Re: [PATCH v5 2/4] fuse: Support fuse filesystems outside of init_user_ns
From: Andy Lutomirski
Date: Wed Oct 22 2014 - 17:47:57 EST
On Wed, Oct 22, 2014 at 2:24 PM, Seth Forshee
<seth.forshee@xxxxxxxxxxxxx> wrote:
> Update fuse to translate uids and gids to/from the user namspace
> of the process servicing requests on /dev/fuse. Any ids which do
> not map into the namespace will result in errors. inodes will
> also be marked bad when unmappable ids are received from
> userspace.
>
> Due to security concerns the namespace used should be fixed,
> otherwise a user might be able to gain elevated privileges or
> influence processes that the user would otherwise be unable to
> manipulate. Thus the namespace of the mounting process is used
> for all translations, and this namespace is required to be the
> same as the one in use when /dev/fuse was opened.
Looks generally sensible to me. I'm not familiar enough with this
code to really review it, though.
>
> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: Serge H. Hallyn <serge.hallyn@xxxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> Signed-off-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
> ---
> fs/fuse/dev.c | 4 +--
> fs/fuse/dir.c | 81 ++++++++++++++++++++++++++++++++++++--------------------
> fs/fuse/fuse_i.h | 12 ++++++---
> fs/fuse/inode.c | 73 +++++++++++++++++++++++++++++++++++++++-----------
> 4 files changed, 121 insertions(+), 49 deletions(-)
>
> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> index 839caebd34f1..03c8785ed731 100644
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -127,8 +127,8 @@ static void __fuse_put_request(struct fuse_req *req)
>
> static void fuse_req_init_context(struct fuse_conn *fc, struct fuse_req *req)
> {
> - req->in.h.uid = from_kuid_munged(&init_user_ns, current_fsuid());
> - req->in.h.gid = from_kgid_munged(&init_user_ns, current_fsgid());
> + req->in.h.uid = from_kuid_munged(fc->user_ns, current_fsuid());
> + req->in.h.gid = from_kgid_munged(fc->user_ns, current_fsgid());
> req->in.h.pid = pid_nr_ns(task_pid(current), fc->pid_ns);
> }
>
> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index de1d84af9f7c..123db1e06c78 100644
> --- a/fs/fuse/dir.c
> +++ b/fs/fuse/dir.c
> @@ -253,9 +253,12 @@ static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags)
> if (err || (outarg.attr.mode ^ inode->i_mode) & S_IFMT)
> goto invalid;
>
> - fuse_change_attributes(inode, &outarg.attr,
> - entry_attr_timeout(&outarg),
> - attr_version);
> + err = fuse_change_attributes(inode, &outarg.attr,
> + entry_attr_timeout(&outarg),
> + attr_version);
> + if (err)
> + goto invalid;
> +
> fuse_change_entry_timeout(entry, &outarg);
> } else if (inode) {
> fi = get_fuse_inode(inode);
> @@ -340,8 +343,9 @@ int fuse_lookup_name(struct super_block *sb, u64 nodeid, struct qstr *name,
> *inode = fuse_iget(sb, outarg->nodeid, outarg->generation,
> &outarg->attr, entry_attr_timeout(outarg),
> attr_version);
> - err = -ENOMEM;
> - if (!*inode) {
> + if (IS_ERR(*inode)) {
> + err = PTR_ERR(*inode);
> + *inode = NULL;
> fuse_queue_forget(fc, forget, outarg->nodeid, 1);
> goto out;
> }
> @@ -473,11 +477,11 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
> ff->open_flags = outopen.open_flags;
> inode = fuse_iget(dir->i_sb, outentry.nodeid, outentry.generation,
> &outentry.attr, entry_attr_timeout(&outentry), 0);
> - if (!inode) {
> + if (IS_ERR(inode)) {
> flags &= ~(O_CREAT | O_EXCL | O_TRUNC);
> fuse_sync_release(ff, flags);
> fuse_queue_forget(fc, forget, outentry.nodeid, 1);
> - err = -ENOMEM;
> + err = PTR_ERR(inode);
> goto out_err;
> }
> kfree(forget);
> @@ -588,9 +592,9 @@ static int create_new_entry(struct fuse_conn *fc, struct fuse_req *req,
>
> inode = fuse_iget(dir->i_sb, outarg.nodeid, outarg.generation,
> &outarg.attr, entry_attr_timeout(&outarg), 0);
> - if (!inode) {
> + if (IS_ERR(inode)) {
> fuse_queue_forget(fc, forget, outarg.nodeid, 1);
> - return -ENOMEM;
> + return PTR_ERR(inode);
> }
> kfree(forget);
>
