When using a multi-mount with mount targets that are on the
local machine and resulting bind mounts are made to a file
system that is mount propagation shared (such as the root
file system on systemd managed systems) the autofs offset
mount triggers made within the bind mount will be propagated
back to the target file system.
When this happens the target of the offset (the unwanted
propagated mount) is itself an autofs trigger mount and
accessing the path results in a deadlock.
In order for these multi-mounts to function properly in this
case bind mounts that contain mount triggers must be set to
propagation slave or private so the backward propagation
doesn't occur.
Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
---
CHANGELOG | 1 +
modules/mount_bind.c | 16 +++++++++++++++-
2 files changed, 16 insertions(+), 1 deletion(-)
diff --git a/CHANGELOG b/CHANGELOG
index 42950d51..88829564 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -34,6 +34,7 @@ xx/xx/2018 autofs-5.1.5
- fix update_negative_cache() map source usage.
- fix program usage message.
- mark removed cache entry negative.
+- set bind mount as propagation slave.
19/12/2017 autofs-5.1.4
- fix spec file url.
diff --git a/modules/mount_bind.c b/modules/mount_bind.c
index 5effa880..fe1ad9b6 100644
--- a/modules/mount_bind.c
+++ b/modules/mount_bind.c
@@ -20,6 +20,7 @@
#include <sys/param.h>
#include <sys/types.h>
#include <sys/stat.h>
+#include <sys/mount.h>
#define MODULE_MOUNT
#include "automount.h"
@@ -183,8 +184,21 @@ int mount_mount(struct autofs_point *ap, const char *root, const char *name, int
debug(ap->logopt,
MODPREFIX "mounted %s type %s on %s",
what, fstype, fullpath);
- return 0;
}
+
+ /* The bind mount has succeeded but if the target
+ * mount is propagation shared propagation of child
+ * mounts (autofs offset mounts for example) back to
+ * the target of the bind mount must be avoided or
+ * autofs trigger mounts will deadlock.
+ */
+ err = mount(NULL, fullpath, NULL, MS_SLAVE, NULL);
+ if (err)
+ warn(ap->logopt,
+ "failed to set propagation type for %s",
+ fullpath);
+
+ return 0;
} else {
char *cp;
char basepath[PATH_MAX];
