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bpf/verifier: Fix states_equal() comparison of pointer and UNKNOWN

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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 f1174f77b5 "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>
Cc: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Ben Hutchings 2017-12-23 02:26:17 +00:00 committed by Greg Kroah-Hartman
parent 69cf72b287
commit 37435f7e80
1 changed files with 3 additions and 2 deletions
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5
kernel/bpf/verifier.c
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@ -2722,11 +2722,12 @@ static bool states_equal(struct bpf_verifier_env *env,
/* 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. */