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[FFmpeg-devel,37/45] avcodec: Fix invalid uses of ff_codec_open2_recursive()

Message ID 20201127010249.2724610-37-andreas.rheinhardt@gmail.com
State Accepted
Commit 4e1fee405f0cbe09747f548943c083f1dc91a19e
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Series [FFmpeg-devel,01/45] avcodec/a64multienc: Fix memleak upon init failure
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Commit Message

Andreas Rheinhardt Nov. 27, 2020, 1:02 a.m. UTC
Normally no two codecs with FF_CODEC_CAP_INIT_THREADSAFE unset
can be initialized at the same time: a mutex in avcodec_open2()
ensures this. This implies that one cannot simply open a codec
with a non-threadsafe init-function from the init function of
a codec whose own init function is not threadsafe either as the child
codec couldn't acquire the lock.

ff_codec_open2_recursive() exists to get around this limitation:
If the init function of the child codec to be initialized is not
thread-safe, the mutex is unlocked, the child is initialized and
the mutex is locked again. This of course has as a prerequisite that
the parent AVCodecContext actually holds the lock, i.e. that the
parent codec's init function is not thread-safe. If it is, then one
can (and has to) just use avcodec_open2() directly (if the child's
init function is not thread-safe, then avcodec_open2() will have to
acquire the mutex itself (and potentially wait for it), so that it is
perfectly fine for an otherwise thread-safe init function to open
a codec with a potentially non-thread-safe init function via
avcodec_open2()).

Yet several of the users of ff_codec_open2_recursive() have the
FF_CODEC_CAP_INIT_THREADSAFE flag set; this only worked because
all the child codecs' init functions were thread-safe themselves
so that ff_codec_open2_recursive() didn't touch the mutex at all.
But of course the real solution to this is to directly use
avcodec_open2().

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
---
 libavcodec/avrndec.c | 2 +-
 libavcodec/imm5.c    | 4 ++--
 libavcodec/tdsc.c    | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

Comments

Anton Khirnov Dec. 4, 2020, 12:07 p.m. UTC | #1
Quoting Andreas Rheinhardt (2020-11-27 02:02:41)
> Normally no two codecs with FF_CODEC_CAP_INIT_THREADSAFE unset
> can be initialized at the same time: a mutex in avcodec_open2()
> ensures this. This implies that one cannot simply open a codec
> with a non-threadsafe init-function from the init function of
> a codec whose own init function is not threadsafe either as the child
> codec couldn't acquire the lock.
> 
> ff_codec_open2_recursive() exists to get around this limitation:
> If the init function of the child codec to be initialized is not
> thread-safe, the mutex is unlocked, the child is initialized and
> the mutex is locked again. This of course has as a prerequisite that
> the parent AVCodecContext actually holds the lock, i.e. that the
> parent codec's init function is not thread-safe. If it is, then one
> can (and has to) just use avcodec_open2() directly (if the child's
> init function is not thread-safe, then avcodec_open2() will have to
> acquire the mutex itself (and potentially wait for it), so that it is
> perfectly fine for an otherwise thread-safe init function to open
> a codec with a potentially non-thread-safe init function via
> avcodec_open2()).
> 
> Yet several of the users of ff_codec_open2_recursive() have the
> FF_CODEC_CAP_INIT_THREADSAFE flag set; this only worked because
> all the child codecs' init functions were thread-safe themselves
> so that ff_codec_open2_recursive() didn't touch the mutex at all.
> But of course the real solution to this is to directly use
> avcodec_open2().
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
> ---
>  libavcodec/avrndec.c | 2 +-
>  libavcodec/imm5.c    | 4 ++--
>  libavcodec/tdsc.c    | 2 +-
>  3 files changed, 4 insertions(+), 4 deletions(-)

ok
diff mbox series

Patch

diff --git a/libavcodec/avrndec.c b/libavcodec/avrndec.c
index c5a60acd4f..d85e3c2000 100644
--- a/libavcodec/avrndec.c
+++ b/libavcodec/avrndec.c
@@ -65,7 +65,7 @@  static av_cold int init(AVCodecContext *avctx)
         a->mjpeg_avctx->width = avctx->width;
         a->mjpeg_avctx->height = avctx->height;
 
-        if ((ret = ff_codec_open2_recursive(a->mjpeg_avctx, codec, &thread_opt)) < 0) {
+        if ((ret = avcodec_open2(a->mjpeg_avctx, codec, &thread_opt)) < 0) {
             av_log(avctx, AV_LOG_ERROR, "MJPEG codec failed to open\n");
         }
         av_dict_free(&thread_opt);
diff --git a/libavcodec/imm5.c b/libavcodec/imm5.c
index 917b414e66..5f8faa4dd0 100644
--- a/libavcodec/imm5.c
+++ b/libavcodec/imm5.c
@@ -63,7 +63,7 @@  static av_cold int imm5_init(AVCodecContext *avctx)
     ctx->h264_avctx->thread_count = 1;
     ctx->h264_avctx->flags        = avctx->flags;
     ctx->h264_avctx->flags2       = avctx->flags2;
-    ret = ff_codec_open2_recursive(ctx->h264_avctx, codec, NULL);
+    ret = avcodec_open2(ctx->h264_avctx, codec, NULL);
     if (ret < 0)
         return ret;
 
@@ -76,7 +76,7 @@  static av_cold int imm5_init(AVCodecContext *avctx)
     ctx->hevc_avctx->thread_count = 1;
     ctx->hevc_avctx->flags        = avctx->flags;
     ctx->hevc_avctx->flags2       = avctx->flags2;
-    ret = ff_codec_open2_recursive(ctx->hevc_avctx, codec, NULL);
+    ret = avcodec_open2(ctx->hevc_avctx, codec, NULL);
     if (ret < 0)
         return ret;
 
diff --git a/libavcodec/tdsc.c b/libavcodec/tdsc.c
index dfd80f6dbc..7c888b6ec8 100644
--- a/libavcodec/tdsc.c
+++ b/libavcodec/tdsc.c
@@ -125,7 +125,7 @@  static av_cold int tdsc_init(AVCodecContext *avctx)
     ctx->jpeg_avctx->flags2 = avctx->flags2;
     ctx->jpeg_avctx->dct_algo = avctx->dct_algo;
     ctx->jpeg_avctx->idct_algo = avctx->idct_algo;
-    ret = ff_codec_open2_recursive(ctx->jpeg_avctx, codec, NULL);
+    ret = avcodec_open2(ctx->jpeg_avctx, codec, NULL);
     if (ret < 0)
         return ret;