From b3ad638a60845f17938ff812efcf2b2edfbd8c57 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Mon, 20 Jan 2020 01:08:42 -0800
Subject: [PATCH] Work better if stat etc. are interrupted

Quit or retry if fstat, lstat, stat or openat fail with EINTR.
This should fix some bugs on platforms where accessing files via
NFS can fail that way (Bug#9256).
* src/dired.c (file_attributes):
* src/fileio.c (file_directory_p) [O_PATH]:
Use emacs_openat instead of openat.
* src/dired.c (file_attributes): Use emacs_fstatat instead of fstatat.
* src/fileio.c (barf_or_query_if_file_exists, Frename_file):
* src/filelock.c (rename_lock_file):
Use emacs_fstatat instead of lstat.
* src/fileio.c (file_directory_p, Ffile_regular_p, Ffile_modes)
(Ffile_newer_than_file_p, Fverify_visited_file_modtime)
(Fset_visited_file_modtime, auto_save_1):
* src/lread.c (Fload):
* src/sysdep.c (get_current_dir_name_or_unreachable):
Use emacs_fstatat instead of stat.
* src/sysdep.c (emacs_fstatat, emacs_openat): New functions.
(emacs_open): Redo in terms of emacs_open.
---
 src/dired.c    |  4 ++--
 src/fileio.c   | 39 ++++++++++++++++++++++++---------------
 src/filelock.c |  3 ++-
 src/lisp.h     |  2 ++
 src/lread.c    |  4 ++--
 src/sysdep.c   | 36 +++++++++++++++++++++++++++++++-----
 6 files changed, 63 insertions(+), 25 deletions(-)

diff --git src/dired.c src/dired.c
index 611477aa4e..f013a4cea0 100644
--- src/dired.c
+++ src/dired.c
@@ -937,7 +937,7 @@ file_attributes (int fd, char const *name,
   int err = EINVAL;
 
 #if defined O_PATH && !defined HAVE_CYGWIN_O_PATH_BUG
-  int namefd = openat (fd, name, O_PATH | O_CLOEXEC | O_NOFOLLOW);
+  int namefd = emacs_openat (fd, name, O_PATH | O_CLOEXEC | O_NOFOLLOW, 0);
   if (namefd < 0)
     err = errno;
   else
@@ -970,7 +970,7 @@ file_attributes (int fd, char const *name,
 	 information to be accurate.  */
       w32_stat_get_owner_group = 1;
 #endif
-      err = fstatat (fd, name, &s, AT_SYMLINK_NOFOLLOW) == 0 ? 0 : errno;
+      err = emacs_fstatat (fd, name, &s, AT_SYMLINK_NOFOLLOW) == 0 ? 0 : errno;
 #ifdef WINDOWSNT
       w32_stat_get_owner_group = 0;
 #endif
diff --git src/fileio.c src/fileio.c
index 34934dd6df..87a17eab42 100644
--- src/fileio.c
+++ src/fileio.c
@@ -1952,7 +1952,10 @@ barf_or_query_if_file_exists (Lisp_Object absname, bool known_to_exist,
 
   encoded_filename = ENCODE_FILE (absname);
 
