init2(&ass->draw, inlink->format,
+                        ass_get_color_space(ass->track->YCbCrMatrix, inlink->colorspace),
+                        ass_get_color_range(ass->track->YCbCrMatrix, inlink->color_range),
+                        ass->alpha ? FF_DRAW_PROCESS_ALPHA : 0);
+    if (ret < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+        return ret;
+    }
 
     ass_set_frame_size  (ass->renderer, inlink->w, inlink->h);
     if (ass->original_w && ass->original_h) {
diff --git a/libavfilter/vf_tile.c b/libavfilter/vf_tile.c
index 9305123b33..7f2f212c4a 100644
--- a/libavfilter/vf_tile.c
+++ b/libavfilter/vf_tile.c
@@ -128,6 +128,7 @@ static int config_props(AVFilterLink *outlink)
     FilterLink *ol = ff_filter_link(outlink);
     const unsigned total_margin_w = (tile->w - 1) * tile->padding + 2*tile->margin;
     const unsigned total_margin_h = (tile->h - 1) * tile->padding + 2*tile->margin;
+    int ret;
 
     if (inlink->w > (INT_MAX - total_margin_w) / tile->w) {
         av_log(ctx, AV_LOG_ERROR, "Total width %ux%u is too much.\n",
@@ -143,7 +144,11 @@ static int config_props(AVFilterLink *outlink)
     outlink->h = tile->h * inlink->h + total_margin_h;
     outlink->sample_aspect_ratio = inlink->sample_aspect_ratio;
     ol->frame_rate = av_mul_q(il->frame_rate, av_make_q(1, tile->nb_frames - tile->overlap));
-    ff_draw_init2(&tile->draw, inlink->format, inlink->colorspace, inlink->color_range, 0);
+    ret = ff_draw_init2(&tile->draw, inlink->format, inlink->colorspace, inlink->color_range, 0);
+    if (ret < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+        return ret;
+    }
     ff_draw_color(&tile->draw, &tile->blank, tile->rgba_color);
 
     return 0;
diff --git a/libavfilter/vf_tinterlace.c b/libavfilter/vf_tinterlace.c
index de7cd88103..f013891f3e 100644
--- a/libavfilter/vf_tinterlace.c
+++ b/libavfilter/vf_tinterlace.c
@@ -228,7 +228,11 @@ static int config_out_props(AVFilterLink *outlink)
 
     if (tinterlace->mode == MODE_PAD) {
         uint8_t black[4] = { 0, 0, 0, 16 };
-        ff_draw_init2(&tinterlace->draw, outlink->format, outlink->colorspace, outlink->color_range, 0);
+        ret = ff_draw_init2(&tinterlace->draw, outlink->format, outlink->colorspace, outlink->color_range, 0);
+        if (ret < 0) {
+            av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+            return ret;
+        }
         ff_draw_color(&tinterlace->draw, &tinterlace->color, black);
         /* limited range */
         if (!ff_fmt_is_in(outlink->format, full_scale_yuvj_pix_fmts)) {
diff --git a/libavfilter/vf_tpad.c b/libavfilter/vf_tpad.c
index 7ba6fe72bf..f498bf4a3e 100644
--- a/libavfilter/vf_tpad.c
+++ b/libavfilter/vf_tpad.c
@@ -206,9 +206,14 @@ static int config_input(AVFilterLink *inlink)
     AVFilterContext *ctx = inlink->dst;
     FilterLink *l = ff_filter_link(inlink);
     TPadContext *s = ctx->priv;
+    int ret;
 
     if (needs_drawing(s)) {
-        ff_draw_init2(&s->draw, inlink->format, inlink->colorspace, inlink->color_range, 0);
+        ret = ff_draw_init2(&s->draw, inlink->format, inlink->colorspace, inlink->color_range, 0);
+        if (ret < 0) {
+            av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+            return ret;
+        }
         ff_draw_color(&s->draw, &s->color, s->rgba_color);
     }
 
diff --git a/libavfilter/vsrc_testsrc.c b/libavfilter/vsrc_testsrc.c
index 71188e624a..f3956a67b1 100644
--- a/libavfilter/vsrc_testsrc.c
+++ b/libavfilter/vsrc_testsrc.c
@@ -262,8 +262,13 @@ static int color_config_props(AVFilterLink *inlink)
     TestSourceContext *test = ctx->priv;
     int ret;
 
-    ff_draw_init2(&test->draw, inlink->format, inlink->colorspace,
-                  inlink->color_range, 0);
+    ret = ff_draw_init2(&test->draw, inlink->format, inlink->colorspace,
+                        inlink->color_range, 0);
+    if (ret < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Failed to initialize FFDrawContext\n");
+        return ret;
+    }
+
     ff_draw_color(&test->draw, &test->color, test->color_rgba);
 
     if (av_image_check_size(test->w, test->h, 0, ctx) < 0)
-- 
2.47.1


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