autofs-5.0.3 - check for mtab pointing to /proc/mounts

From: Ian Kent <raven@themaw.net>

autofs has problems if /etc/mtab points to /proc/mounts.
This patchs adds a check to see if this is the case. If it is then
autofs uses the mount(8) "-n" option which disables the normal mtab
update error checking.
---

 daemon/spawn.c |   65 ++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 60 insertions(+), 5 deletions(-)


--- autofs-5.0.1.orig/daemon/spawn.c
+++ autofs-5.0.1/daemon/spawn.c
@@ -305,11 +305,13 @@ int spawn_mount(unsigned logopt, ...)
 	char **argv, **p;
 	char prog[] = PATH_MOUNT;
 	char arg0[] = PATH_MOUNT;
+	char argn[] = "-n";
 	/* In case we need to use the fake option to mount */
 	char arg_fake[] = "-f";
 	unsigned int options;
 	unsigned int retries = MTAB_LOCK_RETRIES;
-	int ret, printed = 0;
+	int update_mtab = 1, ret, printed = 0;
+	char buf[PATH_MAX];
 
 	/* If we use mount locking we can't validate the location */
 #ifdef ENABLE_MOUNT_LOCKING
@@ -322,6 +324,17 @@ int spawn_mount(unsigned logopt, ...)
 	for (argc = 1; va_arg(arg, char *); argc++);
 	va_end(arg);
 
+	ret = readlink(_PATH_MOUNTED, buf, PATH_MAX);
+	if (ret != -1) {
+		buf[ret] = '\0';
+		if (!strcmp(buf, _PROC_MOUNTS)) {
+			debug(logopt,
+			      "mtab link detected, passing -n to mount");
+			argc++;
+			update_mtab = 0;
+		}
+	}
+
 	/* Alloc 1 extra slot in case we need to use the "-f" option */
 	if (!(argv = alloca(sizeof(char *) * argc + 2)))
 		return -1;
@@ -329,7 +342,12 @@ int spawn_mount(unsigned logopt, ...)
 	argv[0] = arg0;
 
 	va_start(arg, logopt);
-	p = argv + 1;
+	if (update_mtab)
+		p = argv + 1;
+	else {
+		argv[1] = argn;
+		p = argv + 2;
+	}
 	while ((*p++ = va_arg(arg, char *)));
 	va_end(arg);
 
@@ -400,11 +418,13 @@ int spawn_bind_mount(unsigned logopt, ..
 	char prog[] = PATH_MOUNT;
 	char arg0[] = PATH_MOUNT;
 	char bind[] = "--bind";
+	char argn[] = "-n";
 	/* In case we need to use the fake option to mount */
 	char arg_fake[] = "-f";
 	unsigned int options;
 	unsigned int retries = MTAB_LOCK_RETRIES;
-	int ret, printed = 0;
+	int update_mtab = 1, ret, printed = 0;
+	char buf[PATH_MAX];
 
 	/* If we use mount locking we can't validate the location */
 #ifdef ENABLE_MOUNT_LOCKING
@@ -421,6 +441,17 @@ int spawn_bind_mount(unsigned logopt, ..
 	for (argc = 2; va_arg(arg, char *); argc++);
 	va_end(arg);
 
+	ret = readlink(_PATH_MOUNTED, buf, PATH_MAX);
+	if (ret != -1) {
+		buf[ret] = '\0';
+		if (!strcmp(buf, _PROC_MOUNTS)) {
+			debug(logopt,
+			      "mtab link detected, passing -n to mount");
+			argc++;
+			update_mtab = 0;
+		}
+	}
+
 	if (!(argv = alloca(sizeof(char *) * argc + 2)))
 		return -1;
 
@@ -428,7 +459,12 @@ int spawn_bind_mount(unsigned logopt, ..
 	argv[1] = bind;
 
 	va_start(arg, logopt);
-	p = argv + 2;
+	if (update_mtab)
+		p = argv + 2;
+	else {
+		argv[2] = argn;
+		p = argv + 3;
+	}
 	while ((*p++ = va_arg(arg, char *)));
 	va_end(arg);
 
@@ -490,10 +526,12 @@ int spawn_umount(unsigned logopt, ...)
 	char **argv, **p;
 	char prog[] = PATH_UMOUNT;
 	char arg0[] = PATH_UMOUNT;
+	char argn[] = "-n";
 	unsigned int options;
 	unsigned int retries = MTAB_LOCK_RETRIES;
-	int ret, printed = 0;
+	int update_mtab = 1, ret, printed = 0;
 	unsigned int wait = defaults_get_umount_wait();
+	char buf[PATH_MAX];
 
 #ifdef ENABLE_MOUNT_LOCKING
 	options = SPAWN_OPT_LOCK;
@@ -505,13 +543,29 @@ int spawn_umount(unsigned logopt, ...)
 	for (argc = 1; va_arg(arg, char *); argc++);
 	va_end(arg);
 
+	ret = readlink(_PATH_MOUNTED, buf, PATH_MAX);
+	if (ret != -1) {
+		buf[ret] = '\0';
+		if (!strcmp(buf, _PROC_MOUNTS)) {
+			debug(logopt,
+			      "mtab link detected, passing -n to mount");
+			argc++;
+			update_mtab = 0;
+		}
+	}
+
 	if (!(argv = alloca(sizeof(char *) * argc + 1)))
 		return -1;
 
 	argv[0] = arg0;
 
 	va_start(arg, logopt);
-	p = argv + 1;
+	if (update_mtab)
+		p = argv + 1;
+	else {
+		argv[1] = argn;
+		p = argv + 2;
+	}
 	while ((*p++ = va_arg(arg, char *)));
 	va_end(arg);