bpf: Add bpf_dynptr_is_null and bpf_dynptr_is_rdonly

bpf_dynptr_is_null returns true if the dynptr is null / invalid
(determined by whether ptr->data is NULL), else false if
the dynptr is a valid dynptr.

bpf_dynptr_is_rdonly returns true if the dynptr is read-only,
else false if the dynptr is read-writable. If the dynptr is
null / invalid, false is returned by default.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20230420071414.570108-3-joannelkoong@gmail.com

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 42e06d1b492dcb042b530198959e72aacf4fd622..a683b3e71a2815c1f20504f665d298464a5f1b19 100644 (file)
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1423,7 +1423,7 @@ static const struct bpf_func_proto bpf_kptr_xchg_proto = {
 #define DYNPTR_SIZE_MASK       0xFFFFFF
 #define DYNPTR_RDONLY_BIT      BIT(31)
 
-static bool bpf_dynptr_is_rdonly(const struct bpf_dynptr_kern *ptr)
+static bool __bpf_dynptr_is_rdonly(const struct bpf_dynptr_kern *ptr)
 {
        return ptr->size & DYNPTR_RDONLY_BIT;
 }
@@ -1570,7 +1570,7 @@ BPF_CALL_5(bpf_dynptr_write, const struct bpf_dynptr_kern *, dst, u32, offset, v
        enum bpf_dynptr_type type;
        int err;
 
-       if (!dst->data || bpf_dynptr_is_rdonly(dst))
+       if (!dst->data || __bpf_dynptr_is_rdonly(dst))
                return -EINVAL;
 
        err = bpf_dynptr_check_off_len(dst, offset, len);
@@ -1626,7 +1626,7 @@ BPF_CALL_3(bpf_dynptr_data, const struct bpf_dynptr_kern *, ptr, u32, offset, u3
        if (err)
                return 0;
 
-       if (bpf_dynptr_is_rdonly(ptr))
+       if (__bpf_dynptr_is_rdonly(ptr))
                return 0;
 
        type = bpf_dynptr_get_type(ptr);
@@ -2276,7 +2276,7 @@ __bpf_kfunc void *bpf_dynptr_slice(const struct bpf_dynptr_kern *ptr, u32 offset
 __bpf_kfunc void *bpf_dynptr_slice_rdwr(const struct bpf_dynptr_kern *ptr, u32 offset,
                                        void *buffer, u32 buffer__szk)
 {
-       if (!ptr->data || bpf_dynptr_is_rdonly(ptr))
+       if (!ptr->data || __bpf_dynptr_is_rdonly(ptr))
                return NULL;
 
        /* bpf_dynptr_slice_rdwr is the same logic as bpf_dynptr_slice.
@@ -2322,6 +2322,19 @@ __bpf_kfunc int bpf_dynptr_adjust(struct bpf_dynptr_kern *ptr, u32 start, u32 en
        return 0;
 }
 
+__bpf_kfunc bool bpf_dynptr_is_null(struct bpf_dynptr_kern *ptr)
+{
+       return !ptr->data;
+}
+
+__bpf_kfunc bool bpf_dynptr_is_rdonly(struct bpf_dynptr_kern *ptr)
+{
+       if (!ptr->data)
+               return false;
+
+       return __bpf_dynptr_is_rdonly(ptr);
+}
+
 __bpf_kfunc void *bpf_cast_to_kern_ctx(void *obj)
 {
        return obj;
@@ -2395,6 +2408,8 @@ BTF_ID_FLAGS(func, bpf_iter_num_new, KF_ITER_NEW)
 BTF_ID_FLAGS(func, bpf_iter_num_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_num_destroy, KF_ITER_DESTROY)
 BTF_ID_FLAGS(func, bpf_dynptr_adjust)
+BTF_ID_FLAGS(func, bpf_dynptr_is_null)
+BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
 BTF_SET8_END(common_btf_ids)
 
 static const struct btf_kfunc_id_set common_kfunc_set = {