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bpf: fix states equal logic for varlen access

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If we have a branch that looks something like this

int foo = map->value;
if (condition) {
  foo += blah;
} else {
  foo = bar;
}
map->array[foo] = baz;

We will incorrectly assume that the !condition branch is equal to the condition
branch as the register for foo will be UNKNOWN_VALUE in both cases.  We need to
adjust this logic to only do this if we didn't do a varlen access after we
processed the !condition branch, otherwise we have different ranges and need to
check the other branch as well.

Fixes: 484611357c ("bpf: allow access into map value arrays")
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Josef Bacik 2016-11-29 12:27:09 -05:00 committed by David S. Miller
parent 0fcba2894c
commit e2d2afe15e
1 changed files with 8 additions and 2 deletions
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10
kernel/bpf/verifier.c
View file

@ -2454,6 +2454,7 @@ static bool states_equal(struct bpf_verifier_env *env,
struct bpf_verifier_state *old,
struct bpf_verifier_state *cur)
{
bool varlen_map_access = env->varlen_map_value_access;
struct bpf_reg_state *rold, *rcur;
int i;
@ -2467,12 +2468,17 @@ static bool states_equal(struct bpf_verifier_env *env,
/* If the ranges were not the same, but everything else was and
* we didn't do a variable access into a map then we are a-ok.
*/
if (!env->varlen_map_value_access &&
if (!varlen_map_access &&
rold->type == rcur->type && rold->imm == rcur->imm)
continue;
/* 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.
*/
if (rold->type == NOT_INIT ||
(rold->type == UNKNOWN_VALUE && rcur->type != NOT_INIT))
(!varlen_map_access && rold->type == UNKNOWN_VALUE &&
rcur->type != NOT_INIT))
continue;
if (rold->type == PTR_TO_PACKET && rcur->type == PTR_TO_PACKET &&