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authorEric W. Biederman <ebiederm@xmission.com>2017-02-01 06:06:16 +1300
committerEric W. Biederman <ebiederm@xmission.com>2017-02-02 04:36:12 +1300
commit93faccbbfa958a9668d3ab4e30f38dd205cee8d8 (patch)
treef4a102b92d86d19a52a88a57bdde19ad25250ca1 /fs/nfs
parentc6c70f4455d1eda91065e93cc4f7eddf4499b105 (diff)
fs: Better permission checking for submounts
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. Cc: stable@vger.kernel.org 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>
Diffstat (limited to 'fs/nfs')
-rw-r--r--fs/nfs/namespace.c2
-rw-r--r--fs/nfs/nfs4namespace.c2
2 files changed, 2 insertions, 2 deletions
diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c
index 5551e8ef67fd..e49d831c4e85 100644
--- a/fs/nfs/namespace.c
+++ b/fs/nfs/namespace.c
@@ -226,7 +226,7 @@ static struct vfsmount *nfs_do_clone_mount(struct nfs_server *server,
const char *devname,
struct nfs_clone_mount *mountdata)
{
- return vfs_kern_mount(&nfs_xdev_fs_type, 0, devname, mountdata);
+ return vfs_submount(mountdata->dentry, &nfs_xdev_fs_type, devname, mountdata);
}
/**
diff --git a/fs/nfs/nfs4namespace.c b/fs/nfs/nfs4namespace.c
index d21104912676..d8b040bd9814 100644
--- a/fs/nfs/nfs4namespace.c
+++ b/fs/nfs/nfs4namespace.c
@@ -279,7 +279,7 @@ static struct vfsmount *try_location(struct nfs_clone_mount *mountdata,
mountdata->hostname,
mountdata->mnt_path);
- mnt = vfs_kern_mount(&nfs4_referral_fs_type, 0, page, mountdata);
+ mnt = vfs_submount(mountdata->dentry, &nfs4_referral_fs_type, page, mountdata);
if (!IS_ERR(mnt))
break;
}