> @@ -905,8 +909,8 @@ static void fuse_fillattr(struct inode *inode, struct fuse_attr *attr,
> stat->ino = attr->ino;
> stat->mode = (inode->i_mode & S_IFMT) | (attr->mode & 07777);
> stat->nlink = attr->nlink;
> - stat->uid = make_kuid(&init_user_ns, attr->uid);
> - stat->gid = make_kgid(&init_user_ns, attr->gid);
> + stat->uid = inode->i_uid;
> + stat->gid = inode->i_gid;
> stat->rdev = inode->i_rdev;
> stat->atime.tv_sec = attr->atime;
> stat->atime.tv_nsec = attr->atimensec;
> @@ -969,10 +973,10 @@ static int fuse_do_getattr(struct inode *inode, struct kstat *stat,
> make_bad_inode(inode);
> err = -EIO;
> } else {
> - fuse_change_attributes(inode, &outarg.attr,
> - attr_timeout(&outarg),
> - attr_version);
> - if (stat)
> + err = fuse_change_attributes(inode, &outarg.attr,
> + attr_timeout(&outarg),
> + attr_version);
> + if (!err && stat)
> fuse_fillattr(inode, &outarg.attr, stat);
> }
> }
> @@ -1302,9 +1306,11 @@ static int fuse_direntplus_link(struct file *file,
> fi->nlookup++;
> spin_unlock(&fc->lock);
>
> - fuse_change_attributes(inode, &o->attr,
> - entry_attr_timeout(o),
> - attr_version);
> + err = fuse_change_attributes(inode, &o->attr,
> + entry_attr_timeout(o),
> + attr_version);
> + if (err)
> + goto out;
>
> /*
> * The other branch to 'found' comes via fuse_iget()
> @@ -1322,8 +1328,10 @@ static int fuse_direntplus_link(struct file *file,
>
> inode = fuse_iget(dir->i_sb, o->nodeid, o->generation,
> &o->attr, entry_attr_timeout(o), attr_version);
> - if (!inode)
> + if (IS_ERR(inode)) {
> + err = PTR_ERR(inode);
> goto out;
> + }
>
> alias = d_materialise_unique(dentry, inode);
> err = PTR_ERR(alias);
> @@ -1556,17 +1564,25 @@ static bool update_mtime(unsigned ivalid, bool trust_local_mtime)
> return true;
> }
>
> -static void iattr_to_fattr(struct iattr *iattr, struct fuse_setattr_in *arg,
> - bool trust_local_cmtime)
> +static int iattr_to_fattr(struct fuse_conn *fc, struct iattr *iattr,
> + struct fuse_setattr_in *arg, bool trust_local_cmtime)
> {
> unsigned ivalid = iattr->ia_valid;
>
> if (ivalid & ATTR_MODE)
> arg->valid |= FATTR_MODE, arg->mode = iattr->ia_mode;
> - if (ivalid & ATTR_UID)
> - arg->valid |= FATTR_UID, arg->uid = from_kuid(&init_user_ns, iattr->ia_uid);
> - if (ivalid & ATTR_GID)
> - arg->valid |= FATTR_GID, arg->gid = from_kgid(&init_user_ns, iattr->ia_gid);
> + if (ivalid & ATTR_UID) {
> + arg->uid = from_kuid(fc->user_ns, iattr->ia_uid);
> + if (arg->uid == (uid_t)-1)
> + return -EINVAL;
> + arg->valid |= FATTR_UID;
> + }
> + if (ivalid & ATTR_GID) {
> + arg->gid = from_kgid(fc->user_ns, iattr->ia_gid);
> + if (arg->gid == (gid_t)-1)
> + return -EINVAL;
> + arg->valid |= FATTR_GID;
> + }
> if (ivalid & ATTR_SIZE)
> arg->valid |= FATTR_SIZE, arg->size = iattr->ia_size;
> if (ivalid & ATTR_ATIME) {
> @@ -1588,6 +1604,8 @@ static void iattr_to_fattr(struct iattr *iattr, struct fuse_setattr_in *arg,
> arg->ctime = iattr->ia_ctime.tv_sec;
> arg->ctimensec = iattr->ia_ctime.tv_nsec;
> }
> +
> + return 0;
> }
>
> /*
> @@ -1741,7 +1759,9 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,
>
> memset(&inarg, 0, sizeof(inarg));
> memset(&outarg, 0, sizeof(outarg));
> - iattr_to_fattr(attr, &inarg, trust_local_cmtime);
> + err = iattr_to_fattr(fc, attr, &inarg, trust_local_cmtime);
> + if (err)
> + goto error;
> if (file) {
> struct fuse_file *ff = file->private_data;
> inarg.valid |= FATTR_FH;
> @@ -1778,8 +1798,13 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,
> /* FIXME: clear I_DIRTY_SYNC? */
> }
>
> - fuse_change_attributes_common(inode, &outarg.attr,
> - attr_timeout(&outarg));
> + err = fuse_change_attributes_common(inode, &outarg.attr,
> + attr_timeout(&outarg));
> + if (err) {
> + spin_unlock(&fc->lock);
> + goto error;
> + }
> +
> oldsize = inode->i_size;
> /* see the comment in fuse_change_attributes() */
> if (!is_wb || is_truncate || !S_ISREG(inode->i_mode))
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index a3ded071e2c6..81187ba04e4a 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -22,6 +22,7 @@
> #include <linux/rbtree.h>
