commit 3dcaacec0a2bc751711157b9deacc5c2262f23c4
author Roman Arutyunyan <arut@nginx.com> Tue Aug 22 21:22:59 2017 +0300
committer Roman Arutyunyan <arut@nginx.com> Tue Aug 22 21:22:59 2017 +0300
tree dd3f1bf912626dfc44915c2d2c1692d454a71f7c
parent 5dcd929b75aae09c14967b2557ed16d903fa1a09

Secure link: fixed stack buffer overflow.

When secure link checksum has length of 23 or 24 bytes, decoded base64 value
could occupy 17 or 18 bytes which is more than 16 bytes previously allocated
for it on stack.  The buffer overflow does not have any security implications
since only one local variable was corrupted and this variable was not used in
this case.

The fix is to increase buffer size up to 18 bytes.  Useless buffer size
initialization is removed as well.

src/http/modules/ngx_http_secure_link_module.c

diff --git a/src/http/modules/ngx_http_secure_link_module.c b/src/http/modules/ngx_http_secure_link_module.c
index 907ba6e..536e09a 100644
--- a/src/http/modules/ngx_http_secure_link_module.c
+++ b/src/http/modules/ngx_http_secure_link_module.c
@@ -107,7 +107,7 @@
     ngx_md5_t                     md5;
     ngx_http_secure_link_ctx_t   *ctx;
     ngx_http_secure_link_conf_t  *conf;
-    u_char                        hash_buf[16], md5_buf[16];
+    u_char                        hash_buf[18], md5_buf[16];
 
     conf = ngx_http_get_module_loc_conf(r, ngx_http_secure_link_module);
 
@@ -154,7 +154,6 @@
         goto not_found;
     }
 
-    hash.len = 16;
     hash.data = hash_buf;
 
     if (ngx_decode_base64url(&hash, &val) != NGX_OK) {