libavutil/encryption_info: Allow multiple init info.

It is possible for there to be multiple encryption init info structure.
For example, to support multiple key systems or in key rotation.  This
changes the AVEncryptionInitInfo struct to be a linked list so there
can be multiple structs without breaking ABI.
Signed-off-by: Jacob Trimble <modmaker@google.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/encryption_info.c

@@ -160,13 +160,16 @@ uint8_t *av_encryption_info_add_side_data(const AVEncryptionInfo *info, size_t *
 }
 
 // The format of the AVEncryptionInitInfo side data:
-// u32be system_id_size
-// u32be num_key_ids
-// u32be key_id_size
-// u32be data_size
-// u8[system_id_size] system_id
-// u8[key_id_size][num_key_id] key_ids
-// u8[data_size] data
+// u32be init_info_count
+// {
+//   u32be system_id_size
+//   u32be num_key_ids
+//   u32be key_id_size
+//   u32be data_size
+//   u8[system_id_size] system_id
+//   u8[key_id_size][num_key_id] key_ids
+//   u8[data_size] data
+// }[init_info_count]
 
 #define FF_ENCRYPTION_INIT_INFO_EXTRA 16
 
@@ -215,6 +218,7 @@ void av_encryption_init_info_free(AVEncryptionInitInfo *info)
         for (i = 0; i < info->num_key_ids; i++) {
             av_free(info->key_ids[i]);
         }
+        av_encryption_init_info_free(info->next);
         av_free(info->system_id);
         av_free(info->key_ids);
         av_free(info->data);
@@ -225,71 +229,111 @@ void av_encryption_init_info_free(AVEncryptionInitInfo *info)
 AVEncryptionInitInfo *av_encryption_init_info_get_side_data(
     const uint8_t *side_data, size_t side_data_size)
 {
-    AVEncryptionInitInfo *info;
-    uint64_t system_id_size, num_key_ids, key_id_size, data_size, i;
+    // |ret| tracks the front of the list, |info| tracks the back.
+    AVEncryptionInitInfo *ret = NULL, *info, *temp_info;
+    uint64_t system_id_size, num_key_ids, key_id_size, data_size, i, j;
+    uint64_t init_info_count;
 
-    if (!side_data || side_data_size < FF_ENCRYPTION_INIT_INFO_EXTRA)
+    if (!side_data || side_data_size < 4)
         return NULL;
 
-    system_id_size = AV_RB32(side_data);
-    num_key_ids = AV_RB32(side_data + 4);
-    key_id_size = AV_RB32(side_data + 8);
-    data_size = AV_RB32(side_data + 12);
+    init_info_count = AV_RB32(side_data);
+    side_data += 4;
+    side_data_size -= 4;
+    for (i = 0; i < init_info_count; i++) {
+        if (side_data_size < FF_ENCRYPTION_INIT_INFO_EXTRA) {
+            av_encryption_init_info_free(ret);
+            return NULL;
+        }
 
-    // UINT32_MAX + UINT32_MAX + UINT32_MAX * UINT32_MAX == UINT64_MAX
-    if (side_data_size - FF_ENCRYPTION_INIT_INFO_EXTRA < system_id_size + data_size + num_key_ids * key_id_size)
-        return NULL;
+        system_id_size = AV_RB32(side_data);
+        num_key_ids = AV_RB32(side_data + 4);
+        key_id_size = AV_RB32(side_data + 8);
+        data_size = AV_RB32(side_data + 12);
 
-    info = av_encryption_init_info_alloc(system_id_size, num_key_ids, key_id_size, data_size);
-    if (!info)
-        return NULL;
+        // UINT32_MAX + UINT32_MAX + UINT32_MAX * UINT32_MAX == UINT64_MAX
+        if (side_data_size - FF_ENCRYPTION_INIT_INFO_EXTRA < system_id_size + data_size + num_key_ids * key_id_size) {
+            av_encryption_init_info_free(ret);
+            return NULL;
+        }
+        side_data += FF_ENCRYPTION_INIT_INFO_EXTRA;
+        side_data_size -= FF_ENCRYPTION_INIT_INFO_EXTRA;
+
+        temp_info = av_encryption_init_info_alloc(system_id_size, num_key_ids, key_id_size, data_size);
+        if (!temp_info) {
+            av_encryption_init_info_free(ret);
+            return NULL;
+        }
+        if (i == 0) {
+            info = ret = temp_info;
+        } else {
+            info->next = temp_info;
+            info = temp_info;
+        }
 