> #include <linux/poll.h>
> #include <linux/workqueue.h>
> +#include <linux/user_namespace.h>
> #include <linux/pid_namespace.h>
>
> /** Max number of pages that can be used in a single read request */
> @@ -387,6 +388,9 @@ struct fuse_conn {
> /** The group id for this mount */
> kgid_t group_id;
>
> + /** The user namespace for this mount */
> + struct user_namespace *user_ns;
> +
> /** The pid namespace for this mount */
> struct pid_namespace *pid_ns;
>
> @@ -713,11 +717,11 @@ void fuse_init_symlink(struct inode *inode);
> /**
> * Change attributes of an inode
> */
> -void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
> - u64 attr_valid, u64 attr_version);
> +int fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
> + u64 attr_valid, u64 attr_version);
>
> -void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
> - u64 attr_valid);
> +int fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
> + u64 attr_valid);
>
> /**
> * Initialize the client device
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index e137969815a3..b88b5a780228 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -155,11 +155,22 @@ static ino_t fuse_squash_ino(u64 ino64)
> return ino;
> }
>
> -void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
> - u64 attr_valid)
> +int fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
> + u64 attr_valid)
> {
> struct fuse_conn *fc = get_fuse_conn(inode);
> struct fuse_inode *fi = get_fuse_inode(inode);
> + kuid_t uid;
> + kgid_t gid;
> +
> + uid = make_kuid(fc->user_ns, attr->uid);
> + gid = make_kgid(fc->user_ns, attr->gid);
> + if (!uid_valid(uid) || !gid_valid(gid)) {
> + make_bad_inode(inode);
> + return -EIO;
> + }
> + inode->i_uid = uid;
> + inode->i_gid = gid;
>
> fi->attr_version = ++fc->attr_version;
> fi->i_time = attr_valid;
> @@ -167,8 +178,6 @@ void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
> inode->i_ino = fuse_squash_ino(attr->ino);
> inode->i_mode = (inode->i_mode & S_IFMT) | (attr->mode & 07777);
> set_nlink(inode, attr->nlink);
> - inode->i_uid = make_kuid(&init_user_ns, attr->uid);
> - inode->i_gid = make_kgid(&init_user_ns, attr->gid);
> inode->i_blocks = attr->blocks;
> inode->i_atime.tv_sec = attr->atime;
> inode->i_atime.tv_nsec = attr->atimensec;
> @@ -195,26 +204,32 @@ void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
> inode->i_mode &= ~S_ISVTX;
>
> fi->orig_ino = attr->ino;
> + return 0;
> }
>
> -void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
> - u64 attr_valid, u64 attr_version)
> +int fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
> + u64 attr_valid, u64 attr_version)
> {
> struct fuse_conn *fc = get_fuse_conn(inode);
> struct fuse_inode *fi = get_fuse_inode(inode);
> bool is_wb = fc->writeback_cache;
> loff_t oldsize;
> struct timespec old_mtime;
> + int err;
>
> spin_lock(&fc->lock);
> if ((attr_version != 0 && fi->attr_version > attr_version) ||
> test_bit(FUSE_I_SIZE_UNSTABLE, &fi->state)) {
> spin_unlock(&fc->lock);
> - return;
> + return 0;
> }
>
> old_mtime = inode->i_mtime;
> - fuse_change_attributes_common(inode, attr, attr_valid);
> + err = fuse_change_attributes_common(inode, attr, attr_valid);
> + if (err) {
> + spin_unlock(&fc->lock);
> + return err;
> + }
>
> oldsize = inode->i_size;
> /*
> @@ -249,6 +264,8 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
> if (inval)
> invalidate_inode_pages2(inode->i_mapping);
> }
> +
> + return 0;
> }
>
> static void fuse_init_inode(struct inode *inode, struct fuse_attr *attr)
> @@ -302,7 +319,7 @@ struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
> retry:
> inode = iget5_locked(sb, nodeid, fuse_inode_eq, fuse_inode_set, &nodeid);
> if (!inode)
> - return NULL;
> + return ERR_PTR(-ENOMEM);
>
> if ((inode->i_state & I_NEW)) {
> inode->i_flags |= S_NOATIME;
> @@ -319,11 +336,23 @@ struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
> goto retry;
> }
>
> + /*
> + * Must do this before incrementing nlookup, as the caller will
> + * send a forget for the node if this function fails.
