nfs: fix ->d_revalidate() UAF on ->d_name accesses

Pass the stable name all the way down to ->rpc_ops->lookup() instances.

Note that passing &dentry->d_name is safe in e.g. nfs_lookup() - it *is*
stable there, as it is in ->create() et.al.

dget_parent() in nfs_instantiate() should be redundant - it'd better be
stable there; if it's not, we have more trouble, since ->d_name would
also be unsafe in such case.

nfs_submount() and nfs4_submount() may or may not require fixes - if
they ever get moved on server with fhandle preserved, we are in trouble
there...

UAF window is fairly narrow here and exfiltration requires the ability
to watch the traffic.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 10 insertions, 10 deletions

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 405f17e6e0b4..4d85068e820d 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -4536,15 +4536,15 @@ nfs4_proc_setattr(struct dentry *dentry, struct nfs_fattr *fattr,
 }
 
 static int _nfs4_proc_lookup(struct rpc_clnt *clnt, struct inode *dir,
-		struct dentry *dentry, struct nfs_fh *fhandle,
-		struct nfs_fattr *fattr)
+		struct dentry *dentry, const struct qstr *name,
+		struct nfs_fh *fhandle, struct nfs_fattr *fattr)
 {
 	struct nfs_server *server = NFS_SERVER(dir);
 	int		       status;
 	struct nfs4_lookup_arg args = {
 		.bitmask = server->attr_bitmask,
 		.dir_fh = NFS_FH(dir),
-		.name = &dentry->d_name,
+		.name = name,
 	};
 	struct nfs4_lookup_res res = {
 		.server = server,
@@ -4586,17 +4586,16 @@ static void nfs_fixup_secinfo_attributes(struct nfs_fattr *fattr)
 }
 
 static int nfs4_proc_lookup_common(struct rpc_clnt **clnt, struct inode *dir,
-				   struct dentry *dentry, struct nfs_fh *fhandle,
-				   struct nfs_fattr *fattr)
+				   struct dentry *dentry, const struct qstr *name,
+				   struct nfs_fh *fhandle, struct nfs_fattr *fattr)
 {
 	struct nfs4_exception exception = {
 		.interruptible = true,
 	};
 	struct rpc_clnt *client = *clnt;
-	const struct qstr *name = &dentry->d_name;
 	int err;
 	do {
-		err = _nfs4_proc_lookup(client, dir, dentry, fhandle, fattr);
+		err = _nfs4_proc_lookup(client, dir, dentry, name, fhandle, fattr);
 		trace_nfs4_lookup(dir, name, err);
 		switch (err) {
 		case -NFS4ERR_BADNAME:
@@ -4631,13 +4630,13 @@ out:
 	return err;
 }
 
-static int nfs4_proc_lookup(struct inode *dir, struct dentry *dentry,
+static int nfs4_proc_lookup(struct inode *dir, struct dentry *dentry, const struct qstr *name,
 			    struct nfs_fh *fhandle, struct nfs_fattr *fattr)
 {
 	int status;
 	struct rpc_clnt *client = NFS_CLIENT(dir);
 
-	status = nfs4_proc_lookup_common(&client, dir, dentry, fhandle, fattr);
+	status = nfs4_proc_lookup_common(&client, dir, dentry, name, fhandle, fattr);
 	if (client != NFS_CLIENT(dir)) {
 		rpc_shutdown_client(client);
 		nfs_fixup_secinfo_attributes(fattr);
@@ -4652,7 +4651,8 @@ nfs4_proc_lookup_mountpoint(struct inode *dir, struct dentry *dentry,
 	struct rpc_clnt *client = NFS_CLIENT(dir);
 	int status;
 
-	status = nfs4_proc_lookup_common(&client, dir, dentry, fhandle, fattr);
+	status = nfs4_proc_lookup_common(&client, dir, dentry, &dentry->d_name,
+					 fhandle, fattr);
 	if (status < 0)
 		return ERR_PTR(status);
 	return (client == NFS_CLIENT(dir)) ? rpc_clone_client(client) : client;