-  if (! known_to_exist && lstat (SSDATA (encoded_filename), &statbuf) == 0)
+  if (! known_to_exist
+      && (emacs_fstatat (AT_FDCWD, SSDATA (encoded_filename),
+			 &statbuf, AT_SYMLINK_NOFOLLOW)
+	  == 0))
     {
       if (S_ISDIR (statbuf.st_mode))
 	xsignal2 (Qfile_error,
@@ -2555,7 +2558,9 @@ DEFUN ("rename-file", Frename_file, Srename_file, 2, 3,
   bool dirp = !NILP (Fdirectory_name_p (file));
   if (!dirp)
     {
-      if (lstat (SSDATA (encoded_file), &file_st) != 0)
+      if (emacs_fstatat (AT_FDCWD, SSDATA (encoded_file),
+			 &file_st, AT_SYMLINK_NOFOLLOW)
+	  != 0)
 	report_file_error ("Renaming", list2 (file, newname));
       dirp = S_ISDIR (file_st.st_mode) != 0;
     }
@@ -2928,7 +2933,8 @@ file_directory_p (Lisp_Object file)
 #else
 # ifdef O_PATH
   /* Use O_PATH if available, as it avoids races and EOVERFLOW issues.  */
-  int fd = openat (AT_FDCWD, SSDATA (file), O_PATH | O_CLOEXEC | O_DIRECTORY);
+  int fd = emacs_openat (AT_FDCWD, SSDATA (file),
+			 O_PATH | O_CLOEXEC | O_DIRECTORY, 0);
   if (0 <= fd)
     {
       emacs_close (fd);
@@ -2939,9 +2945,9 @@ file_directory_p (Lisp_Object file)
   /* O_PATH is defined but evidently this Linux kernel predates 2.6.39.
      Fall back on generic POSIX code.  */
 # endif
-  /* Use file_accessible_directory_p, as it avoids stat EOVERFLOW
+  /* Use file_accessible_directory_p, as it avoids fstatat EOVERFLOW
      problems and could be cheaper.  However, if it fails because FILE
-     is inaccessible, fall back on stat; if the latter fails with
+     is inaccessible, fall back on fstatat; if the latter fails with
      EOVERFLOW then FILE must have been a directory unless a race
      condition occurred (a problem hard to work around portably).  */
   if (file_accessible_directory_p (file))
@@ -2949,7 +2955,7 @@ file_directory_p (Lisp_Object file)
   if (errno != EACCES)
     return false;
   struct stat st;
-  if (stat (SSDATA (file), &st) != 0)
+  if (emacs_fstatat (AT_FDCWD, SSDATA (file), &st, 0) != 0)
     return errno == EOVERFLOW;
   if (S_ISDIR (st.st_mode))
     return true;
@@ -3080,7 +3086,7 @@ DEFUN ("file-regular-p", Ffile_regular_p, Sfile_regular_p, 1, 1, 0,
   Vw32_get_true_file_attributes = Qt;
 #endif
 
-  int stat_result = stat (SSDATA (absname), &st);
+  int stat_result = emacs_fstatat (AT_FDCWD, SSDATA (absname), &st, 0);
 
 #ifdef WINDOWSNT
   Vw32_get_true_file_attributes = true_attributes;
@@ -3340,7 +3346,7 @@ DEFUN ("file-modes", Ffile_modes, Sfile_modes, 1, 1, 0,
   if (!NILP (handler))
     return call2 (handler, Qfile_modes, absname);
 
-  if (stat (SSDATA (ENCODE_FILE (absname)), &st) != 0)
+  if (emacs_fstatat (AT_FDCWD, SSDATA (ENCODE_FILE (absname)), &st, 0) != 0)
     return file_attribute_errno (absname, errno);
   return make_fixnum (st.st_mode & 07777);
 }
@@ -3486,7 +3492,7 @@ DEFUN ("file-newer-than-file-p", Ffile_newer_than_file_p, Sfile_newer_than_file_
     return call3 (handler, Qfile_newer_than_file_p, absname1, absname2);
 
   int err1;
-  if (stat (SSDATA (ENCODE_FILE (absname1)), &st1) == 0)
+  if (emacs_fstatat (AT_FDCWD, SSDATA (ENCODE_FILE (absname1)), &st1, 0) == 0)
     err1 = 0;
   else
     {
@@ -3494,7 +3500,7 @@ DEFUN ("file-newer-than-file-p", Ffile_newer_than_file_p, Sfile_newer_than_file_
       if (err1 != EOVERFLOW)
 	return file_attribute_errno (absname1, err1);
     }
-  if (stat (SSDATA (ENCODE_FILE (absname2)), &st2) != 0)
+  if (emacs_fstatat (AT_FDCWD, SSDATA (ENCODE_FILE (absname2)), &st2, 0) != 0)
     {
       file_attribute_errno (absname2, errno);
       return Qt;
@@ -3880,7 +3886,7 @@ because (1) it preserves some marker positions and (2) it puts less data
 	  if (end_offset < 0)
 	    buffer_overflow ();
 
