[nginx] Truncation detection in sendfile() on Linux.

[Maxim Dounin]

details:   http://hg.nginx.org/nginx/rev/4df3d9fcdee8
branches:  
changeset: 6437:4df3d9fcdee8
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Tue Mar 15 18:26:17 2016 +0300
description:
Truncation detection in sendfile() on Linux.

This addresses connection hangs as observed in ticket #504, and
CPU hogs with "aio threads; sendfile on" as reported in the mailing list,
see http://mailman.nginx.org/pipermail/nginx-ru/2016-March/057638.html.

The alert is identical to one used on FreeBSD.

diffstat:

 src/os/unix/ngx_linux_sendfile_chain.c |  26 ++++++++++++++++++++++++++
 1 files changed, 26 insertions(+), 0 deletions(-)

diffs (43 lines):

diff --git a/src/os/unix/ngx_linux_sendfile_chain.c b/src/os/unix/ngx_linux_sendfile_chain.c
--- a/src/os/unix/ngx_linux_sendfile_chain.c
+++ b/src/os/unix/ngx_linux_sendfile_chain.c
@@ -292,6 +292,19 @@ eintr:
         }
     }
 
+    if (n == 0) {
+        /*
+         * if sendfile returns zero, then someone has truncated the file,
+         * so the offset became beyond the end of the file
+         */
+
+        ngx_log_error(NGX_LOG_ALERT, c->log, 0,
+                      "sendfile() reported that \"%s\" was truncated at %O",
+                      file->file->name.data, file->file_pos);
+
+        return NGX_ERROR;
+    }
+
     ngx_log_debug3(NGX_LOG_DEBUG_EVENT, c->log, 0, "sendfile: %z of %uz @%O",
                    n, size, file->file_pos);
 
@@ -354,6 +367,19 @@ ngx_linux_sendfile_thread(ngx_connection
             return NGX_ERROR;
         }
 
+        if (ctx->sent == 0) {
+            /*
+             * if sendfile returns zero, then someone has truncated the file,
+             * so the offset became beyond the end of the file
+             */
+
+            ngx_log_error(NGX_LOG_ALERT, c->log, 0,
+                          "sendfile() reported that \"%s\" was truncated at %O",
+                          file->file->name.data, file->file_pos);
+
+            return NGX_ERROR;
+        }
+
         *sent = ctx->sent;
 
         return (ctx->sent == ctx->size) ? NGX_DONE : NGX_AGAIN;