Fixing memory allocation error in ngx_rtmp_live_join()

[Fahnenfluchtige]

The Svace static analysis tool identified a potential issue in the function ngx_rtmp_live_join(), where the return value of ngx_palloc() is used without NULL-checking (506-510):

if (ctx == NULL) {
        ctx = ngx_palloc(s->connection->pool, sizeof(ngx_rtmp_live_ctx_t)); // ngx_palloc may return NULL
        ngx_rtmp_set_ctx(s, ctx, ngx_rtmp_live_module);
    }

ngx_memzero(ctx, sizeof(*ctx)); 

ngx_palloc() is guaranteed not to return NULL only if there is enough space available in at least one of the existing memory pools in the linked list (see the implementation of ngx_palloc_small()). However, this guarantee is not absolute. If there is no available space, memory allocation will proceed by calling ngx_palloc_block(), which then invokes ngx_memalign() or posix_memalign()/memalign() to allocate memory. These system calls can return NULL if allocation fails. Therefore, it is always recommended to check the return value of ngx_palloc() and similar functions before using the allocated memory.

So it's necessary to add NULL-checking:

diff --git a/ngx_rtmp_live_module.c b/ngx_rtmp_live_module.c
index 5bebb9e..3826e8e 100644
--- a/ngx_rtmp_live_module.c
+++ b/ngx_rtmp_live_module.c
@@ -504,6 +504,19 @@ ngx_rtmp_live_join(ngx_rtmp_session_t *s, u_char *name, unsigned publisher)
 
     if (ctx == NULL) {
         ctx = ngx_palloc(s->connection->pool, sizeof(ngx_rtmp_live_ctx_t));
+        
+        if (ctx == NULL) {
+            ngx_log_error(NGX_LOG_ERR, s->connection->log, 0,
+                          "live: failed to allocate memory for context");
+
+            ngx_rtmp_send_status(s, "NetStream.Play.Failed", "error",
+                                 "Failed to allocate memory");
+
+            ngx_rtmp_finalize_session(s); 
+
+            return;
+        }
+
         ngx_rtmp_set_ctx(s, ctx, ngx_rtmp_live_module);
     }