linux-kernel - Re: [PATCH] PKCS#7: pkcs7_validate_trust(): initialize the

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Date:	Wed, 23 Mar 2016 20:59:12 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Nicolai Stange <nicstange@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	David Howells <dhowells@...hat.com>,
	Tadeusz Struk <tadeusz.struk@...el.com>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PKCS#7: pkcs7_validate_trust(): initialize the _trusted
 output argument

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@...il.com>

Patch applied.  Thanks!
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt