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author | Eric W. Biederman <ebiederm@xmission.com> | 2017-02-01 06:06:16 +1300 |
---|---|---|
committer | Eric W. Biederman <ebiederm@xmission.com> | 2017-02-02 04:36:12 +1300 |
commit | 93faccbbfa958a9668d3ab4e30f38dd205cee8d8 (patch) | |
tree | f4a102b92d86d19a52a88a57bdde19ad25250ca1 /fs | |
parent | c6c70f4455d1eda91065e93cc4f7eddf4499b105 (diff) | |
download | linux-stable-93faccbbfa958a9668d3ab4e30f38dd205cee8d8.tar.gz linux-stable-93faccbbfa958a9668d3ab4e30f38dd205cee8d8.tar.bz2 linux-stable-93faccbbfa958a9668d3ab4e30f38dd205cee8d8.zip |
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')
-rw-r--r-- | fs/afs/mntpt.c | 2 | ||||
-rw-r--r-- | fs/autofs4/waitq.c | 4 | ||||
-rw-r--r-- | fs/cifs/cifs_dfs_ref.c | 7 | ||||
-rw-r--r-- | fs/debugfs/inode.c | 8 | ||||
-rw-r--r-- | fs/namei.c | 3 | ||||
-rw-r--r-- | fs/namespace.c | 17 | ||||
-rw-r--r-- | fs/nfs/namespace.c | 2 | ||||
-rw-r--r-- | fs/nfs/nfs4namespace.c | 2 | ||||
-rw-r--r-- | fs/super.c | 13 |
9 files changed, 39 insertions, 19 deletions
diff --git a/fs/afs/mntpt.c b/fs/afs/mntpt.c index 81dd075356b9..d4fb0afc0097 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); diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c index 1278335ce366..79fbd85db4ba 100644 --- a/fs/autofs4/waitq.c +++ b/fs/autofs4/waitq.c @@ -436,8 +436,8 @@ int autofs4_wait(struct autofs_sb_info *sbi, memcpy(&wq->name, &qstr, sizeof(struct qstr)); wq->dev = autofs4_get_dev(sbi); wq->ino = autofs4_get_ino(sbi); - wq->uid = current_real_cred()->uid; - wq->gid = current_real_cred()->gid; + wq->uid = current_cred()->uid; + wq->gid = current_cred()->gid; wq->pid = pid; wq->tgid = tgid; wq->status = -EINTR; /* Status return if interrupted */ diff --git a/fs/cifs/cifs_dfs_ref.c b/fs/cifs/cifs_dfs_ref.c index ec9dbbcca3b9..9156be545b0f 100644 --- a/fs/cifs/cifs_dfs_ref.c +++ b/fs/cifs/cifs_dfs_ref.c @@ -245,7 +245,8 @@ compose_mount_options_err: * @fullpath: full path in UNC format * @ref: server's referral */ -static struct vfsmount *cifs_dfs_do_refmount(struct cifs_sb_info *cifs_sb, +static struct vfsmount *cifs_dfs_do_refmount(struct dentry *mntpt, + struct cifs_sb_info *cifs_sb, const char *fullpath, const struct dfs_info3_param *ref) { struct vfsmount *mnt; @@ -259,7 +260,7 @@ static struct vfsmount *cifs_dfs_do_refmount(struct cifs_sb_info *cifs_sb, if (IS_ERR(mountdata)) return (struct vfsmount *)mountdata; - mnt = vfs_kern_mount(&cifs_fs_type, 0, devname, mountdata); + mnt = vfs_submount(mntpt, &cifs_fs_type, devname, mountdata); kfree(mountdata); kfree(devname); return mnt; @@ -334,7 +335,7 @@ static struct vfsmount *cifs_dfs_do_automount(struct dentry *mntpt) mnt = ERR_PTR(-EINVAL); break; } - mnt = cifs_dfs_do_refmount(cifs_sb, + mnt = cifs_dfs_do_refmount(mntpt, cifs_sb, full_path, referrals + i); cifs_dbg(FYI, "%s: cifs_dfs_do_refmount:%s , mnt:%p\n", __func__, referrals[i].node_name, mnt); diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c index f17fcf89e18e..1e30f74a9527 100644 --- a/fs/debugfs/inode.c +++ b/fs/debugfs/inode.c @@ -187,9 +187,9 @@ static const struct super_operations debugfs_super_operations = { static struct vfsmount *debugfs_automount(struct path *path) { - struct vfsmount *(*f)(void *); - f = (struct vfsmount *(*)(void *))path->dentry->d_fsdata; - return f(d_inode(path->dentry)->i_private); + debugfs_automount_t f; + f = (debugfs_automount_t)path->dentry->d_fsdata; + return f(path->dentry, d_inode(path->dentry)->i_private); } static