h264: fix deadlocks on incomplete reference frame decoding.

If decoding a second complementary field, and the first was
decoded in our thread, mark decoding of that field as complete.
If decoding fails, mark the decoded field/frame as complete.
Do not allow switching between field modes or field/frame mode
between slices within the same field/frame. Ensure that two
subsequent fields cover top/bottom (rather than top/frame,
bottom/frame or such nonsense situations).

Fixes various deadlocks when decoding samples with errors in
reference frames.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org

libavcodec/h264.c

@@ -2747,8 +2747,7 @@ static int field_end(H264Context *h, int in_setup)
     s->mb_y = 0;
 
     if (!in_setup && !s->dropable)
-        ff_thread_report_progress(&s->current_picture_ptr->f,
+        ff_thread_report_progress(&s->current_picture_ptr->f, INT_MAX,
-                                  (16 * s->mb_height >> FIELD_PICTURE) - 1,
                                   s->picture_structure == PICT_BOTTOM_FIELD);
 
     if (CONFIG_H264_VDPAU_DECODER &&
@@ -2871,9 +2870,7 @@ static int decode_slice_header(H264Context *h, H264Context *h0)
     int num_ref_idx_active_override_flag;
     unsigned int slice_type, tmp, i, j;
     int default_ref_list_done = 0;
-    int last_pic_structure;
+    int last_pic_structure, last_pic_dropable;
-
-    s->dropable = h->nal_ref_idc == 0;
 
     /* FIXME: 2tap qpel isn't implemented for high bit depth. */
     if ((s->avctx->flags2 & CODEC_FLAG2_FAST) &&
@@ -2893,8 +2890,14 @@ static int decode_slice_header(H264Context *h, H264Context *h0)
         }
 
         h0->current_slice = 0;
-        if (!s0->first_field)
+        if (!s0->first_field) {
+            if (s->current_picture_ptr && !s->dropable &&
+                s->current_picture_ptr->owner2 == s) {
+                ff_thread_report_progress(&s->current_picture_ptr->f, INT_MAX,
+                                          s->picture_structure == PICT_BOTTOM_FIELD);
+            }
             s->current_picture_ptr = NULL;
+        }
     }
 
     slice_type = get_ue_golomb_31(&s->gb);
@@ -3103,6 +3106,8 @@ static int decode_slice_header(H264Context *h, H264Context *h0)
     h->mb_mbaff        = 0;
     h->mb_aff_frame    = 0;
     last_pic_structure = s0->picture_structure;
+    last_pic_dropable  = s->dropable;
+    s->dropable        = h->nal_ref_idc == 0;
     if (h->sps.frame_mbs_only_flag) {
         s->picture_structure = PICT_FRAME;
     } else {
@@ -3115,7 +3120,17 @@ static int decode_slice_header(H264Context *h, H264Context *h0)
     }
     h->mb_field_decoding_flag = s->picture_structure != PICT_FRAME;
 
-    if (h0->current_slice == 0) {
+    if (h0->current_slice != 0) {
+        if (last_pic_structure != s->picture_structure ||
+            last_pic_dropable  != s->dropable) {
+            av_log(h->s.avctx, AV_LOG_ERROR,
+                   "Changing field mode (%d -> %d) between slices is not allowed\n",
+                   last_pic_structure, s->picture_structure);
+            s->picture_structure = last_pic_structure;
+            s->dropable          = last_pic_dropable;
+            return AVERROR_INVALIDDATA;
+        }
+    } else {
         /* Shorten frame num gaps so we don't have to allocate reference
          * frames just to throw them away */
         if (h->frame_num != h->prev_frame_num) {
@@ -3134,6 +3149,72 @@ static int decode_slice_header(H264Context *h, H264Context *h0)
             }
         }
 
