Re: [PATCH] PKCS#7: pkcs7_validate_trust(): initialize the _trusted output argument
From: Nicolai Stange
Date: Wed Mar 23 2016 - 10:00:32 EST
Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> writes:
> On Sun, Mar 20, 2016 at 11:23:46PM +0100, Nicolai Stange wrote:
>> Despite what the DocBook comment to pkcs7_validate_trust() says, the
>> *_trusted argument is never set to false.
>>
>> pkcs7_validate_trust() only positively sets *_trusted upon encountering
>> a trusted PKCS#7 SignedInfo block.
>>
>> This is quite unfortunate since its callers, system_verify_data() for
>> example, depend on pkcs7_validate_trust() clearing *_trusted on non-trust.
>>
>> Indeed, UBSAN splats when attempting to load the uninitialized local
>> variable 'trusted' from system_verify_data() in pkcs7_validate_trust():
>>
>> UBSAN: Undefined behaviour in crypto/asymmetric_keys/pkcs7_trust.c:194:14
>> load of value 82 is not a valid value for type '_Bool'
>> [...]
>> Call Trace:
>> [<ffffffff818c4d35>] dump_stack+0xbc/0x117
>> [<ffffffff818c4c79>] ? _atomic_dec_and_lock+0x169/0x169
>> [<ffffffff8194113b>] ubsan_epilogue+0xd/0x4e
>> [<ffffffff819419fa>] __ubsan_handle_load_invalid_value+0x111/0x158
>> [<ffffffff819418e9>] ? val_to_string.constprop.12+0xcf/0xcf
>> [<ffffffff818334a4>] ? x509_request_asymmetric_key+0x114/0x370
>> [<ffffffff814b83f0>] ? kfree+0x220/0x370
>> [<ffffffff818312c2>] ? public_key_verify_signature_2+0x32/0x50
>> [<ffffffff81835e04>] pkcs7_validate_trust+0x524/0x5f0
>> [<ffffffff813c391a>] system_verify_data+0xca/0x170
>> [<ffffffff813c3850>] ? top_trace_array+0x9b/0x9b
>> [<ffffffff81510b29>] ? __vfs_read+0x279/0x3d0
>> [<ffffffff8129372f>] mod_verify_sig+0x1ff/0x290
>> [...]
>>
>> The implication is that pkcs7_validate_trust() effectively grants trust
>> when it really shouldn't have.
>>
>> Fix this by explicitly setting *_trusted to false at the very beginning
>> of pkcs7_validate_trust().
>>
>> Signed-off-by: Nicolai Stange <nicstange@xxxxxxxxx>
>
> Patch applied. Thanks!
Thank you very much!