From 5e7a3c2e7e118c7f12d5dfda9f9140f638976aa2 Mon Sep 17 00:00:00 2001
From: Benno Schulenberg <bensberg@telfort.nl>
Date: Sun, 28 Apr 2024 10:51:52 +0200
Subject: 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.

Cherry-picked-by: Lukáš Zaoral <lzaoral@redhat.com>
Upstream-commit: 5e7a3c2e7e118c7f12d5dfda9f9140f638976aa2

diff --git a/src/definitions.h b/src/definitions.h
index af3a793..55d8235 100644
--- a/src/definitions.h
+++ b/src/definitions.h
@@ -254,7 +254,7 @@ typedef enum {
 } message_type;
 
 typedef enum {
-	OVERWRITE, APPEND, PREPEND
+	OVERWRITE, APPEND, PREPEND, EMERGENCY
 } kind_of_writing_type;
 
 typedef enum {
diff --git a/src/files.c b/src/files.c
index 57c2001..584b579 100644
--- a/src/files.c
+++ b/src/files.c
@@ -1751,6 +1751,8 @@ 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;
@@ -1830,7 +1830,6 @@ 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 = (tmp ? S_IRUSR|S_IWUSR : RW_FOR_ALL);
-		int fd;
 
 #ifndef NANO_TINY
 		block_sigwinch(TRUE);
@@ -1953,6 +1953,16 @@ bool write_file(const char *name, FILE *thefile, bool normal,
 		goto cleanup_and_exit;
 	}
 
+#ifndef NANO_TINY
+	/* 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));
 		goto cleanup_and_exit;
 
diff --git a/src/nano.c b/src/nano.c
index 90b4a0b..973054f 100644
--- a/src/nano.c
+++ b/src/nano.c
@@ -321,25 +321,15 @@ void emergency_save(const char *filename)
 	targetname = get_next_filename(plainname, ".save");
 
 	if (*targetname != '\0')
-		failed = !write_file(targetname, NULL, TRUE, OVERWRITE, FALSE);
+		failed = !write_file(targetname, NULL, TRUE, EMERGENCY, FALSE);
 
 	if (!failed)
 		fprintf(stderr, _("\nBuffer written to %s\n"), targetname);
 	else if (*targetname != '\0')
 		fprintf(stderr, _("\nBuffer not written to %s: %s\n"),
 										targetname, strerror(errno));
 	else
 		fprintf(stderr, _("\nToo many .save files"));
-
-#ifndef NANO_TINY
-	/* 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);
 }
-- 
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