+        /* See if we have a decoded first field looking for a pair...
+         * Here, we're using that to see if we should mark previously
+         * decode frames as "finished".
+         * We have to do that before the "dummy" in-between frame allocation,
+         * since that can modify s->current_picture_ptr. */
+        if (s0->first_field) {
+            assert(s0->current_picture_ptr);
+            assert(s0->current_picture_ptr->f.data[0]);
+            assert(s0->current_picture_ptr->f.reference != DELAYED_PIC_REF);
+
+            /* Mark old field/frame as completed */
+            if (!last_pic_dropable && s0->current_picture_ptr->owner2 == s0) {
+                ff_thread_report_progress(&s0->current_picture_ptr->f, INT_MAX,
+                                          last_pic_structure == PICT_BOTTOM_FIELD);
+            }
+
+            /* figure out if we have a complementary field pair */
+            if (!FIELD_PICTURE || s->picture_structure == last_pic_structure) {
+                /* Previous field is unmatched. Don't display it, but let it
+                 * remain for reference if marked as such. */
+                if (!last_pic_dropable && last_pic_structure != PICT_FRAME) {
+                    ff_thread_report_progress(&s0->current_picture_ptr->f, INT_MAX,
+                                              last_pic_structure == PICT_TOP_FIELD);
+                }
+            } else {
+                if (s0->current_picture_ptr->frame_num != h->frame_num) {
+                    /* This and previous field were reference, but had
+                     * different frame_nums. Consider this field first in
+                     * pair. Throw away previous field except for reference
+                     * purposes. */
+                    if (!last_pic_dropable && last_pic_structure != PICT_FRAME) {
+                        ff_thread_report_progress(&s0->current_picture_ptr->f, INT_MAX,
+                                                  last_pic_structure == PICT_TOP_FIELD);
+                    }
+                } else {
+                    /* Second field in complementary pair */
+                    if (!((last_pic_structure   == PICT_TOP_FIELD &&
+                           s->picture_structure == PICT_BOTTOM_FIELD) ||
+                          (last_pic_structure   == PICT_BOTTOM_FIELD &&
+                           s->picture_structure == PICT_TOP_FIELD))) {
+                        av_log(s->avctx, AV_LOG_ERROR,
+                               "Invalid field mode combination %d/%d\n",
+                               last_pic_structure, s->picture_structure);
+                        s->picture_structure = last_pic_structure;
+                        s->dropable          = last_pic_dropable;
+                        return AVERROR_INVALIDDATA;
+                    } else if (last_pic_dropable != s->dropable) {
+                        av_log(s->avctx, AV_LOG_ERROR,
+                               "Cannot combine reference and non-reference fields in the same frame\n");
+                        av_log_ask_for_sample(s->avctx, NULL);
+                        s->picture_structure = last_pic_structure;
+                        s->dropable          = last_pic_dropable;
+                        return AVERROR_INVALIDDATA;
+                    }
+
+                    /* Take ownership of this buffer. Note that if another thread owned
+                     * the first field of this buffer, we're not operating on that pointer,
+                     * so the original thread is still responsible for reporting progress
+                     * on that first field (or if that was us, we just did that above).
+                     * By taking ownership, we assign responsibility to ourselves to
+                     * report progress on the second field. */
+                    s0->current_picture_ptr->owner2 = s0;
+                }
+            }
+        }
+
         while (h->frame_num != h->prev_frame_num &&
                h->frame_num != (h->prev_frame_num + 1) % (1 << h->sps.log2_max_frame_num)) {
             Picture *prev = h->short_ref_count ? h->short_ref[0] : NULL;
@@ -3167,7 +3248,9 @@ static int decode_slice_header(H264Context *h, H264Context *h0)
             }
         }
 
-        /* See if we have a decoded first field looking for a pair... */
+        /* See if we have a decoded first field looking for a pair...
+         * We're using that to see whether to continue decoding in that
+         * frame, or to allocate a new one. */
         if (s0->first_field) {
             assert(s0->current_picture_ptr);
             assert(s0->current_picture_ptr->f.data[0]);
@@ -3180,12 +3263,10 @@ static int decode_slice_header(H264Context *h, H264Context *h0)
                 s0->current_picture_ptr = NULL;
                 s0->first_field         = FIELD_PICTURE;
             } else {
-                if (h->nal_ref_idc &&
+                if (s0->current_picture_ptr->frame_num != h->frame_num) {
-                    s0->current_picture_ptr->f.reference &&
+                    /* This and the previous field had different frame_nums.
-                    s0->current_picture_ptr->frame_num != h->frame_num) {
+                     * Consider this field first in pair. Throw away previous
-                    /* This and the previous field were reference, but had
+                     * one except for reference purposes. */
-                     * different frame_nums. Consider this field first in pair.
-                     * Throw away previous one except for reference purposes. */
                     s0->first_field         = 1;
                     s0->current_picture_ptr = NULL;
                 } else {
@@ -4129,8 +4210,10 @@ static int decode_nal_units(H264Context *h, const uint8_t *buf, int buf_size)
 
             ptr = ff_h264_decode_nal(hx, buf + buf_index, &dst_length,
                                      &consumed, next_avc - buf_index);
-            if (ptr == NULL || dst_length < 0)
+            if (ptr == NULL || dst_length < 0) {
-                return -1;
+                buf_index = -1;
+                goto end;
+            }
             i = buf_index + consumed;
             if ((s->workaround_bugs & FF_BUG_AUTODETECT) && i + 3 < next_avc &&
                 buf[i]     == 0x00 && buf[i + 1] == 0x00 &&
@@ -4187,7 +4270,8 @@ again:
                 if (h->nal_unit_type != NAL_IDR_SLICE) {
                     av_log(h->s.avctx, AV_LOG_ERROR,
                            "Invalid mix of idr and non-idr slices");
-                    return -1;
+                    buf_index = -1;
+                    goto end;
                 }
                 idr(h); // FIXME ensure we don't lose some frames if there is reordering
             case NAL_SLICE:
@@ -4311,7 +4395,8 @@ again:
                         av_log(avctx, AV_LOG_ERROR,
                                "Unsupported bit depth: %d\n",
                                h->sps.bit_depth_luma);
-                        return -1;
+                        buf_index = -1;
+                        goto end;
                     }
                 }
                 break;
@@ -4352,6 +4437,15 @@ again:
     }
     if (context_count)
         execute_decode_slices(h, context_count);
+
+end:
+    /* clean up */
+    if (s->current_picture_ptr && s->current_picture_ptr->owner2 == s &&
+        !s->dropable) {
+        ff_thread_report_progress(&s->current_picture_ptr->f, INT_MAX,
+                                  s->picture_structure == PICT_BOTTOM_FIELD);
+    }
+
     return buf_index;
 }