[PATCH] Save/restore CWD more reliably on Unix

[PATCH] Save/restore CWD more reliably on Unix

[Colin Watson]

Various GRUB utilities fail if the current directory doesn't exist,
because grub_find_device chdirs to a different directory and then fails
when trying to chdir back.  Gnulib's save-cwd module uses fchdir instead
when it can, avoiding this category of problem.

Fixes Debian bug #918700.

Signed-off-by: Colin Watson <cjwatson@ubuntu.com>
---
 bootstrap.conf                 |  1 +
 grub-core/osdep/unix/getroot.c | 26 +++++++++++++++++---------
 2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/bootstrap.conf b/bootstrap.conf
index 6781d25a7..988dda099 100644
--- a/bootstrap.conf
+++ b/bootstrap.conf
@@ -33,6 +33,7 @@ gnulib_modules="
   progname
   realloc-gnu
   regex
+  save-cwd
 "
 
 gnulib_tool_option_extras="\
diff --git a/grub-core/osdep/unix/getroot.c b/grub-core/osdep/unix/getroot.c
index 3046e22cc..46d7116c6 100644
--- a/grub-core/osdep/unix/getroot.c
+++ b/grub-core/osdep/unix/getroot.c
@@ -34,6 +34,7 @@
 #ifdef HAVE_LIMITS_H
 #include <limits.h>
 #endif
+
 #include <grub/util/misc.h>
 #include <grub/emu/exec.h>
 
@@ -113,6 +114,8 @@
 #include <sys/mount.h>
 #endif
 
+#include "save-cwd.h"
+
 #if !defined (__GNU__)
 static void
 strip_extra_slashes (char *dir)
@@ -352,7 +355,7 @@ char *
 grub_find_device (const char *dir, dev_t dev)
 {
   DIR *dp;
-  char *saved_cwd;
+  struct saved_cwd saved_cwd;
   struct dirent *ent;
 
   if (! dir)
@@ -362,12 +365,17 @@ grub_find_device (const char *dir, dev_t dev)
   if (! dp)
     return 0;
 
-  saved_cwd = xgetcwd ();
+  if (save_cwd (&saved_cwd) < 0)
+    {
+      grub_util_error ("%s", _("cannot save the original directory"));
+      closedir (dp);
+      return 0;
+    }
 
   grub_util_info ("changing current directory to %s", dir);
   if (chdir (dir) < 0)
     {
-      free (saved_cwd);
+      free_cwd (&saved_cwd);
       closedir (dp);
       return 0;
     }
@@ -410,11 +418,11 @@ grub_find_device (const char *dir, dev_t dev)
 
 	  if (res)
 	    {
-	      if (chdir (saved_cwd) < 0)
+	      if (restore_cwd (&saved_cwd) < 0)
 		grub_util_error ("%s",
 				 _("cannot restore the original directory"));
 
-	      free (saved_cwd);
+	      free_cwd (&saved_cwd);
 	      closedir (dp);
 	      return res;
 	    }
@@ -468,19 +476,19 @@ grub_find_device (const char *dir, dev_t dev)
 	      continue;
 	    }
 
-	  if (chdir (saved_cwd) < 0)
+	  if (restore_cwd (&saved_cwd) < 0)
 	    grub_util_error ("%s", _("cannot restore the original directory"));
 
-	  free (saved_cwd);
+	  free_cwd (&saved_cwd);
 	  closedir (dp);
 	  return res;
 	}
     }
 
-  if (chdir (saved_cwd) < 0)
+  if (restore_cwd (&saved_cwd) < 0)
     grub_util_error ("%s", _("cannot restore the original directory"));
 
-  free (saved_cwd);
+  free_cwd (&saved_cwd);
   closedir (dp);
   return 0;
 }
-- 
2.17.1

Re: [PATCH] Save/restore CWD more reliably on Unix

[Daniel Kiper]

On Sat, Mar 09, 2019 at 02:37:17PM +0000, Colin Watson wrote:
> Various GRUB utilities fail if the current directory doesn't exist,
> because grub_find_device chdirs to a different directory and then fails
> when trying to chdir back.  Gnulib's save-cwd module uses fchdir instead
> when it can, avoiding this category of problem.
>
> Fixes Debian bug #918700.
>
> Signed-off-by: Colin Watson <cjwatson@ubuntu.com>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Daniel