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changeset 7629:f47f7d3d1bfa

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Mp4: fixed possible chunk offset overflow. In "co64" atom chunk start offset is a 64-bit unsigned integer. When trimming the "mdat" atom, chunk offsets are casted to off_t values which are typically 64-bit signed integers. A specially crafted mp4 file with huge chunk offsets may lead to off_t overflow and result in negative trim boundaries. The consequences of the overflow are: - Incorrect Content-Length header value in the response. - Negative left boundary of the response file buffer holding the trimmed "mdat". This leads to pread()/sendfile() errors followed by closing the client connection. On rare systems where off_t is a 32-bit integer, this scenario is also feasible with the "stco" atom. The fix is to add checks which make sure data chunks referenced by each track are within the mp4 file boundaries. Additionally a few more checks are added to ensure mp4 file consistency and log errors.
author Roman Arutyunyan <arut@nginx.com>
date Wed, 26 Feb 2020 15:10:46 +0300
parents 2e3bfd696ecb
children f001d9384293
files src/http/modules/ngx_http_mp4_module.c
diffstat 1 files changed, 64 insertions(+), 11 deletions(-) [+]
line wrap: on
line diff
--- a/src/http/modules/ngx_http_mp4_module.c
+++ b/src/http/modules/ngx_http_mp4_module.c
@@ -3116,6 +3116,13 @@ ngx_http_mp4_update_stsz_atom(ngx_http_m
                        "chunk samples sizes:%uL",
                        trak->start_chunk_samples_size);
 
+        if (trak->start_chunk_samples_size > (uint64_t) mp4->end) {
+            ngx_log_error(NGX_LOG_ERR, mp4->file.log, 0,
+                          "too large mp4 start samples size in \"%s\"",
+                          mp4->file.name.data);
+            return NGX_ERROR;
+        }
+
         if (mp4->length) {
             if (trak->end_sample - trak->start_sample > entries) {
                 ngx_log_error(NGX_LOG_ERR, mp4->file.log, 0,
@@ -3135,6 +3142,13 @@ ngx_http_mp4_update_stsz_atom(ngx_http_m
             ngx_log_debug1(NGX_LOG_DEBUG_HTTP, mp4->file.log, 0,
                            "mp4 stsz end_chunk_samples_size:%uL",
                            trak->end_chunk_samples_size);
+
+            if (trak->end_chunk_samples_size > (uint64_t) mp4->end) {
+                ngx_log_error(NGX_LOG_ERR, mp4->file.log, 0,
+                              "too large mp4 end samples size in \"%s\"",
+                              mp4->file.name.data);
+                return NGX_ERROR;
+            }
         }
 
         atom_size = sizeof(ngx_mp4_stsz_atom_t) + (data->last - data->pos);
@@ -3226,6 +3240,7 @@ ngx_http_mp4_update_stco_atom(ngx_http_m
 {
     size_t                atom_size;
     uint32_t              entries;
+    uint64_t              chunk_offset, samples_size;
     ngx_buf_t            *atom, *data;
     ngx_mp4_stco_atom_t  *stco_atom;
 
@@ -3256,8 +3271,19 @@ ngx_http_mp4_update_stco_atom(ngx_http_m
 
     data->pos += trak->start_chunk * sizeof(uint32_t);
 
-    trak->start_offset = ngx_mp4_get_32value(data->pos);
-    trak->start_offset += trak->start_chunk_samples_size;
+    chunk_offset = ngx_mp4_get_32value(data->pos);
+    samples_size = trak->start_chunk_samples_size;
+
+    if (chunk_offset > (uint64_t) mp4->end - samples_size
+        || chunk_offset + samples_size > NGX_MAX_UINT32_VALUE)
+    {
+        ngx_log_error(NGX_LOG_ERR, mp4->file.log, 0,
+                      "too large chunk offset in \"%s\"",
+                      mp4->file.name.data);
+        return NGX_ERROR;
+    }
+
+    trak->start_offset = chunk_offset + samples_size;
     ngx_mp4_set_32value(data->pos, trak->start_offset);
 
