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Close a race when statting and reading files.

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* fileio.c (Finsert_file_contents): Use open+fstat, not stat+open.
This avoids a race if the file is renamed between stat and open.
This race is not the problem originally noted in Bug#13149;
see <http://bugs.gnu.org/13149#73> and later messages in the thread.
This commit is contained in:
Paul Eggert 2013-01-17 21:12:08 -08:00
parent 0eb8768885
commit 6772211202
2 changed files with 21 additions and 31 deletions
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8
src/ChangeLog
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@ -1,3 +1,11 @@
2013-01-17 Paul Eggert <eggert@cs.ucla.edu>
Close a race when statting and reading files (Bug#13149).
* fileio.c (Finsert_file_contents): Use open+fstat, not stat+open.
This avoids a race if the file is renamed between stat and open.
This race is not the problem originally noted in Bug#13149;
see <http://bugs.gnu.org/13149#73> and later messages in the thread.
2013-01-17 Dmitry Antipov <dmantipov@yandex.ru>
* lisp.h (toplevel): Add comment about using Lisp_Save_Value

44
src/fileio.c
View file

@ -3492,7 +3492,6 @@ by calling `format-decode', which see. */)
(Lisp_Object filename, Lisp_Object visit, Lisp_Object beg, Lisp_Object end, Lisp_Object replace)
{
struct stat st;
int file_status;
EMACS_TIME mtime;
int fd;
ptrdiff_t inserted = 0;
@ -3554,26 +3553,9 @@ by calling `format-decode', which see. */)
orig_filename = filename;
filename = ENCODE_FILE (filename);
fd = -1;
#ifdef WINDOWSNT
{
Lisp_Object tem = Vw32_get_true_file_attributes;
/* Tell stat to use expensive method to get accurate info. */
Vw32_get_true_file_attributes = Qt;
file_status = stat (SSDATA (filename), &st);
Vw32_get_true_file_attributes = tem;
}
#else
file_status = stat (SSDATA (filename), &st);
#endif /* WINDOWSNT */
if (file_status == 0)
mtime = get_stat_mtime (&st);
else
fd = emacs_open (SSDATA (filename), O_RDONLY, 0);
if (fd < 0)
{
badopen:
save_errno = errno;
if (NILP (visit))
report_file_error ("Opening input file", Fcons (orig_filename, Qnil));
@ -3585,6 +3567,17 @@ by calling `format-decode', which see. */)
goto notfound;
}
/* Replacement should preserve point as it preserves markers. */
if (!NILP (replace))
record_unwind_protect (restore_point_unwind, Fpoint_marker ());
record_unwind_protect (close_file_unwind, make_number (fd));
if (fstat (fd, &st) != 0)
report_file_error ("Getting input file status",
Fcons (orig_filename, Qnil));
mtime = get_stat_mtime (&st);
/* This code will need to be changed in order to work on named
pipes, and it's probably just not worth it. So we should at
least signal an error. */
@ -3600,17 +3593,6 @@ by calling `format-decode', which see. */)
build_string ("not a regular file"), orig_filename);
}
if (fd < 0)
if ((fd = emacs_open (SSDATA (filename), O_RDONLY, 0)) < 0)
goto badopen;
/* Replacement should preserve point as it preserves markers. */
if (!NILP (replace))
record_unwind_protect (restore_point_unwind, Fpoint_marker ());
record_unwind_protect (close_file_unwind, make_number (fd));
if (!NILP (visit))
{
if (!NILP (beg) || !NILP (end))