2024-02-04 02:18:01

by Al Viro

Subject: [PATCH 08/13] nfs: fix UAF on pathwalk running into umount

NFS ->d_revalidate(), ->permission() and ->get_link() need to access
some parts of nfs_server when called in RCU mode:
server->flags
server->caps
*(server->io_stats)
and, worst of all, call
server->nfs_client->rpc_ops->have_delegation
(the last one - as NFS_PROTO(inode)->have_delegation()). We really
don't want to RCU-delay the entire nfs_free_server() (it would have
to be done with schedule_work() from RCU callback, since it can't
be made to run from interrupt context), but actual freeing of
nfs_server and ->io_stats can be done via call_rcu() just fine.
nfs_client part is handled simply by making nfs_free_client() use
kfree_rcu().

Signed-off-by: Al Viro <[email protected]>
---
fs/nfs/client.c | 13 ++++++++++---
include/linux/nfs_fs_sb.h | 2 ++
2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 44eca51b2808..fbdc9ca80f71 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -246,7 +246,7 @@ void nfs_free_client(struct nfs_client *clp)
put_nfs_version(clp->cl_nfs_mod);
kfree(clp->cl_hostname);
kfree(clp->cl_acceptor);
- kfree(clp);
+ kfree_rcu(clp, rcu);
}
EXPORT_SYMBOL_GPL(nfs_free_client);

@@ -1006,6 +1006,14 @@ struct nfs_server *nfs_alloc_server(void)
}
EXPORT_SYMBOL_GPL(nfs_alloc_server);

+static void delayed_free(struct rcu_head *p)
+{
+ struct nfs_server *server = container_of(p, struct nfs_server, rcu);
+
+ nfs_free_iostats(server->io_stats);
+ kfree(server);
+}
+
/*
* Free up a server record
*/
@@ -1031,10 +1039,9 @@ void nfs_free_server(struct nfs_server *server)

ida_destroy(&server->lockowner_id);
ida_destroy(&server->openowner_id);
- nfs_free_iostats(server->io_stats);
put_cred(server->cred);
- kfree(server);
nfs_release_automount_timer();
+ call_rcu(&server->rcu, delayed_free);
}
EXPORT_SYMBOL_GPL(nfs_free_server);

diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index cd797e00fe35..92de074e63b9 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -124,6 +124,7 @@ struct nfs_client {
char cl_ipaddr[48];
struct net *cl_net;
struct list_head pending_cb_stateids;
+ struct rcu_head rcu;
};

/*
@@ -265,6 +266,7 @@ struct nfs_server {
const struct cred *cred;
bool has_sec_mnt_opts;
struct kobject kobj;
+ struct rcu_head rcu;
};

/* Server capabilities */
--
2.39.2

2024-02-05 12:32:28

by Christian Brauner

Subject: Re: [PATCH 08/13] nfs: fix UAF on pathwalk running into umount

On Sun, Feb 04, 2024 at 02:17:34AM +0000, Al Viro wrote:
> NFS ->d_revalidate(), ->permission() and ->get_link() need to access
> some parts of nfs_server when called in RCU mode:
> server->flags
> server->caps
> *(server->io_stats)
> and, worst of all, call
> server->nfs_client->rpc_ops->have_delegation
> (the last one - as NFS_PROTO(inode)->have_delegation()). We really
> don't want to RCU-delay the entire nfs_free_server() (it would have
> to be done with schedule_work() from RCU callback, since it can't
> be made to run from interrupt context), but actual freeing of
> nfs_server and ->io_stats can be done via call_rcu() just fine.
> nfs_client part is handled simply by making nfs_free_client() use
> kfree_rcu().
>
> Signed-off-by: Al Viro <[email protected]>
> ---

Acked-by: Christian Brauner <[email protected]>