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files: run `chmod` and `chown` on the descriptor, not on the filename 

This closes a window of opportunity where the emergency file could be
replaced by a malicious symlink.

The issue was reported by `MartinJM` and `InvisibleMeerkat`.

Problem existed since version 2.2.0, commit 123110c5, when chmodding
and chowning of the emergency .save file was added.
This commit is contained in:
Benno Schulenberg 2024-04-28 10:51:52 +02:00
parent 24393c6563
commit ffc74e5067
3 changed files with 14 additions and 13 deletions
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2
src/definitions.h
View File

@ -283,7 +283,7 @@ typedef enum {
} message_type;
typedef enum {
OVERWRITE, APPEND, PREPEND
OVERWRITE, APPEND, PREPEND, EMERGENCY
} kind_of_writing_type;
typedef enum {

13
src/files.c
View File

@ -1760,6 +1760,8 @@ bool write_file(const char *name, FILE *thefile, bool normal,
#endif
char *realname = real_dir_from_tilde(name);
/* The filename after tilde expansion. */
int fd = 0;
/* The descriptor that is assigned when opening the file. */
char *tempname = NULL;
/* The name of the temporary file we use when prepending. */
linestruct *line = openfile->filetop;
@ -1843,7 +1845,6 @@ bool write_file(const char *name, FILE *thefile, bool normal,
* For an emergency file, access is restricted to just the owner. */
if (thefile == NULL) {
mode_t permissions = (normal ? RW_FOR_ALL : S_IRUSR|S_IWUSR);
int fd;
#ifndef NANO_TINY
block_sigwinch(TRUE);
@ -1969,6 +1970,16 @@ bool write_file(const char *name, FILE *thefile, bool normal,
}
#endif
#if !defined(NANO_TINY) && defined(HAVE_CHMOD) && defined(HAVE_CHOWN)
/* Change permissions and owner of an emergency save file to the values
* of the original file, but ignore any failure as we are in a hurry. */
if (method == EMERGENCY && fd && openfile->statinfo) {
IGNORE_CALL_RESULT(fchmod(fd, openfile->statinfo->st_mode));
IGNORE_CALL_RESULT(fchown(fd, openfile->statinfo->st_uid,
openfile->statinfo->st_gid));
}
#endif
if (fclose(thefile) != 0) {
statusline(ALERT, _("Error writing %s: %s"), realname, strerror(errno));

12
src/nano.c
View File

@ -337,18 +337,8 @@ void emergency_save(const char *filename)
if (*targetname == '\0')
fprintf(stderr, _("\nToo many .save files\n"));
else if (write_file(targetname, NULL, SPECIAL, OVERWRITE, NONOTES)) {
else if (write_file(targetname, NULL, SPECIAL, EMERGENCY, NONOTES))
fprintf(stderr, _("\nBuffer written to %s\n"), targetname);
#if !defined(NANO_TINY) && defined(HAVE_CHMOD) && defined(HAVE_CHOWN)
/* Try to chmod/chown the saved file to the values of the original file,
* but ignore any failure as we are in a hurry to get out. */
if (openfile->statinfo) {
IGNORE_CALL_RESULT(chmod(targetname, openfile->statinfo->st_mode));
IGNORE_CALL_RESULT(chown(targetname, openfile->statinfo->st_uid,
openfile->statinfo->st_gid));
}
#endif
}
free(targetname);
free(plainname);