[PATCH 6/6] Add an AT_NO_AUTOMOUNT flag to suppress terminal automount [ver #2]

David Howells
2010-07-23T15:11:22Z

This is an update required because the first patch in the series was also
altered in the same area.

David
---
From: David Howells <dhowells@redhat.com>
Subject: [PATCH] Add an AT_NO_AUTOMOUNT flag to suppress terminal automount

Add an AT_NO_AUTOMOUNT flag to suppress terminal automounting of directories
with follow_link semantics. This can be used by fstatat() users to permit the
gathering of attributes on an automount point and also prevent
mass-automounting of a directory of automount points by ls.

Signed-off-by: David Howells <dhowells@redhat.com>
---

fs/namei.c | 6 ++++++
fs/stat.c | 4 +++-
include/linux/fcntl.h | 1 +
include/linux/namei.h | 2 ++
4 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index f2910b7..c154112 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -629,6 +629,12 @@ static int follow_automount(struct path *path, unsigned flags, int res)
if (!path->dentry->d_op || !path->dentry->d_op->d_automount)
return -EREMOTE;

+ /* We don't want to mount if someone supplied AT_NO_AUTOMOUNT
+ * and this is the terminal part of the path.
+ */
+ if ((flags & LOOKUP_NO_AUTOMOUNT) && !(flags & LOOKUP_CONTINUE))
+ return -EXDEV; /* we actually want to stop here */
+
/* We want to mount if someone is trying to open/create a file of any
* type under the mountpoint, wants to traverse through the mountpoint
* or wants to open the mounted directory.
diff --git a/fs/stat.c b/fs/stat.c
index c4ecd52..bae6fa2 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -74,11 +74,13 @@ int vfs_fstatat(int dfd, char __user *filename, struct kstat *stat, int flag)
int error = -EINVAL;
int lookup_flags = 0;

- if ((flag & ~AT_SYMLINK_NOFOLLOW) != 0)
+ if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT)) != 0)
goto out;

if (!(flag & AT_SYMLINK_NOFOLLOW))
lookup_flags |= LOOKUP_FOLLOW;
+ if (flag & AT_NO_AUTOMOUNT)
+ lookup_flags |= LOOKUP_NO_AUTOMOUNT;

error = user_path_at(dfd, filename, lookup_flags, &path);
if (error)
diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h
index afc00af..a562fa5 100644
--- a/include/linux/fcntl.h
+++ b/include/linux/fcntl.h
@@ -45,6 +45,7 @@
#define AT_REMOVEDIR 0x200 /* Remove directory instead of
unlinking file. */
#define AT_SYMLINK_FOLLOW 0x400 /* Follow symbolic links. */
+#define AT_NO_AUTOMOUNT 0x800 /* Suppress terminal automount traversal */

#ifdef __KERNEL__

diff --git a/include/linux/namei.h b/include/linux/namei.h
index 05b441d..1e1febf 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -43,12 +43,14 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND};
* - internal "there are more path components" flag
* - locked when lookup done with dcache_lock held
* - dentry cache is untrusted; force a real lookup
+ * - suppress terminal automount
*/
#define LOOKUP_FOLLOW 1
#define LOOKUP_DIRECTORY 2
#define LOOKUP_CONTINUE 4
#define LOOKUP_PARENT 16
#define LOOKUP_REVAL 64
+#define LOOKUP_NO_AUTOMOUNT 128
/*
* Intent data
*/