[glibc/fw/bug25420] resolv: Enhance __resolv_conf_load to capture file change data

[glibc/fw/bug25420] resolv: Enhance __resolv_conf_load to capture file change data

[Florian Weimer]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=dd0b4df329ff7ff2a656404db271c8ee8379ff9d

commit dd0b4df329ff7ff2a656404db271c8ee8379ff9d
Author: Florian Weimer <fweimer@redhat.com>
Date:   Tue Jan 21 17:25:39 2020 +0100

    resolv: Enhance __resolv_conf_load to capture file change data
    
    The data is captured after reading the file.  This allows callers
    to check the change data against an earlier measurement.
    
    Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

Diff:
---
 resolv/res_init.c    | 14 +++++++++++---
 resolv/resolv_conf.c |  2 +-
 resolv/resolv_conf.h | 10 +++++++---
 3 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/resolv/res_init.c b/resolv/res_init.c
index 0934571..98d84f2 100644
--- a/resolv/res_init.c
+++ b/resolv/res_init.c
@@ -103,6 +103,7 @@
 #include <inet/net-internal.h>
 #include <errno.h>
 #include <resolv_conf.h>
+#include <file_change_detection.h>
 
 static uint32_t net_mask (struct in_addr);
 
@@ -549,7 +550,8 @@ res_vinit_1 (FILE *fp, struct resolv_conf_parser *parser)
 }
 
 struct resolv_conf *
-__resolv_conf_load (struct __res_state *preinit)
+__resolv_conf_load (struct __res_state *preinit,
+                    struct file_change_detection *change)
 {
   /* Ensure that /etc/hosts.conf has been loaded (once).  */
   _res_hconf_init ();
@@ -577,7 +579,13 @@ __resolv_conf_load (struct __res_state *preinit)
   resolv_conf_parser_init (&parser, preinit);
 
   struct resolv_conf *conf = NULL;
-  if (res_vinit_1 (fp, &parser))
+  bool ok = res_vinit_1 (fp, &parser);
+  if (ok && change != NULL)
+    /* Update the file change information if the configuration was
+       loaded successfully.  */
+    ok = file_change_detection_for_fp (change, fp);
+
+  if (ok)
     {
       parser.template.nameserver_list
         = nameserver_list_begin (&parser.nameserver_list);
@@ -615,7 +623,7 @@ __res_vinit (res_state statp, int preinit)
   if (preinit && has_preinit_values (statp))
     /* For the preinit case, we cannot use the cached configuration
        because some settings could be different.  */
-    conf = __resolv_conf_load (statp);
+    conf = __resolv_conf_load (statp, NULL);
   else
     conf = __resolv_conf_get_current ();
   if (conf == NULL)
diff --git a/resolv/resolv_conf.c b/resolv/resolv_conf.c
index d954ba9..bdd2ebb 100644
--- a/resolv/resolv_conf.c
+++ b/resolv/resolv_conf.c
@@ -136,7 +136,7 @@ __resolv_conf_get_current (void)
     {
       /* Parse configuration while holding the lock.  This avoids
          duplicate work.  */
-      conf = __resolv_conf_load (NULL);
+      conf = __resolv_conf_load (NULL, NULL);
       if (conf != NULL)
         {
           if (global_copy->conf_current != NULL)
diff --git a/resolv/resolv_conf.h b/resolv/resolv_conf.h
index 01cbff9..101e14b 100644
--- a/resolv/resolv_conf.h
+++ b/resolv/resolv_conf.h
@@ -63,12 +63,16 @@ struct resolv_conf
    and the struct resolv_context facility.  */
 
 struct __res_state;
+struct file_change_detection;
 
 /* Read /etc/resolv.conf and return a configuration object, or NULL if
    /etc/resolv.conf cannot be read due to memory allocation errors.
-   If PREINIT is not NULL, some configuration values are taken from the
-   struct __res_state object.  */
-struct resolv_conf *__resolv_conf_load (struct __res_state *preinit)
+   If PREINIT is not NULL, some configuration values are taken from
+   the struct __res_state object.  If CHANGE is not null, file change
+   detection data is written to *CHANGE, based on the state of the
+   file after reading it.  */
+struct resolv_conf *__resolv_conf_load (struct __res_state *preinit,
+                                        struct file_change_detection *change)
   attribute_hidden __attribute__ ((warn_unused_result));
 
 /* Return a configuration object for the current /etc/resolv.conf