debuginfod: Check result of calling MHD_add_response_header.

Message ID 20211201113847.15352-1-mark@klomp.org
State Superseded
Headers
Series debuginfod: Check result of calling MHD_add_response_header. |

Commit Message

Mark Wielaard Dec. 1, 2021, 11:38 a.m. UTC
  Although unlikely the MHD_add_response_header can fail for
various reasons.  If it fails something odd is going on.
So check we can actually add a response header before using
the response.

Signed-off-by: Mark Wielaard <mark@klomp.org>
---
 debuginfod/ChangeLog      |  10 +++
 debuginfod/debuginfod.cxx | 127 ++++++++++++++++++++++++++++----------
 2 files changed, 105 insertions(+), 32 deletions(-)
  

Comments

Frank Ch. Eigler Dec. 1, 2021, 12:02 p.m. UTC | #1
Hi -

> Although unlikely the MHD_add_response_header can fail for
> various reasons.  If it fails something odd is going on.
> So check we can actually add a response header before using
> the response.

ISTM it is okay to send the response object (the body), even if
something goes wrong with adding optional headers later.


- FChE
  
Mark Wielaard Dec. 1, 2021, 12:24 p.m. UTC | #2
H Frank,

On Wed, 2021-12-01 at 07:02 -0500, Frank Ch. Eigler wrote:
> Although unlikely the MHD_add_response_header can fail for
> > various reasons.  If it fails something odd is going on.
> > So check we can actually add a response header before using
> > the response.
> 
> ISTM it is okay to send the response object (the body), even if
> something goes wrong with adding optional headers later.

OK, so log error, but proceed sending the response with the data
already added. I'll update my patch to do that instead. I don't really
think this will really fail often (or at all). But if it does, it would
be good to be able to catch it.

Thanks,

Mark
  

Patch

diff --git a/debuginfod/ChangeLog b/debuginfod/ChangeLog
index 822bd637..7054fdad 100644
--- a/debuginfod/ChangeLog
+++ b/debuginfod/ChangeLog
@@ -1,3 +1,13 @@ 
+2021-12-01  Mark Wielaard  <mark@klomp.org>
+
+	* debuginfod.cxx (reportable_exception::mhd_send_response): Check
+	MHD_add_response_header result.
+	(add_mhd_last_modified): Likewise and return true when successful.
+	(handle_buildid_f_match): Check MHD_add_response_header result.
+	(handle_buildid_r_match): Likewise.
+	(handle_metrics): Likewise.
+	(handle_root): Likewise.
+
 2021-11-10  √Črico N. Rolim  <erico.erc@gmail.com>
 
 	* debuginfod.cxx: include "system.h" under 'extern "C"' block.
diff --git a/debuginfod/debuginfod.cxx b/debuginfod/debuginfod.cxx
index 764e7b94..3b4591dd 100644
--- a/debuginfod/debuginfod.cxx
+++ b/debuginfod/debuginfod.cxx
@@ -1,5 +1,6 @@ 
 /* Debuginfo-over-http server.
    Copyright (C) 2019-2021 Red Hat, Inc.
+   Copyright (C) 2021 Mark J. Wielaard <mark@klomp.org>
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -646,8 +647,10 @@  struct reportable_exception
     MHD_Response* r = MHD_create_response_from_buffer (message.size(),
                                                        (void*) message.c_str(),
                                                        MHD_RESPMEM_MUST_COPY);
-    MHD_add_response_header (r, "Content-Type", "text/plain");
-    MHD_RESULT rc = MHD_queue_response (c, code, r);
+    MHD_RESULT rc;
+    rc = MHD_add_response_header (r, "Content-Type", "text/plain");
+    if (rc != MHD_NO)
+      rc = MHD_queue_response (c, code, r);
     MHD_destroy_response (r);
     return rc;
   }
@@ -1067,7 +1070,10 @@  conninfo (struct MHD_Connection * conn)
 ////////////////////////////////////////////////////////////////////////
 
