[PATCH v1] bpf: Add length check for SK_DIAG_BPF_STORAGE_REQ_MAP_FD parsing

[Lin Ma]

The nla_for_each_nested parsing in function bpf_sk_storage_diag_alloc
does not check the length of the nested attribute. This can lead to an
out-of-attribute read and allow a malformed nlattr (e.g., length 0) to
be viewed as a 4 byte integer.

This patch adds additional check before the execution of nla_get_u32 to
make sure the attribute has enough length.

Fixes: 1ed4d92458a9 ("bpf: INET_DIAG support in bpf_sk_storage")
Signed-off-by: Lin Ma <linma@xxxxxxxxxx>
---
 net/core/bpf_sk_storage.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
index d4172534dfa8..6f1afbb394a6 100644
--- a/net/core/bpf_sk_storage.c
+++ b/net/core/bpf_sk_storage.c
@@ -511,6 +511,11 @@ bpf_sk_storage_diag_alloc(const struct nlattr *nla_stgs)
 		if (nla_type(nla) != SK_DIAG_BPF_STORAGE_REQ_MAP_FD)
 			continue;
 
+		if (nla_len(nla) < sizeof(map_fd)) {
+			err = -EINVAL;
+			goto err_free;
+		}
+
 		map_fd = nla_get_u32(nla);
 		map = bpf_map_get(map_fd);
 		if (IS_ERR(map)) {
-- 
2.17.1