From: Ben Hutchings <ben@decadent.org.uk>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: stable@vger.kernel.org, netdev@vger.kernel.org,
Edward Cree <ecree@solarflare.com>, Jann Horn <jannh@google.com>,
Alexei Starovoitov <ast@kernel.org>
Subject: [PATCH 4.9] bpf/verifier: Fix states_equal() comparison of pointer and UNKNOWN
Date: Sat, 23 Dec 2017 02:26:17 +0000 [thread overview]
Message-ID: <20171223022617.GO2971@decadent.org.uk> (raw)
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An UNKNOWN_VALUE is not supposed to be derived from a pointer, unless
pointer leaks are allowed. Therefore, states_equal() must not treat
a state with a pointer in a register as "equal" to a state with an
UNKNOWN_VALUE in that register.
This was fixed differently upstream, but the code around here was
largely rewritten in 4.14 by commit f1174f77b50c "bpf/verifier: rework
value tracking". The bug can be detected by the bpf/verifier sub-test
"pointer/scalar confusion in state equality check (way 1)".
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Edward Cree <ecree@solarflare.com>
Cc: Jann Horn <jannh@google.com>
Cc: Alexei Starovoitov <ast@kernel.org>
---
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2722,11 +2722,12 @@ static bool states_equal(struct bpf_veri
/* If we didn't map access then again we don't care about the
* mismatched range values and it's ok if our old type was
- * UNKNOWN and we didn't go to a NOT_INIT'ed reg.
+ * UNKNOWN and we didn't go to a NOT_INIT'ed or pointer reg.
*/
if (rold->type == NOT_INIT ||
(!varlen_map_access && rold->type == UNKNOWN_VALUE &&
- rcur->type != NOT_INIT))
+ rcur->type != NOT_INIT &&
+ !__is_pointer_value(env->allow_ptr_leaks, rcur)))
continue;
/* Don't care about the reg->id in this case. */
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next reply other threads:[~2017-12-23 2:26 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-23 2:26 Ben Hutchings [this message]
2017-12-23 3:51 ` [PATCH 4.9] bpf/verifier: Fix states_equal() comparison of pointer and UNKNOWN Alexei Starovoitov
2017-12-27 20:04 ` Patch "bpf/verifier: Fix states_equal() comparison of pointer and UNKNOWN" has been added to the 4.9-stable tree gregkh
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