-	  /* The file size returned from stat may be zero, but data
+	  /* The file size returned from fstat may be zero, but data
 	     may be readable nonetheless, for example when this is a
 	     file in the /proc filesystem.  */
 	  if (end_offset == 0)
@@ -5625,7 +5631,7 @@ DEFUN ("verify-visited-file-modtime", Fverify_visited_file_modtime,
 
   filename = ENCODE_FILE (BVAR (b, filename));
 
-  mtime = (stat (SSDATA (filename), &st) == 0
+  mtime = (emacs_fstatat (AT_FDCWD, SSDATA (filename), &st, 0) == 0
 	   ? get_stat_mtime (&st)
 	   : time_error_value (errno));
   if (timespec_cmp (mtime, b->modtime) == 0
@@ -5689,7 +5695,8 @@ DEFUN ("set-visited-file-modtime", Fset_visited_file_modtime,
 	/* The handler can find the file name the same way we did.  */
 	return call2 (handler, Qset_visited_file_modtime, Qnil);
 
-      if (stat (SSDATA (ENCODE_FILE (filename)), &st) == 0)
+      if (emacs_fstatat (AT_FDCWD, SSDATA (ENCODE_FILE (filename)), &st, 0)
+	  == 0)
         {
 	  current_buffer->modtime = get_stat_mtime (&st);
           current_buffer->modtime_size = st.st_size;
@@ -5728,12 +5735,14 @@ auto_save_1 (void)
   /* Get visited file's mode to become the auto save file's mode.  */
   if (! NILP (BVAR (current_buffer, filename)))
     {
-      if (stat (SSDATA (BVAR (current_buffer, filename)), &st) >= 0)
+      if (emacs_fstatat (AT_FDCWD, SSDATA (BVAR (current_buffer, filename)),
+			 &st, 0)
+	  == 0)
 	/* But make sure we can overwrite it later!  */
 	auto_save_mode_bits = (st.st_mode | 0600) & 0777;
       else if (modes = Ffile_modes (BVAR (current_buffer, filename)),
 	       FIXNUMP (modes))
-	/* Remote files don't cooperate with stat.  */
+	/* Remote files don't cooperate with fstatat.  */
 	auto_save_mode_bits = (XFIXNUM (modes) | 0600) & 0777;
     }
 
diff --git src/filelock.c src/filelock.c
index b28f16e9b5..73202f0b2c 100644
--- src/filelock.c
+++ src/filelock.c
@@ -347,7 +347,8 @@ rename_lock_file (char const *old, char const *new, bool force)
 	 potential race condition since some other process may create
 	 NEW immediately after the existence check, but it's the best
 	 we can portably do here.  */
-      if (lstat (new, &st) == 0 || errno == EOVERFLOW)
+      if (emacs_fstatat (AT_FDCWD, new, &st, AT_SYMLINK_NOFOLLOW) == 0
+	  || errno == EOVERFLOW)
 	{
 	  errno = EEXIST;
 	  return -1;
diff --git src/lisp.h src/lisp.h
index 4bcd122844..0bd375658e 100644
--- src/lisp.h
+++ src/lisp.h
@@ -4605,6 +4605,8 @@ maybe_disable_address_randomization (int argc, char **argv)
 extern void init_random (void);
 extern void emacs_backtrace (int);
 extern AVOID emacs_abort (void) NO_INLINE;
+extern int emacs_fstatat (int, char const *, void *, int);
+extern int emacs_openat (int, char const *, int, int);
 extern int emacs_open (const char *, int, int);
 extern int emacs_pipe (int[2]);
 extern int emacs_close (int);
diff --git src/lread.c src/lread.c
index 4e9860d5dc..69dd73912b 100644
--- src/lread.c
+++ src/lread.c
@@ -1353,11 +1353,11 @@ DEFUN ("load", Fload, Sload, 1, 5, 0,
              ignores suffix order due to load_prefer_newer.  */
           if (!load_prefer_newer && is_elc)
             {
-              result = stat (SSDATA (efound), &s1);
+	      result = emacs_fstatat (AT_FDCWD, SSDATA (efound), &s1, 0);
               if (result == 0)
                 {
                   SSET (efound, SBYTES (efound) - 1, 0);
-                  result = stat (SSDATA (efound), &s2);
+		  result = emacs_fstatat (AT_FDCWD, SSDATA (efound), &s2, 0);
                   SSET (efound, SBYTES (efound) - 1, 'c');
                 }
 
