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.
Signed-off-by: Josef Bacik <jba...@fb.com>
---
kernel/bpf/verifier.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 89f787c..2c8a688 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2478,6 +2478,7 @@ static bool states_equal(struct bpf_verifier_env *env,
{
struct bpf_reg_state *rold, *rcur;
int i;
+ bool map_access = env->varlen_map_value_access;
for (i = 0; i < MAX_BPF_REG; i++) {
rold = &old->regs[i];
@@ -2489,12 +2490,17 @@ 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 (!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))
+ (!map_access && (rold->type == UNKNOWN_VALUE &&
+ rcur->type != NOT_INIT)))
continue;
if (rold->type == PTR_TO_PACKET && rcur->type == PTR_TO_PACKET
&&
--
2.7.4
