[PATCH bpf v4 3/4] bpf: Propagate untrusted pointer state in commuted arithmetic

The untrusted PTR_TO_MEM early return skips pointer offset tracking
because accesses go through probe-read handling. Moving it after full
pointer-state propagation ensures scalar += untrusted_pointer leaves the
destination as PTR_TO_MEM instead of an unrelated scalar.

Fixes: f2362a57aeff ("bpf: allow void* cast using bpf_rdonly_cast()")
Tested-by: Daniel Wade <[email protected]>
Signed-off-by: Yiyang Chen <[email protected]>
---
 kernel/bpf/verifier.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index cdb61fab84351..fdc5fbb1f78ca 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -13707,13 +13707,6 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
 		return -EACCES;
 	}
 
-	/*
-	 * Accesses to untrusted PTR_TO_MEM are done through probe
-	 * instructions, hence no need to track offsets.
-	 */
-	if (base_type(ptr_reg->type) == PTR_TO_MEM && (ptr_reg->type & PTR_UNTRUSTED))
-		return 0;
-
 	switch (base_type(ptr_reg->type)) {
 	case PTR_TO_CTX:
 	case PTR_TO_MAP_VALUE:
@@ -13750,6 +13743,13 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
 	if (dst_reg != ptr_reg)
 		*dst_reg = *ptr_reg;
 
+	/*
+	 * Accesses to untrusted PTR_TO_MEM are done through probe
+	 * instructions, hence no need to track offsets.
+	 */
+	if (base_type(ptr_reg->type) == PTR_TO_MEM && (ptr_reg->type & PTR_UNTRUSTED))
+		return 0;
+
 	if (!check_reg_sane_offset_scalar(env, off_reg, ptr_reg->type) ||
 	    !check_reg_sane_offset_ptr(env, ptr_reg, ptr_reg->type))
 		return -EINVAL;

-- 
2.43.0