NFS: reject request for id_legacy key without auxdata

commit 49686cbbb3ebafe42e63868222f269d8053ead00 upstream.

nfs_idmap_legacy_upcall() is supposed to be called with 'aux' pointing
to a 'struct idmap', via the call to request_key_with_auxdata() in
nfs_idmap_request_key().

However it can also be reached via the request_key() system call in
which case 'aux' will be NULL, causing a NULL pointer dereference in
nfs_idmap_prepare_pipe_upcall(), assuming that the key description is
valid enough to get that far.

Fix this by making nfs_idmap_legacy_upcall() negate the key if no
auxdata is provided.

As usual, this bug was found by syzkaller.  A simple reproducer using
the command-line keyctl program is:

    keyctl request2 id_legacy uid:0 '' @s

Fixes: 57e62324e469 ("NFS: Store the legacy idmapper result in the keyring")
Reported-by: syzbot+5dfdbcf7b3eb5912abbb@syzkaller.appspotmail.com
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Trond Myklebust <trondmy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/nfs/nfs4idmap.c b/fs/nfs/nfs4idmap.c
index 30426c1..22dc30a 100644 (file)
--- a/fs/nfs/nfs4idmap.c
+++ b/fs/nfs/nfs4idmap.c
@@ -568,9 +568,13 @@ static int nfs_idmap_legacy_upcall(struct key_construction *cons,
        struct idmap_msg *im;
        struct idmap *idmap = (struct idmap *)aux;
        struct key *key = cons->key;
-       int ret = -ENOMEM;
+       int ret = -ENOKEY;
+
+       if (!aux)
+               goto out1;
 
        /* msg and im are freed in idmap_pipe_destroy_msg */
+       ret = -ENOMEM;
        data = kzalloc(sizeof(*data), GFP_KERNEL);
        if (!data)
                goto out1;