[PATCH 1/3] debuginfod: Make sure debuginfod_config_cache always returns valid stat

[Mark Wielaard]

If the condig file which value was requested from
debuginfod_config_cache didn't exist yet, stat would fail and no valid
struct stat would be returned even when the file was correctly
created. Fix this by always using O_CREAT to open the file, and reuse
that file descriptor to call fstat and for either writing the default
value or reading the config file value.

Signed-off-by: Mark Wielaard <m...@klomp.org>
---
 debuginfod/ChangeLog           |  6 ++++++
 debuginfod/debuginfod-client.c | 21 ++++++++++++++-------
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/debuginfod/ChangeLog b/debuginfod/ChangeLog
index 257ac39f..46a6e22b 100644
--- a/debuginfod/ChangeLog
+++ b/debuginfod/ChangeLog
@@ -1,3 +1,9 @@
+2022-05-09  Mark Wielaard  <m...@klomp.org>
+
+       * debuginfod-client.c (debuginfod_config_cache): Always open with
+       O_CREATE first, then use fstat, only write the cache_config_default_s
+       value if st_size == 0, otherwise read value from file.
+
 2022-05-09  Mark Wielaard  <m...@klomp.org>
 
        * debuginfod.cxx (conninfo): Always provide servname to getnameinfo.
diff --git a/debuginfod/debuginfod-client.c b/debuginfod/debuginfod-client.c
index 89208216..3b2728f1 100644
--- a/debuginfod/debuginfod-client.c
+++ b/debuginfod/debuginfod-client.c
@@ -235,14 +235,19 @@ debuginfod_config_cache(char *config_path,
                        long cache_config_default_s,
                        struct stat *st)
 {
-  int fd;
-  /* if the config file doesn't exist, create one with DEFFILEMODE*/
-  if(stat(config_path, st) == -1)
+  int fd = open(config_path, O_CREAT | O_RDWR, DEFFILEMODE);
+  if (fd < 0)
+    return -errno;
+
+  if (fstat (fd, st) < 0)
     {
-      fd = open(config_path, O_CREAT | O_RDWR, DEFFILEMODE);
-      if (fd < 0)
-        return -errno;
+      int ret = -errno;
+      close (fd);
+      return ret;
+    }
 
+  if (st->st_size == 0)
+    {
       if (dprintf(fd, "%ld", cache_config_default_s) < 0)
        {
          int ret = -errno;
@@ -251,10 +256,11 @@ debuginfod_config_cache(char *config_path,
        }
 
       close (fd);
+      return cache_config_default_s;
     }
 
   long cache_config;
-  FILE *config_file = fopen(config_path, "r");
+  FILE *config_file = fdopen(fd, "r");
   if (config_file)
     {
       if (fscanf(config_file, "%ld", &cache_config) != 1)
@@ -264,6 +270,7 @@ debuginfod_config_cache(char *config_path,
   else
     cache_config = cache_config_default_s;
 
+  close (fd);
   return cache_config;
 }
 
-- 
2.30.2