tools: ynl-gen: validate 0 len strings from kernel

Strings from the kernel are guaranteed to be null terminated and
ynl_attr_validate() checks for this. But it doesn't check if the string
has a len of 0, which would cause problems when trying to access
data[len - 1]. Fix this by checking that len is positive.

Signed-off-by: David Wei <dw@davidwei.uk>
Link: https://patch.msgid.link/20250503043050.861238-1-dw@davidwei.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/tools/net/ynl/lib/ynl.c b/tools/net/ynl/lib/ynl.c
index ce32cb35007d6f57ee55b4cff5afcac93c0e3d37..c4da34048ef8589d08cb02aa9674881761943abf 100644 (file)
--- a/tools/net/ynl/lib/ynl.c
+++ b/tools/net/ynl/lib/ynl.c
@@ -364,7 +364,7 @@ int ynl_attr_validate(struct ynl_parse_arg *yarg, const struct nlattr *attr)
                     "Invalid attribute (binary %s)", policy->name);
                return -1;
        case YNL_PT_NUL_STR:
-               if ((!policy->len || len <= policy->len) && !data[len - 1])
+               if (len && (!policy->len || len <= policy->len) && !data[len - 1])
                        break;
                yerr(yarg->ys, YNL_ERROR_ATTR_INVALID,
                     "Invalid attribute (string %s)", policy->name);