chrony/0001-main-create-new-file-when-writing-pidfile.patch

From f00fed20092b6a42283f29c6ee1f58244d74b545 Mon Sep 17 00:00:00 2001
From: Miroslav Lichvar <mlichvar@redhat.com>
Date: Thu, 6 Aug 2020 09:31:11 +0200
Subject: [PATCH] main: create new file when writing pidfile

When writing the pidfile, open the file with the O_CREAT|O_EXCL flags
to avoid following a symlink and writing the PID to an unexpected file,
when chronyd still has the root privileges.

The Linux open(2) man page warns about O_EXCL not working as expected on
NFS versions before 3 and Linux versions before 2.6. Saving pidfiles on
a distributed filesystem like NFS is not generally expected, but if
there is a reason to do that, these old kernel and NFS versions are not
considered to be supported for saving files by chronyd.

This is a minimal backport specific to this issue of the following
commits:
- commit 2fc8edacb810 ("use PATH_MAX")
- commit f4c6a00b2a11 ("logging: call exit() in LOG_Message()")
- commit 7a4c396bba8f ("util: add functions for common file operations")
- commit e18903a6b563 ("switch to new util file functions")

Reported-by: Matthias Gerstner <mgerstner@suse.de>
---
 logging.c |  1 +
 main.c    | 10 ++-----
 sysincl.h |  1 +
 util.c    | 95 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 util.h    | 11 ++++++++
 5 files changed, 111 insertions(+), 7 deletions(-)

diff --git a/logging.c b/logging.c
index d2296e0..fd7f900 100644
--- a/logging.c
+++ b/logging.c
@@ -171,6 +171,7 @@ void LOG_Message(LOG_Severity severity,
         system_log = 0;
         log_message(1, severity, buf);
       }
+      exit(1);
       break;
     default:
       assert(0);
diff --git a/main.c b/main.c
index 6ccf32e..8edb2e1 100644
--- a/main.c
+++ b/main.c
@@ -281,13 +281,9 @@ write_pidfile(void)
   if (!pidfile[0])
     return;
 
-  out = fopen(pidfile, "w");
-  if (!out) {
-    LOG_FATAL("Could not open %s : %s", pidfile, strerror(errno));
-  } else {
-    fprintf(out, "%d\n", (int)getpid());
-    fclose(out);
-  }
+  out = UTI_OpenFile(NULL, pidfile, NULL, 'W', 0644);
+  fprintf(out, "%d\n", (int)getpid());
+  fclose(out);
 }
 
 /* ================================================== */
diff --git a/sysincl.h b/sysincl.h
index 296c5e6..873a3bd 100644
--- a/sysincl.h
+++ b/sysincl.h
@@ -37,6 +37,7 @@
 #include <glob.h>
 #include <grp.h>
 #include <inttypes.h>
+#include <limits.h>
 #include <math.h>
 #include <netinet/in.h>
 #include <pwd.h>
diff --git a/util.c b/util.c
index e7e3442..83b3b20 100644
--- a/util.c
+++ b/util.c
@@ -1179,6 +1179,101 @@ UTI_CheckDirPermissions(const char *path, mode_t perm, uid_t uid, gid_t gid)
 
 /* ================================================== */
 
+static int
+join_path(const char *basedir, const char *name, const char *suffix,
+          char *buffer, size_t length, LOG_Severity severity)
+{
+  const char *sep;
+
+  if (!basedir) {
+    basedir = "";
+    sep = "";
+  } else {
+    sep = "/";
+  }
+
+  if (!suffix)
+    suffix = "";
+
+  if (snprintf(buffer, length, "%s%s%s%s", basedir, sep, name, suffix) >= length) {
+    LOG(severity, "File path %s%s%s%s too long", basedir, sep, name, suffix);
+    return 0;
+  }
+
+  return 1;
+}
+
+/* ================================================== */
+
+FILE *
+UTI_OpenFile(const char *basedir, const char *name, const char *suffix,
+             char mode, mode_t perm)
+{
+  const char *file_mode;
+  char path[PATH_MAX];
+  LOG_Severity severity;
+  int fd, flags;
+  FILE *file;
+
+  severity = mode >= 'A' && mode <= 'Z' ? LOGS_FATAL : LOGS_ERR;
+
+  if (!join_path(basedir, name, suffix, path, sizeof (path), severity))
+    return NULL;
+
+  switch (mode) {
+    case 'r':
+    case 'R':
+      flags = O_RDONLY;
+      file_mode = "r";
+      if (severity != LOGS_FATAL)
+        severity = LOGS_DEBUG;
+      break;
+    case 'w':
+    case 'W':
+      flags = O_WRONLY | O_CREAT | O_EXCL;
+      file_mode = "w";
+      break;
+    case 'a':
+    case 'A':
+      flags = O_WRONLY | O_CREAT | O_APPEND;
+      file_mode = "a";
+      break;
+    default:
+      assert(0);
+      return NULL;
+  }
+
+try_again:
+  fd = open(path, flags, perm);
+  if (fd < 0) {
+    if (errno == EEXIST) {
+      if (unlink(path) < 0) {
+        LOG(severity, "Could not remove %s : %s", path, strerror(errno));
+        return NULL;
+      }
+      DEBUG_LOG("Removed %s", path);
+      goto try_again;
+    }
+    LOG(severity, "Could not open %s : %s", path, strerror(errno));
+    return NULL;
+  }
+
+  UTI_FdSetCloexec(fd);
+
+  file = fdopen(fd, file_mode);
+  if (!file) {
+    LOG(severity, "Could not open %s : %s", path, strerror(errno));
+    close(fd);
+    return NULL;
+  }
+
+  DEBUG_LOG("Opened %s fd=%d mode=%c", path, fd, mode);
+
+  return file;
+}
+
+/* ================================================== */
+
 void
 UTI_DropRoot(uid_t uid, gid_t gid)
 {
diff --git a/util.h b/util.h
index e3d6767..a2481cc 100644
--- a/util.h
+++ b/util.h
@@ -176,6 +176,17 @@ extern int UTI_CreateDirAndParents(const char *path, mode_t mode, uid_t uid, gid
    permissions and its uid/gid must match the specified values. */
 extern int UTI_CheckDirPermissions(const char *path, mode_t perm, uid_t uid, gid_t gid);
 
+/* Open a file.  The full path of the file is constructed from the basedir
+   (may be NULL), '/' (if basedir is not NULL), name, and suffix (may be NULL).
+   Created files have specified permissions (umasked).  Returns NULL on error.
+   The following modes are supported (if the mode is an uppercase character,
+   errors are fatal):
+   r/R - open an existing file for reading
+   w/W - open a new file for writing (remove existing file)
+   a/A - open an existing file for appending (create if does not exist) */
+extern FILE *UTI_OpenFile(const char *basedir, const char *name, const char *suffix,
+                          char mode, mode_t perm);
+
 /* Set process user/group IDs and drop supplementary groups */
 extern void UTI_DropRoot(uid_t uid, gid_t gid);
 
-- 
1.8.3.1