Hi, if kmod has been configured with --disable-largefile on a 32 bit system, off_t will be 32 bit. In that case, the parsed sig_len can bypass a validation check (it's _unsigned_ 32 bit), allowing a an attacker to perform out of boundary access through a malicious module. Due to the unlikeliness of people using --disable-largefile, this is a mere validation fix. With an explicit signed 64 bit cast, there is no binary change for 99.9% of Linux systems out there. ;) Attached please find a proof of concept, which will most likely result in a segmentation fault (works fine with 64 bit off_t builds): tobias:~$ modinfo 32sig.ko filename: /home/tobias/32sig.ko Segmentation fault Tobias --- libkmod/libkmod-signature.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/libkmod/libkmod-signature.c b/libkmod/libkmod-signature.c index 5ed5973..bced8ab 100644 --- a/libkmod/libkmod-signature.c +++ b/libkmod/libkmod-signature.c @@ -124,7 +124,7 @@ 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 < (off_t)(modsig->signer_len + modsig->key_id_len + sig_len)) + if (size < (int64_t)(modsig->signer_len + modsig->key_id_len + sig_len)) return false; size -= modsig->key_id_len + sig_len; -- 2.3.0
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32sig.ko
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