commit dce4683cbbe107a95f1f0d45fabc304acfb5d71a

Author: Andreas Gruenbacher <agruen@gnu.org>

Date:   Mon Jul 15 16:21:48 2019 +0200

    Don't follow symlinks unless --follow-symlinks is given

    * src/inp.c (plan_a, plan_b), src/util.c (copy_to_fd, copy_file,

    append_to_file): Unless the --follow-symlinks option is given, open files with

    the O_NOFOLLOW flag to avoid following symlinks.  So far, we were only doing

    that consistently for input files.

    * src/util.c (create_backup): When creating empty backup files, (re)create them

    with O_CREAT | O_EXCL to avoid following symlinks in that case as well.

diff --git a/src/inp.c b/src/inp.c

index 32d0919..22d7473 100644

--- a/src/inp.c

+++ b/src/inp.c

@@ -238,8 +238,13 @@ plan_a (char const *filename)

     {

       if (S_ISREG (instat.st_mode))

         {

-	  int ifd = safe_open (filename, O_RDONLY|binary_transput, 0);

+	  int flags = O_RDONLY | binary_transput;

 	  size_t buffered = 0, n;

+	  int ifd;

+

+	  if (! follow_symlinks)

+	    flags |= O_NOFOLLOW;

+	  ifd = safe_open (filename, flags, 0);

 	  if (ifd < 0)

 	    pfatal ("can't open file %s", quotearg (filename));

@@ -340,6 +345,7 @@ plan_a (char const *filename)

 static void

 plan_b (char const *filename)

 {

+  int flags = O_RDONLY | binary_transput;

   int ifd;

   FILE *ifp;

   int c;

@@ -353,7 +359,9 @@ plan_b (char const *filename)

   if (instat.st_size == 0)

     filename = NULL_DEVICE;

-  if ((ifd = safe_open (filename, O_RDONLY | binary_transput, 0)) < 0

+  if (! follow_symlinks)

+    flags |= O_NOFOLLOW;

+  if ((ifd = safe_open (filename, flags, 0)) < 0

       || ! (ifp = fdopen (ifd, binary_transput ? "rb" : "r")))

     pfatal ("Can't open file %s", quotearg (filename));

   if (TMPINNAME_needs_removal)

diff --git a/src/util.c b/src/util.c

index 1cc08ba..fb38307 100644

--- a/src/util.c

+++ b/src/util.c

@@ -388,7 +388,7 @@ create_backup (char const *to, const struct stat *to_st, bool leave_original)

 	  try_makedirs_errno = ENOENT;

 	  safe_unlink (bakname);

-	  while ((fd = safe_open (bakname, O_CREAT | O_WRONLY | O_TRUNC, 0666)) < 0)

+	  while ((fd = safe_open (bakname, O_CREAT | O_EXCL | O_WRONLY | O_TRUNC, 0666)) < 0)

 	    {

 	      if (errno != try_makedirs_errno)

 		pfatal ("Can't create file %s", quotearg (bakname));

@@ -579,10 +579,13 @@ create_file (char const *file, int open_flags, mode_t mode,

 static void

 copy_to_fd (const char *from, int tofd)

 {

+  int from_flags = O_RDONLY | O_BINARY;

   int fromfd;

   ssize_t i;

-  if ((fromfd = safe_open (from, O_RDONLY | O_BINARY, 0)) < 0)

+  if (! follow_symlinks)

+    from_flags |= O_NOFOLLOW;

+  if ((fromfd = safe_open (from, from_flags, 0)) < 0)

     pfatal ("Can't reopen file %s", quotearg (from));

   while ((i = read (fromfd, buf, bufsize)) != 0)

     {

@@ -625,6 +628,8 @@ copy_file (char const *from, char const *to, struct stat *tost,

   else

     {

       assert (S_ISREG (mode));

+      if (! follow_symlinks)

+	to_flags |= O_NOFOLLOW;

       tofd = create_file (to, O_WRONLY | O_BINARY | to_flags, mode,

 			  to_dir_known_to_exist);

       copy_to_fd (from, tofd);

@@ -640,9 +645,12 @@ copy_file (char const *from, char const *to, struct stat *tost,

 void

 append_to_file (char const *from, char const *to)

 {

+  int to_flags = O_WRONLY | O_APPEND | O_BINARY;

   int tofd;

-  if ((tofd = safe_open (to, O_WRONLY | O_BINARY | O_APPEND, 0)) < 0)

+  if (! follow_symlinks)

+    to_flags |= O_NOFOLLOW;

+  if ((tofd = safe_open (to, to_flags, 0)) < 0)

     pfatal ("Can't reopen file %s", quotearg (to));

   copy_to_fd (from, tofd);

   if (close (tofd) != 0)