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authorEric W. Biederman <ebiederm@xmission.com>2017-01-31 17:06:16 (GMT)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-03-15 02:02:44 (GMT)
commitd3381fab77cbca6f9664cf49b3f5dd3171f1f6d3 (patch)
tree1b50cb1e44acabab069caf9c03b90dcf2b621877 /fs/afs
parent48e2181b0b8d1a1e226b2932a11d6f94aef28fb8 (diff)
downloadlinux-d3381fab77cbca6f9664cf49b3f5dd3171f1f6d3.tar.xz
fs: Better permission checking for submounts
commit 93faccbbfa958a9668d3ab4e30f38dd205cee8d8 upstream. To support unprivileged users mounting filesystems two permission checks have to be performed: a test to see if the user allowed to create a mount in the mount namespace, and a test to see if the user is allowed to access the specified filesystem. The automount case is special in that mounting the original filesystem grants permission to mount the sub-filesystems, to any user who happens to stumble across the their mountpoint and satisfies the ordinary filesystem permission checks. Attempting to handle the automount case by using override_creds almost works. It preserves the idea that permission to mount the original filesystem is permission to mount the sub-filesystem. Unfortunately using override_creds messes up the filesystems ordinary permission checks. Solve this by being explicit that a mount is a submount by introducing vfs_submount, and using it where appropriate. vfs_submount uses a new mount internal mount flags MS_SUBMOUNT, to let sget and friends know that a mount is a submount so they can take appropriate action. sget and sget_userns are modified to not perform any permission checks on submounts. follow_automount is modified to stop using override_creds as that has proven problemantic. do_mount is modified to always remove the new MS_SUBMOUNT flag so that we know userspace will never by able to specify it. autofs4 is modified to stop using current_real_cred that was put in there to handle the previous version of submount permission checking. cifs is modified to pass the mountpoint all of the way down to vfs_submount. debugfs is modified to pass the mountpoint all of the way down to trace_automount by adding a new parameter. To make this change easier a new typedef debugfs_automount_t is introduced to capture the type of the debugfs automount function. Fixes: 069d5ac9ae0d ("autofs: Fix automounts by using current_real_cred()->uid") Fixes: aeaa4a79ff6a ("fs: Call d_automount with the filesystems creds") Reviewed-by: Trond Myklebust <trond.myklebust@primarydata.com> Reviewed-by: Seth Forshee <seth.forshee@canonical.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs/afs')
-rw-r--r--fs/afs/mntpt.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/afs/mntpt.c b/fs/afs/mntpt.c
index 81dd075..d4fb0af 100644
--- a/fs/afs/mntpt.c
+++ b/fs/afs/mntpt.c
@@ -202,7 +202,7 @@ static struct vfsmount *afs_mntpt_do_automount(struct dentry *mntpt)
/* try and do the mount */
_debug("--- attempting mount %s -o %s ---", devname, options);
- mnt = vfs_kern_mount(&afs_fs_type, 0, devname, options);
+ mnt = vfs_submount(mntpt, &afs_fs_type, devname, options);
_debug("--- mount result %p ---", mnt);
free_page((unsigned long) devname);