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Date:   Wed, 15 Jul 2020 15:00:01 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>, ast@...nel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Hangbin Liu <liuhangbin@...il.com>
Subject: [PATCH bpf-next] bpf: add a new bpf argument type ARG_CONST_MAP_PTR_OR_NULL

Add a new bpf argument type ARG_CONST_MAP_PTR_OR_NULL which could be
used when we want to allow NULL pointer for map parameter. The bpf helper
need to take care and check if the map is NULL when use this type.

Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
---
 include/linux/bpf.h   |  1 +
 kernel/bpf/verifier.c | 11 ++++++++---
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index c67c88ad35f8..9d4dbef3c943 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -253,6 +253,7 @@ enum bpf_arg_type {
 	ARG_PTR_TO_ALLOC_MEM,	/* pointer to dynamically allocated memory */
 	ARG_PTR_TO_ALLOC_MEM_OR_NULL,	/* pointer to dynamically allocated memory or NULL */
 	ARG_CONST_ALLOC_SIZE_OR_ZERO,	/* number of allocated bytes requested */
+	ARG_CONST_MAP_PTR_OR_NULL,	/* const argument used as pointer to bpf_map or NULL */
 };
 
 /* type of values returned from helper functions */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3c1efc9d08fd..d3551a19853a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3849,9 +3849,13 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 		expected_type = SCALAR_VALUE;
 		if (type != expected_type)
 			goto err_type;
-	} else if (arg_type == ARG_CONST_MAP_PTR) {
+	} else if (arg_type == ARG_CONST_MAP_PTR ||
+		   arg_type == ARG_CONST_MAP_PTR_OR_NULL) {
 		expected_type = CONST_PTR_TO_MAP;
-		if (type != expected_type)
+		if (register_is_null(reg) &&
+		    arg_type == ARG_CONST_MAP_PTR_OR_NULL)
+			/* final test in check_stack_boundary() */;
+		else if (type != expected_type)
 			goto err_type;
 	} else if (arg_type == ARG_PTR_TO_CTX ||
 		   arg_type == ARG_PTR_TO_CTX_OR_NULL) {
@@ -3957,7 +3961,8 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 		return -EFAULT;
 	}
 
-	if (arg_type == ARG_CONST_MAP_PTR) {
+	if (arg_type == ARG_CONST_MAP_PTR ||
+	    (arg_type == ARG_CONST_MAP_PTR_OR_NULL && !register_is_null(reg))) {
 		/* bpf_map_xxx(map_ptr) call: remember that map_ptr */
 		meta->map_ptr = reg->map_ptr;
 	} else if (arg_type == ARG_PTR_TO_MAP_KEY) {
-- 
2.25.4

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