const struct dentry_operations debugfs_dops = { @@ -504,7 +504,7 @@ EXPORT_SYMBOL_GPL(debugfs_create_dir); */ struct dentry *debugfs_create_automount(const char *name, struct dentry *parent, - struct vfsmount *(*f)(void *), + debugfs_automount_t f, void *data) { struct dentry *dentry = start_creating(name, parent); diff --git a/fs/namei.c b/fs/namei.c index 6fa3e9138fe4..da689c9c005e 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1100,7 +1100,6 @@ static int follow_automount(struct path *path, struct nameidata *nd, bool *need_mntput) { struct vfsmount *mnt; - const struct cred *old_cred; int err; if (!path->dentry->d_op || !path->dentry->d_op->d_automount) @@ -1129,9 +1128,7 @@ static int follow_automount(struct path *path, struct nameidata *nd, if (nd->total_link_count >= 40) return -ELOOP; - old_cred = override_creds(&init_cred); mnt = path->dentry->d_op->d_automount(path); - revert_creds(old_cred); if (IS_ERR(mnt)) { /* * The filesystem is allowed to return -EISDIR here to indicate diff --git a/fs/namespace.c b/fs/namespace.c index 487ba30bb5c6..089a6b23135a 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -989,6 +989,21 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void } EXPORT_SYMBOL_GPL(vfs_kern_mount); +struct vfsmount * +vfs_submount(const struct dentry *mountpoint, struct file_system_type *type, + const char *name, void *data) +{ + /* Until it is worked out how to pass the user namespace + * through from the parent mount to the submount don't support + * unprivileged mounts with submounts. + */ + if (mountpoint->d_sb->s_user_ns != &init_user_ns) + return ERR_PTR(-EPERM); + + return vfs_kern_mount(type, MS_SUBMOUNT, name, data); +} +EXPORT_SYMBOL_GPL(vfs_submount); + static struct mount *clone_mnt(struct mount *old, struct dentry *root, int flag) { @@ -2794,7 +2809,7 @@ long do_mount(const char *dev_name, const char __user *dir_name, flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN | MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT | - MS_STRICTATIME | MS_NOREMOTELOCK); + MS_STRICTATIME | MS_NOREMOTELOCK | MS_SUBMOUNT); if (flags & MS_REMOUNT) retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags, 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; } diff --git a/fs/super.c b/fs/super.c index 1709ed029a2c..4185844f7a12 100644 --- a/fs/super.c +++ b/fs/super.c @@ -469,7 +469,7 @@ struct super_block *sget_userns(struct file_system_type *type, struct super_block *old; int err; - if (!(flags & MS_KERNMOUNT) && + if (!(flags & (MS_KERNMOUNT|MS_SUBMOUNT)) && !(type->fs_flags & FS_USERNS_MOUNT) && !capable(CAP_SYS_ADMIN)) return ERR_PTR(-EPERM); @@ -499,7 +499,7 @@ retry: } if (!s) { spin_unlock(&sb_lock); - s = alloc_super(type, flags, user_ns); + s = alloc_super(type, (flags & ~MS_SUBMOUNT), user_ns); if (!s) return ERR_PTR(-ENOMEM); goto retry; @@ -540,8 +540,15 @@ struct super_block *sget(struct file_system_type *type, { struct user_namespace *user_ns = current_user_ns(); + /* We don't yet pass the user namespace of the parent + * mount through to here so always use &init_user_ns + * until that changes. + */ + if (flags & MS_SUBMOUNT) + user_ns = &init_user_ns; + /* Ensure the requestor has permissions over the target filesystem */ - if (!(flags & MS_KERNMOUNT) && !ns_capable(user_ns, CAP_SYS_ADMIN)) + if (!(flags & (MS_KERNMOUNT|MS_SUBMOUNT)) && !ns_capable(user_ns, CAP_SYS_ADMIN)) return ERR_PTR(-EPERM); return sget_userns(type, test, set, flags, user_ns, data); |