 
-static void
+/* Adds a Last-Modified and Cache-Control header to the response.
+   Returns true when headers could be added, false when an error
+   occured adding an header.  */
+static bool
 add_mhd_last_modified (struct MHD_Response *resp, time_t mtime)
 {
   struct tm *now = gmtime (&mtime);
@@ -1076,10 +1082,14 @@  add_mhd_last_modified (struct MHD_Response *resp, time_t mtime)
       char datebuf[80];
       size_t rc = strftime (datebuf, sizeof (datebuf), "%a, %d %b %Y %T GMT", now);
       if (rc > 0 && rc < sizeof (datebuf))
-        (void) MHD_add_response_header (resp, "Last-Modified", datebuf);
+        if (MHD_add_response_header (resp, "Last-Modified", datebuf) == MHD_NO)
+	  return false;
     }
 
-  (void) MHD_add_response_header (resp, "Cache-Control", "public");
+  if (MHD_add_response_header (resp, "Cache-Control", "public") == MHD_NO)
+    return false;
+
+  return true;
 }
 
 
@@ -1125,11 +1135,22 @@  handle_buildid_f_match (bool internal_req_t,
     }
   else
     {
-      MHD_add_response_header (r, "Content-Type", "application/octet-stream");
       std::string file = b_source0.substr(b_source0.find_last_of("/")+1, b_source0.length());
-      MHD_add_response_header (r, "X-DEBUGINFOD-SIZE", to_string(s.st_size).c_str() );
-      MHD_add_response_header (r, "X-DEBUGINFOD-FILE", file.c_str() );
-      add_mhd_last_modified (r, s.st_mtime);
+      if (MHD_add_response_header (r, "Content-Type",
+				   "application/octet-stream") == MHD_NO
+	  || MHD_add_response_header (r, "X-DEBUGINFOD-SIZE",
+				      to_string(s.st_size).c_str()) == MHD_NO
+	  || MHD_add_response_header (r, "X-DEBUGINFOD-FILE",
+				      file.c_str()) == MHD_NO
+	  || add_mhd_last_modified (r, s.st_mtime) == false)
+	{
+	  if (verbose)
+	    obatched(clog) << "cannot add response headers for "
+			   << b_source0 << endl;
+	  close (fd);
+	  MHD_destroy_response (r);
+	  return NULL;
+	}
       if (verbose > 1)
         obatched(clog) << "serving file " << b_source0 << endl;
       /* libmicrohttpd will close it. */
@@ -1595,13 +1616,25 @@  handle_buildid_r_match (bool internal_req_p,
           break; // branch out of if "loop", to try new libarchive fetch attempt
         }
 
+      if (MHD_add_response_header (r, "Content-Type",
+				   "application/octet-stream") == MHD_NO
+	  || MHD_add_response_header (r, "X-DEBUGINFOD-SIZE",
+				      to_string(fs.st_size).c_str()) == MHD_NO
+	  || MHD_add_response_header (r, "X-DEBUGINFOD-ARCHIVE",
+				      b_source0.c_str()) == MHD_NO
+	  || MHD_add_response_header (r, "X-DEBUGINFOD-FILE",
+				      b_source1.c_str()) == MHD_NO
+	  || add_mhd_last_modified (r, fs.st_mtime))
+	{
+          if (verbose)
+            obatched(clog) << "cannot add response header for "
+			   << b_source0 << endl;
+	  close (fd);
+	  break; // branch out of if "loop", try new libarchive fetch attempt
+	}
+
       inc_metric ("http_responses_total","result","archive fdcache");
 