     ngx_log_debug1(NGX_LOG_DEBUG_HTTP, mp4->file.log, 0,
@@ -3276,9 +3302,19 @@ ngx_http_mp4_update_stco_atom(ngx_http_m
         data->last = data->pos + entries * sizeof(uint32_t);
 
         if (entries) {
-            trak->end_offset =
-                            ngx_mp4_get_32value(data->last - sizeof(uint32_t));
-            trak->end_offset += trak->end_chunk_samples_size;
+            chunk_offset = ngx_mp4_get_32value(data->last - sizeof(uint32_t));
+            samples_size = trak->end_chunk_samples_size;
+
+            if (chunk_offset > (uint64_t) mp4->end - samples_size
+                || chunk_offset + samples_size > NGX_MAX_UINT32_VALUE)
+            {
+                ngx_log_error(NGX_LOG_ERR, mp4->file.log, 0,
+                              "too large chunk offset in \"%s\"",
+                              mp4->file.name.data);
+                return NGX_ERROR;
+            }
+
+            trak->end_offset = chunk_offset + samples_size;
 
             ngx_log_debug1(NGX_LOG_DEBUG_HTTP, mp4->file.log, 0,
                            "end chunk offset:%O", trak->end_offset);
@@ -3409,7 +3445,7 @@ ngx_http_mp4_update_co64_atom(ngx_http_m
     ngx_http_mp4_trak_t *trak)
 {
     size_t                atom_size;
-    uint64_t              entries;
+    uint64_t              entries, chunk_offset, samples_size;
     ngx_buf_t            *atom, *data;
     ngx_mp4_co64_atom_t  *co64_atom;
 
@@ -3440,8 +3476,17 @@ ngx_http_mp4_update_co64_atom(ngx_http_m
 
     data->pos += trak->start_chunk * sizeof(uint64_t);
 
-    trak->start_offset = ngx_mp4_get_64value(data->pos);
-    trak->start_offset += trak->start_chunk_samples_size;
+    chunk_offset = ngx_mp4_get_64value(data->pos);
+    samples_size = trak->start_chunk_samples_size;
+
+    if (chunk_offset > (uint64_t) mp4->end - samples_size) {
+        ngx_log_error(NGX_LOG_ERR, mp4->file.log, 0,
+                      "too large chunk offset in \"%s\"",
+                      mp4->file.name.data);
+        return NGX_ERROR;
+    }
+
+    trak->start_offset = chunk_offset + samples_size;
     ngx_mp4_set_64value(data->pos, trak->start_offset);
 
     ngx_log_debug1(NGX_LOG_DEBUG_HTTP, mp4->file.log, 0,
@@ -3460,9 +3505,17 @@ ngx_http_mp4_update_co64_atom(ngx_http_m
         data->last = data->pos + entries * sizeof(uint64_t);
 
         if (entries) {
-            trak->end_offset =
-                            ngx_mp4_get_64value(data->last - sizeof(uint64_t));
-            trak->end_offset += trak->end_chunk_samples_size;
+            chunk_offset = ngx_mp4_get_64value(data->last - sizeof(uint64_t));
+            samples_size = trak->end_chunk_samples_size;
+
+            if (chunk_offset > (uint64_t) mp4->end - samples_size) {
+                ngx_log_error(NGX_LOG_ERR, mp4->file.log, 0,
+                              "too large chunk offset in \"%s\"",
+                              mp4->file.name.data);
+                return NGX_ERROR;
+            }
+
+            trak->end_offset = chunk_offset + samples_size;
 
             ngx_log_debug1(NGX_LOG_DEBUG_HTTP, mp4->file.log, 0,
                            "end chunk offset:%O", trak->end_offset);