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>
---
Applicable to linux-next-20160318
crypto/asymmetric_keys/pkcs7_trust.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/crypto/asymmetric_keys/pkcs7_trust.c b/crypto/asymmetric_keys/pkcs7_trust.c
index 3bbdcc7..7d7a39b4 100644
--- a/crypto/asymmetric_keys/pkcs7_trust.c
+++ b/crypto/asymmetric_keys/pkcs7_trust.c
@@ -178,6 +178,8 @@ int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
int cached_ret = -ENOKEY;
int ret;
+ *_trusted = false;
+
for (p = pkcs7->certs; p; p = p->next)
p->seen = false;
--
2.7.3
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