-      MHD_add_response_header (r, "Content-Type", "application/octet-stream");
-      MHD_add_response_header (r, "X-DEBUGINFOD-SIZE", to_string(fs.st_size).c_str());
-      MHD_add_response_header (r, "X-DEBUGINFOD-ARCHIVE", b_source0.c_str());
-      MHD_add_response_header (r, "X-DEBUGINFOD-FILE", b_source1.c_str());
-      add_mhd_last_modified (r, fs.st_mtime);
       if (verbose > 1)
         obatched(clog) << "serving fdcache archive " << b_source0 << " file " << b_source1 << endl;
       /* libmicrohttpd will close it. */
@@ -1741,13 +1774,25 @@  handle_buildid_r_match (bool internal_req_p,
         }
       else
         {
-          MHD_add_response_header (r, "Content-Type", "application/octet-stream");
           std::string file = b_source1.substr(b_source1.find_last_of("/")+1, b_source1.length());
-          MHD_add_response_header (r, "X-DEBUGINFOD-SIZE", to_string(fs.st_size).c_str());
-          MHD_add_response_header (r, "X-DEBUGINFOD-ARCHIVE", b_source0.c_str());
-          MHD_add_response_header (r, "X-DEBUGINFOD-FILE", file.c_str());
-
-          add_mhd_last_modified (r, archive_entry_mtime(e));
+          if (MHD_add_response_header (r, "Content-Type",
+				       "application/octet-stream") == MHD_NO
+	      || MHD_add_response_header (r, "X-DEBUGINFOD-SIZE",
+					  to_string(fs.st_size).c_str()) == MHD_NO
+	      || MHD_add_response_header (r, "X-DEBUGINFOD-ARCHIVE",
+					  b_source0.c_str()) == MHD_NO
+	      || MHD_add_response_header (r, "X-DEBUGINFOD-FILE",
+					  file.c_str()) == MHD_NO
+	      || add_mhd_last_modified (r, archive_entry_mtime(e)) == false)
+	    {
+	      if (verbose)
+		obatched(clog) << "cannot create response header for "
+			       << b_source0 << endl;
+	      close(fd);
+	      MHD_destroy_response (r);
+	      r = NULL;
+	      break; // assume no chance of better luck around another iteration; no other copies of same file
+	    }
           if (verbose > 1)
             obatched(clog) << "serving archive " << b_source0 << " file " << b_source1 << endl;
           /* libmicrohttpd will close it. */
@@ -2012,14 +2057,18 @@  and will not query the upstream servers");
           auto r = MHD_create_response_from_fd ((uint64_t) s.st_size, fd);
           if (r)
             {
-              MHD_add_response_header (r, "Content-Type", "application/octet-stream");
-              add_mhd_last_modified (r, s.st_mtime);
-              if (verbose > 1)
-                obatched(clog) << "serving file from upstream debuginfod/cache" << endl;
-              if (result_fd)
-                *result_fd = fd;
-              return r; // NB: don't close fd; libmicrohttpd will
-            }
+              if (MHD_add_response_header (r, "Content-Type",
+					   "application/octet-stream") != MHD_NO
+		  && add_mhd_last_modified (r, s.st_mtime) != false)
+		{
+		  if (verbose > 1)
+		    obatched(clog) << "serving file from upstream debuginfod/cache" << endl;
+		  if (result_fd)
+		    *result_fd = fd;
+		  return r; // NB: don't close fd; libmicrohttpd will
+		}
+	      MHD_destroy_response (r);
+	    }
         }
       close (fd);
     }
@@ -2163,8 +2212,15 @@  handle_metrics (off_t* size)
   MHD_Response* r = MHD_create_response_from_buffer (os.size(),
                                                      (void*) os.c_str(),
                                                      MHD_RESPMEM_MUST_COPY);
-  *size = os.size();
-  MHD_add_response_header (r, "Content-Type", "text/plain");
+  if (r != NULL)
+    {
+      *size = os.size();
+      if (MHD_add_response_header (r, "Content-Type", "text/plain") == MHD_NO)
+	{
+	  MHD_destroy_response (r);
+	  r = NULL;
+	}
+    }
   return r;
 }
 
@@ -2176,8 +2232,15 @@  handle_root (off_t* size)
   MHD_Response* r = MHD_create_response_from_buffer (version.size (),
 						     (void *) version.c_str (),
 						     MHD_RESPMEM_PERSISTENT);
-  *size = version.size ();
-  MHD_add_response_header (r, "Content-Type", "text/plain");
+  if (r != NULL)
+    {
+      *size = version.size ();
+      if (MHD_add_response_header (r, "Content-Type", "text/plain") == MHD_NO)
+	{
+	  MHD_destroy_response (r);
+	  r = NULL;
+	}
+    }
   return r;
 }