From: Karel Zak <kzak@redhat.com>
Date: Mon, 25 Oct 2010 10:26:28 +0000 (+0200)
Subject: umount: umount -r segfault
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=973d9cf9c6092d94a3e5b54e5b8e7cd4e2d705d7;p=util-linux

umount: umount -r segfault

umount(8) segfaults when update incomplete mtab file after remount to
read-only (-r). For example autofs does not store info about
mountpoint to /etc/mtab file.

	# mount /dev/sda1 /mnt/test
	# sed -i -e 's:/dev/sda1 .*::g' /etc/mtab
	# cd /mnt/test
	# umount -r /mnt/test
	umount: /mnt/test busy - remounted read-only
	Segmentation fault

The command "umount -r" should not care about /etc/mtab if the related
mtab entry does not exist.

Reported-by: Paul Crawford <psc@sat.dundee.ac.uk>
Addresses: https://bugs.launchpad.net/bugs/579858
Signed-off-by: Karel Zak <kzak@redhat.com>
---

diff --git a/mount/umount.c b/mount/umount.c
index 49741a51..b5ff8a17 100644
--- a/mount/umount.c
+++ b/mount/umount.c
@@ -267,15 +267,20 @@ umount_one (const char *spec, const char *node, const char *type,
 		res = mount(spec, node, NULL,
 			    MS_MGC_VAL | MS_REMOUNT | MS_RDONLY, NULL);
 		if (res == 0) {
-			struct my_mntent remnt;
 			fprintf(stderr,
 				_("umount: %s busy - remounted read-only\n"),
 				spec);
-			remnt.mnt_type = remnt.mnt_fsname = NULL;
-			remnt.mnt_dir = xstrdup(node);
-			remnt.mnt_opts = xstrdup("ro");
-			if (!nomtab)
+			if (mc && !nomtab) {
+				/* update mtab if the entry is there */
+				struct my_mntent remnt;
+				remnt.mnt_fsname = mc->m.mnt_fsname;
+				remnt.mnt_dir = mc->m.mnt_dir;
+				remnt.mnt_type = mc->m.mnt_type;
+				remnt.mnt_opts = "ro";
+				remnt.mnt_freq = 0;
+				remnt.mnt_passno = 0;
 				update_mtab(node, &remnt);
+			}
 			return 0;
 		} else if (errno != EBUSY) { 	/* hmm ... */
 			perror("remount");