mount.cifs: Properly update mtab during remount

During a remount of a cifs filesystem, the mtab file is not properly
updated, which leads to a doubled entry of the same filesystem in the
/etc/mtab file.  This patch adds a new function del_mtab() which is
called before the add_mtab() in case the fs is being remounted.

The del_mtab() function will delete from the mtab, the old entry from
the filesystem which is being remounted, and then, calls add_mtab() to
add an updated entry to the mtab file.

Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>

1 files changed, 98 insertions, 1 deletions

diff --git a/mount.cifs.c b/mount.cifs.c
index 147f7fc..af071c1 100644
--- a/mount.cifs.c
+++ b/mount.cifs.c
@@ -42,6 +42,7 @@
 #include <fcntl.h>
 #include <limits.h>
 #include <paths.h>
+#include <libgen.h>
 #include <sys/mman.h>
 #include <sys/wait.h>
 #ifdef HAVE_LIBCAP_NG
@@ -161,6 +162,7 @@
 #define OPT_BKUPUID    30
 #define OPT_BKUPGID    31
 
+#define MNT_TMP_FILE "/.mtab.cifs.XXXXXX"
 
 /* struct for holding parsed mount info for use by privleged process */
 struct parsed_mount_info {
@@ -1624,6 +1626,94 @@ add_mtab_exit:
 	return rc;
 }
 
+static int
+del_mtab(char *mountpoint)
+{
+	int tmprc, rc = 0;
+	FILE *mnttmp, *mntmtab;
+	struct mntent *mountent;
+	char *mtabfile, *mtabdir, *mtabtmpfile;
+
+	mtabfile = strdup(MOUNTED);
+	mtabdir = dirname(mtabfile);
+	mtabdir = realloc(mtabdir, strlen(mtabdir) + strlen(MNT_TMP_FILE) + 2);
+	if (!mtabdir) {
+		fprintf(stderr, "del_mtab: cannot determine current mtab path");
+		rc = EX_FILEIO;
+		goto del_mtab_exit;
+	}
+
+	mtabtmpfile = strcat(mtabdir, MNT_TMP_FILE);
+	if (!mtabtmpfile) {
+		fprintf(stderr, "del_mtab: cannot allocate memory to tmp file");
+		rc = EX_FILEIO;
+		goto del_mtab_exit;
+	}
+
+	atexit(unlock_mtab);
+	rc = lock_mtab();
+	if (rc) {
+		fprintf(stderr, "del_mtab: cannot lock mtab");
+		rc = EX_FILEIO;
+		goto del_mtab_exit;
+	}
+
+	mtabtmpfile = mktemp(mtabtmpfile);
+	if (!mtabtmpfile) {
+		fprintf(stderr, "del_mtab: cannot setup tmp file destination");
+		rc = EX_FILEIO;
+		goto del_mtab_exit;
+	}
+
+	mntmtab = setmntent(MOUNTED, "r");
+	if (!mntmtab) {
+		fprintf(stderr, "del_mtab: could not update mount table\n");
+		rc = EX_FILEIO;
+		goto del_mtab_exit;
+	}
+
+	mnttmp = setmntent(mtabtmpfile, "w");
+	if (!mnttmp) {
+		fprintf(stderr, "del_mtab: could not update mount table\n");
+		endmntent(mntmtab);
+		rc = EX_FILEIO;
+		goto del_mtab_exit;
+	}
+
+	while ((mountent = getmntent(mntmtab)) != NULL) {
+		if (!strcmp(mountent->mnt_dir, mountpoint))
+			continue;
+		rc = addmntent(mnttmp, mountent);
+		if (rc) {
+			fprintf(stderr, "del_mtab: unable to add mount entry to mtab\n");
+			rc = EX_FILEIO;
+			goto del_mtab_error;
+		}
+	}
+
+	endmntent(mntmtab);
+
+	tmprc = my_endmntent(mnttmp, 0);
+	if (tmprc) {
+		fprintf(stderr, "del_mtab: error %d detected on close of tmp file\n", tmprc);
+		rc = EX_FILEIO;
+		goto del_mtab_error;
+	}
+
+	rename(mtabtmpfile, MOUNTED);
+
+del_mtab_exit:
+	unlock_mtab();
+	free(mtabdir);
+	return rc;
+
+del_mtab_error:
+	if (unlink(mtabtmpfile))
+		fprintf(stderr, "del_mtab: failed to delete tmp file - %s\n",
+				strerror(errno));
+	goto del_mtab_exit;
+}
+
 /* have the child drop root privileges */
 static int
 drop_child_privs(void)
@@ -2021,8 +2111,15 @@ mount_retry:
 	}
 
 do_mtab:
-	if (!parsed_info->nomtab && !mtab_unusable())
+	if (!parsed_info->nomtab && !mtab_unusable()) {
+		if (parsed_info->flags & MS_REMOUNT) {
+			rc = del_mtab(mountpoint);
+			if (rc)
+				goto mount_exit;
+		}
+
 		rc = add_mtab(orig_dev, mountpoint, parsed_info->flags, fstype);
+	}
 
 mount_exit:
 	if (parsed_info) {