diff --git src/sysdep.c src/sysdep.c
index c6344d8cec..e8e8bbfb50 100644
--- src/sysdep.c
+++ src/sysdep.c
@@ -312,8 +312,8 @@ get_current_dir_name_or_unreachable (void)
   if (pwd
       && (pwdlen = strnlen (pwd, bufsize_max)) < bufsize_max
       && IS_DIRECTORY_SEP (pwd[pwdlen && IS_DEVICE_SEP (pwd[1]) ? 2 : 0])
-      && stat (pwd, &pwdstat) == 0
-      && stat (".", &dotstat) == 0
+      && emacs_fstatat (AT_FDCWD, pwd, &pwdstat, 0) == 0
+      && emacs_fstatat (AT_FDCWD, ".", &dotstat, 0) == 0
       && dotstat.st_ino == pwdstat.st_ino
       && dotstat.st_dev == pwdstat.st_dev)
     {
@@ -2449,7 +2449,27 @@ emacs_abort (void)
 }
 #endif
 
-/* Open FILE for Emacs use, using open flags OFLAG and mode MODE.
+/* Assuming the directory DIRFD, store information about FILENAME into *ST,
+   using FLAGS to control how the status is obtained.
+   Do not fail merely because fetching info was interrupted by a signal.
+   Allow the user to quit.
+
+   The type of ST is void * instead of struct stat * because the
+   latter type would be problematic in lisp.h.  Some platforms may
+   play tricks like "#define stat stat64" in <sys/stat.h>, and lisp.h
+   does not include <sys/stat.h>.  */
+
+int
+emacs_fstatat (int dirfd, char const *filename, void *st, int flags)
+{
+  int r;
+  while ((r = fstatat (dirfd, filename, st, flags)) != 0 && errno == EINTR)
+    maybe_quit ();
+  return r;
+}
+
+/* Assuming the directory DIRFD, open FILE for Emacs use,
+   using open flags OFLAGS and mode MODE.
    Use binary I/O on systems that care about text vs binary I/O.
    Arrange for subprograms to not inherit the file descriptor.
    Prefer a method that is multithread-safe, if available.
@@ -2457,17 +2477,23 @@ emacs_abort (void)
    Allow the user to quit.  */
 
 int
-emacs_open (const char *file, int oflags, int mode)
+emacs_openat (int dirfd, char const *file, int oflags, int mode)
 {
   int fd;
   if (! (oflags & O_TEXT))
     oflags |= O_BINARY;
   oflags |= O_CLOEXEC;
-  while ((fd = open (file, oflags, mode)) < 0 && errno == EINTR)
+  while ((fd = openat (dirfd, file, oflags, mode)) < 0 && errno == EINTR)
     maybe_quit ();
   return fd;
 }
 
+int
+emacs_open (char const *file, int oflags, int mode)
+{
+  return emacs_openat (AT_FDCWD, file, oflags, mode);
+}
+
 /* Open FILE as a stream for Emacs use, with mode MODE.
    Act like emacs_open with respect to threads, signals, and quits.  */
 
-- 
2.37.1