-    memcpy(info->system_id, side_data + 16, system_id_size);
-    side_data += system_id_size + 16;
-    for (i = 0; i < num_key_ids; i++) {
-      memcpy(info->key_ids[i], side_data, key_id_size);
-      side_data += key_id_size;
+        memcpy(info->system_id, side_data, system_id_size);
+        side_data += system_id_size;
+        side_data_size -= system_id_size;
+        for (j = 0; j < num_key_ids; j++) {
+            memcpy(info->key_ids[j], side_data, key_id_size);
+            side_data += key_id_size;
+            side_data_size -= key_id_size;
+        }
+        memcpy(info->data, side_data, data_size);
+        side_data += data_size;
+        side_data_size -= data_size;
     }
-    memcpy(info->data, side_data, data_size);
 
-    return info;
+    return ret;
 }
 
 uint8_t *av_encryption_init_info_add_side_data(const AVEncryptionInitInfo *info, size_t *side_data_size)
 {
+    const AVEncryptionInitInfo *cur_info;
     uint8_t *buffer, *cur_buffer;
-    uint32_t i, max_size;
-
-    if (UINT32_MAX - FF_ENCRYPTION_INIT_INFO_EXTRA < info->system_id_size ||
-        UINT32_MAX - FF_ENCRYPTION_INIT_INFO_EXTRA - info->system_id_size < info->data_size) {
-        return NULL;
-    }
-
-    if (info->num_key_ids) {
-        max_size = UINT32_MAX - FF_ENCRYPTION_INIT_INFO_EXTRA - info->system_id_size - info->data_size;
-        if (max_size / info->num_key_ids < info->key_id_size)
+    uint32_t i, init_info_count;
+    uint64_t temp_side_data_size;
+
+    temp_side_data_size = 4;
+    init_info_count = 0;
+    for (cur_info = info; cur_info; cur_info = cur_info->next) {
+        temp_side_data_size += (uint64_t)FF_ENCRYPTION_INIT_INFO_EXTRA + info->system_id_size + info->data_size;
+        if (init_info_count == UINT32_MAX || temp_side_data_size > UINT32_MAX) {
             return NULL;
+        }
+        init_info_count++;
+
+        if (info->num_key_ids) {
+            temp_side_data_size += (uint64_t)info->num_key_ids * info->key_id_size;
+            if (temp_side_data_size > UINT32_MAX) {
+                return NULL;
+            }
+        }
     }
+    *side_data_size = temp_side_data_size;
 
-    *side_data_size = FF_ENCRYPTION_INIT_INFO_EXTRA + info->system_id_size +
-                      info->data_size + (info->num_key_ids * info->key_id_size);
     cur_buffer = buffer = av_malloc(*side_data_size);
     if (!buffer)
         return NULL;
 
-    AV_WB32(cur_buffer,      info->system_id_size);
-    AV_WB32(cur_buffer +  4, info->num_key_ids);
-    AV_WB32(cur_buffer +  8, info->key_id_size);
-    AV_WB32(cur_buffer + 12, info->data_size);
-    cur_buffer += 16;
-
-    memcpy(cur_buffer, info->system_id, info->system_id_size);
-    cur_buffer += info->system_id_size;
-    for (i = 0; i < info->num_key_ids; i++) {
-        memcpy(cur_buffer, info->key_ids[i], info->key_id_size);
-        cur_buffer += info->key_id_size;
+    AV_WB32(cur_buffer, init_info_count);
+    cur_buffer += 4;
+    for (cur_info = info; cur_info; cur_info = cur_info->next) {
+        AV_WB32(cur_buffer,      cur_info->system_id_size);
+        AV_WB32(cur_buffer +  4, cur_info->num_key_ids);
+        AV_WB32(cur_buffer +  8, cur_info->key_id_size);
+        AV_WB32(cur_buffer + 12, cur_info->data_size);
+        cur_buffer += 16;
+
+        memcpy(cur_buffer, cur_info->system_id, cur_info->system_id_size);
+        cur_buffer += cur_info->system_id_size;
+        for (i = 0; i < cur_info->num_key_ids; i++) {
+            memcpy(cur_buffer, cur_info->key_ids[i], cur_info->key_id_size);
+            cur_buffer += cur_info->key_id_size;
+        }
+        memcpy(cur_buffer, cur_info->data, cur_info->data_size);
+        cur_buffer += cur_info->data_size;
     }
-    memcpy(cur_buffer, info->data, info->data_size);
 
     return buffer;
 }

libavutil/encryption_info.h

@@ -115,6 +115,11 @@ typedef struct AVEncryptionInitInfo {
      */
     uint8_t* data;
     uint32_t data_size;
+
+    /**
+     * An optional pointer to the next initialization info in the list.
+     */
+    struct AVEncryptionInitInfo *next;
 } AVEncryptionInitInfo;
 
 /**