libkmod: consider empty signature key as invalid

A segmentation fault occurs if a module has an empty key attached to
its signature. This is mostly likely due to a corrupted module.

The crash happens because kmod_module_get_info() assumes that
kmod_module_signature_info() returns a signature of at least 1 byte.

The fix is based on a patch from Tobias Stoeckmann
<tobias@stoeckmann.org>, but rather than changing kmod_module_get_info()
to fix the crash, this changes kmod_module_signature_info() to
consider the signature as invalid.

diff --git a/libkmod/libkmod-signature.c b/libkmod/libkmod-signature.c
index 2260cc6214c28c664b1663faca4b53e53fceb3ae..5577305c1081b2371c81189817d0ce46852b150a 100644 (file)
--- a/libkmod/libkmod-signature.c
+++ b/libkmod/libkmod-signature.c
@@ -124,7 +124,8 @@ bool kmod_module_signature_info(const struct kmod_file *file, struct kmod_signat
                        modsig->id_type >= PKEY_ID_TYPE__LAST)
                return false;
        sig_len = be32toh(get_unaligned(&modsig->sig_len));
-       if (size < (int64_t)(modsig->signer_len + modsig->key_id_len + sig_len))
+       if (sig_len == 0 ||
+           size < (int64_t)(modsig->signer_len + modsig->key_id_len + sig_len))
                return false;
 
        size -= modsig->key_id_len + sig_len;