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  1. Mar 23, 2016
    • Nicolai Stange's avatar
      PKCS#7: pkcs7_validate_trust(): initialize the _trusted output argument · e5435891
      Nicolai Stange authored
      
      
      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().
      
      Cc: <stable@vger.kernel.org>
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      e5435891
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