> + */
> + if (fuse_change_attributes(inode, attr, attr_valid, attr_version)) {
> + /*
> + * inode_make_bad() already called by
> + * fuse_change_attributes()
> + */
> + iput(inode);
> + return ERR_PTR(-EIO);
> + }
> +
> fi = get_fuse_inode(inode);
> spin_lock(&fc->lock);
> fi->nlookup++;
> spin_unlock(&fc->lock);
> - fuse_change_attributes(inode, attr, attr_valid, attr_version);
>
> return inode;
> }
> @@ -496,6 +525,8 @@ static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev)
> memset(d, 0, sizeof(struct fuse_mount_data));
> d->max_read = ~0;
> d->blksize = FUSE_DEFAULT_BLKSIZE;
> + d->user_id = make_kuid(current_user_ns(), 0);
> + d->group_id = make_kgid(current_user_ns(), 0);
>
> while ((p = strsep(&opt, ",")) != NULL) {
> int token;
> @@ -578,8 +609,10 @@ static int fuse_show_options(struct seq_file *m, struct dentry *root)
> struct super_block *sb = root->d_sb;
> struct fuse_conn *fc = get_fuse_conn_super(sb);
>
> - seq_printf(m, ",user_id=%u", from_kuid_munged(&init_user_ns, fc->user_id));
> - seq_printf(m, ",group_id=%u", from_kgid_munged(&init_user_ns, fc->group_id));
> + seq_printf(m, ",user_id=%u",
> + from_kuid_munged(fc->user_ns, fc->user_id));
> + seq_printf(m, ",group_id=%u",
> + from_kgid_munged(fc->user_ns, fc->group_id));
> if (fc->flags & FUSE_DEFAULT_PERMISSIONS)
> seq_puts(m, ",default_permissions");
> if (fc->flags & FUSE_ALLOW_OTHER)
> @@ -618,6 +651,7 @@ void fuse_conn_init(struct fuse_conn *fc)
> fc->attr_version = 1;
> get_random_bytes(&fc->scramble_key, sizeof(fc->scramble_key));
> fc->pid_ns = get_pid_ns(task_active_pid_ns(current));
> + fc->user_ns = get_user_ns(current_user_ns());
> }
> EXPORT_SYMBOL_GPL(fuse_conn_init);
>
> @@ -626,6 +660,8 @@ void fuse_conn_put(struct fuse_conn *fc)
> if (atomic_dec_and_test(&fc->count)) {
> if (fc->destroy_req)
> fuse_request_free(fc->destroy_req);
> + put_user_ns(fc->user_ns);
> + fc->user_ns = NULL;
> put_pid_ns(fc->pid_ns);
> fc->pid_ns = NULL;
> fc->release(fc);
> @@ -643,12 +679,15 @@ EXPORT_SYMBOL_GPL(fuse_conn_get);
> static struct inode *fuse_get_root_inode(struct super_block *sb, unsigned mode)
> {
> struct fuse_attr attr;
> + struct inode *inode;
> +
> memset(&attr, 0, sizeof(attr));
>
> attr.mode = mode;
> attr.ino = FUSE_ROOT_ID;
> attr.nlink = 1;
> - return fuse_iget(sb, 1, 0, &attr, 0, 0);
> + inode = fuse_iget(sb, 1, 0, &attr, 0, 0);
> + return IS_ERR(inode) ? NULL : inode;
> }
>
> struct fuse_inode_handle {
> @@ -1043,8 +1082,12 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
> if (!file)
> goto err;
>
> - if ((file->f_op != &fuse_dev_operations) ||
> - (file->f_cred->user_ns != &init_user_ns))
> + /*
> + * Require mount to happen from the same user namespace which
> + * opened /dev/fuse to prevent potential attacks.
> + */
> + if (file->f_op != &fuse_dev_operations ||
> + file->f_cred->user_ns != current_user_ns())
> goto err_fput;
>
> fc = kmalloc(sizeof(*fc), GFP_KERNEL);
> --
> 1.9.1
>
--
Andy Lutomirski
AMA Capital Management, LLC
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