diff mbox series

[FFmpeg-devel,15/21] avfilter/vf_alphamerge: Fix double-free of AVFilterFormats on error

Message ID 20200809155748.30092-9-andreas.rheinhardt@gmail.com
State Accepted
Commit fd1a2a54a478462212b25753e7106c13af1e33c6
Headers show
Series [FFmpeg-devel,1/6] avfilter/formats: Remove ff_make_formatu64_list()
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Context Check Description
andriy/default pending
andriy/make success Make finished
andriy/make_fate success Make fate finished

Commit Message

Andreas Rheinhardt Aug. 9, 2020, 3:57 p.m. UTC
The query_formats function of the alphamerge filter tries to allocate
two lists of formats which on success are attached to more permanent
objects (AVFilterLinks) for storage afterwards. If attaching a list
to an AVFilterLink succeeds, the link becomes one of the owners of
the list. Yet if attaching a list to one of its links succeeds and
an error happens lateron, both lists were manually freed, which is wrong
if the list is already owned by one or more links; these links' pointers
to their lists will become dangling and there will be a double-free/use-
after-free when these links are cleaned up automatically.

This commit fixes this by removing the custom freeing code; this will
temporarily add a leaking codepath (if attaching a list not already
owned by a link to a link fails, the list will leak), but this will
be fixed soon by making sure that an AVFilterFormats without owner will
be automatically freed when attaching it to an AVFilterLink fails.
At most one list leaks because as of this commit a new list is only
allocated after the old list has been successfully attached to a link.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
 libavfilter/vf_alphamerge.c | 26 +++++++-------------------
 1 file changed, 7 insertions(+), 19 deletions(-)
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diff --git a/libavfilter/vf_alphamerge.c b/libavfilter/vf_alphamerge.c
index 85b6d9b61a..a509f10103 100644
--- a/libavfilter/vf_alphamerge.c
+++ b/libavfilter/vf_alphamerge.c
@@ -55,27 +55,15 @@  static int query_formats(AVFilterContext *ctx)
     static const enum AVPixelFormat alpha_fmts[] = { AV_PIX_FMT_GRAY8, AV_PIX_FMT_NONE };
-    AVFilterFormats *main_formats = NULL, *alpha_formats = NULL;
+    AVFilterFormats *main_formats = ff_make_format_list(main_fmts);
     int ret;
-    if (!(main_formats = ff_make_format_list(main_fmts)) ||
-        !(alpha_formats = ff_make_format_list(alpha_fmts))) {
-            ret = AVERROR(ENOMEM);
-            goto fail;
-        }
-    if ((ret = ff_formats_ref(main_formats , &ctx->inputs[0]->out_formats)) < 0 ||
-        (ret = ff_formats_ref(alpha_formats, &ctx->inputs[1]->out_formats)) < 0 ||
-        (ret = ff_formats_ref(main_formats , &ctx->outputs[0]->in_formats)) < 0)
-            goto fail;
-    return 0;
-    if (main_formats)
-        av_freep(&main_formats->formats);
-    av_freep(&main_formats);
-    if (alpha_formats)
-        av_freep(&alpha_formats->formats);
-    av_freep(&alpha_formats);
-    return ret;
+    if ((ret = ff_formats_ref(main_formats, &ctx->inputs[0]->out_formats)) < 0 ||
+        (ret = ff_formats_ref(main_formats, &ctx->outputs[0]->in_formats)) < 0)
+            return ret;
+    return ff_formats_ref(ff_make_format_list(alpha_fmts),
+                          &ctx->inputs[1]->out_formats);
 static int config_input_main(AVFilterLink *inlink)