[Nano-devel] [PATCH] pull in the futimens module from gnulib

[Kamil Dudka]

... and use futimens() instead of utime() to prevent a symlink attack
while creating a backup file.  Otherwise, a non-privileged user could
create an arbitrary symlink with name of the backup file and this way
fool a privileged user to call utime() on the attacker-chosen file.
---
 autogen.sh  |  1 +
 src/files.c | 28 ++++++++++++++--------------
 2 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/autogen.sh b/autogen.sh
index 617705c..de9f3bb 100755
--- a/autogen.sh
+++ b/autogen.sh
@@ -5,6 +5,7 @@ gnulib_url="git://git.sv.gnu.org/gnulib.git"
 gnulib_hash="4084b3a1094372b960ce4a97634e08f4538c8bdd"
 
 modules="
+       futimens
        getdelim
        getline
        getopt-gnu
diff --git a/src/files.c b/src/files.c
index 033b963..644b8a1 100644
--- a/src/files.c
+++ b/src/files.c
@@ -1655,13 +1655,13 @@ bool write_file(const char *name, FILE *f_open, bool 
tmp,
        int backup_fd;
        FILE *backup_file;
        char *backupname;
-       struct utimbuf filetime;
+       static struct timespec filetime[2];
        int copy_status;
        int backup_cflags;
 
        /* Save the original file's access and modification times. */
-       filetime.actime = openfile->current_stat->st_atime;
-       filetime.modtime = openfile->current_stat->st_mtime;
+       filetime[/* atime */ 0].tv_sec = openfile->current_stat->st_atime;
+       filetime[/* mtime */ 1].tv_sec = openfile->current_stat->st_mtime;
 
        if (f_open == NULL) {
            /* Open the original file to copy to the backup. */
@@ -1789,17 +1789,8 @@ bool write_file(const char *name, FILE *f_open, bool tmp,
        fprintf(stderr, "Backing up %s to %s\n", realname, backupname);
 #endif
 
-       /* Copy the file. */
-       copy_status = copy_file(f, backup_file);
-
-       if (copy_status != 0) {
-           statusline(ALERT, _("Error reading %s: %s"), realname,
-                       strerror(errno));
-           goto cleanup_and_exit;
-       }
-
-       /* And set its metadata. */
-       if (utime(backupname, &filetime) == -1 && !ISSET(INSECURE_BACKUP)) {
+       /* Set backup's file metadata. */
+       if (futimens(backup_fd, filetime) == -1 && !ISSET(INSECURE_BACKUP)) {
            if (prompt_failed_backupwrite(backupname))
                goto skip_backup;
            statusline(HUSH, _("Error writing backup file %s: %s"),
@@ -1811,6 +1802,15 @@ bool write_file(const char *name, FILE *f_open, bool tmp,
            goto cleanup_and_exit;
        }
 
+       /* Copy the file. */
+       copy_status = copy_file(f, backup_file);
+
+       if (copy_status != 0) {
+           statusline(ALERT, _("Error reading %s: %s"), realname,
+                       strerror(errno));
+           goto cleanup_and_exit;
+       }
+
        free(backupname);
     }
 
-- 
2.9.3