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

David Howells
2010-07-22T17:59:36Z

Add an AT_NO_AUTOMOUNT flag to suppress terminal automounting of directories
with follow_link semantics. This can be used by fstatat()/xstat() 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 | 15 ++++++++++-----
fs/stat.c | 4 +++-
include/linux/fcntl.h | 1 +
include/linux/namei.h | 2 ++
4 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 86068a2..056427e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -654,7 +654,8 @@ static int follow_automount(struct path *path, int res)
/* no need for dcache_lock, as serialization is taken care in
* namespace.c
*/
-static int __follow_mount(struct path *path, unsigned nofollow)
+static int __follow_mount(struct path *path, unsigned nofollow,
+ struct nameidata *nd)
{
struct vfsmount *mounted;
int ret, res = 0;
@@ -674,8 +675,12 @@ static int __follow_mount(struct path *path, unsigned nofollow)
}
if (!d_automount_point(path->dentry))
break;
- if (nofollow)
- return -ELOOP;
+ if (!(nd->flags & LOOKUP_CONTINUE)) {
+ if (nofollow)
+ return -ELOOP;
+ if (nd->flags & LOOKUP_NO_AUTOMOUNT)
+ break;
+ }
ret = follow_automount(path, res);
if (ret < 0)
return ret;
@@ -769,7 +774,7 @@ static int do_lookup(struct nameidata *nd, struct qstr *name,
done:
path->mnt = mnt;
path->dentry = dentry;
- ret = __follow_mount(path, 0);
+ ret = __follow_mount(path, 0, nd);
if (unlikely(ret < 0))
path_put(path);
return ret;
@@ -1762,7 +1767,7 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
if (open_flag & O_EXCL)
goto exit_dput;

- error = __follow_mount(path, open_flag & O_NOFOLLOW);
+ error = __follow_mount(path, open_flag & O_NOFOLLOW, nd);
if (error < 0)
goto exit_dput;

diff --git a/fs/stat.c b/fs/stat.c
index c4ecd52..e4662de 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
*/