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Message-Id: <20180926200630.23399-1-johannes@sipsolutions.net>
Date: Wed, 26 Sep 2018 22:06:30 +0200
From: Johannes Berg <johannes@...solutions.net>
To: linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Cc: Johannes Berg <johannes.berg@...el.com>
Subject: [PATCH] netlink: add policy attribute range validation
From: Johannes Berg <johannes.berg@...el.com>
Without further bloating the policy structs, we can overload
the `validation_data' pointer with a struct of s16 min, max
and use those to validate ranges in NLA_{U,S}{8,16,32,64}
attributes.
It may sound strange to validate NLA_U32 with a s16 max, but
in many cases NLA_U32 is used for enums etc. since there's no
size benefit in using a smaller attribute width anyway, due
to netlink attribute alignment; in cases like that it's still
useful, particularly when the attribute really transports an
enum value.
Doing so lets us remove quite a bit of validation code, if we
can be sure that these attributes aren't used by userspace in
places where they're ignored today.
Signed-off-by: Johannes Berg <johannes.berg@...el.com>
---
include/net/netlink.h | 25 +++++++++++++++++++++++--
lib/nlattr.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 72 insertions(+), 2 deletions(-)
diff --git a/include/net/netlink.h b/include/net/netlink.h
index 3698ca8ff92c..ddabc832febc 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -238,7 +238,23 @@ enum {
* nested attributes directly inside, while an array has
* the nested attributes at another level down and the
* attributes directly in the nesting don't matter.
- * All other Unused
+ * All other Unused - but note that it's a union
+ *
+ * Meaning of `min' and `max' fields:
+ * NLA_U8,
+ * NLA_U16,
+ * NLA_U32,
+ * NLA_U64,
+ * NLA_S8,
+ * NLA_S16,
+ * NLA_S32,
+ * NLA_S64 If at least one of them is non-zero, they are the
+ * minimum and maximum value accepted for the attribute;
+ * note that in the interest of code simplicity and
+ * struct size both limits are s16, so you cannot
+ * enforce a range that doesn't fall within the range
+ * of s16 - do that as usual in the code instead.
+ * All other Unused - but note that it's a union
*
* Example:
* static const struct nla_policy my_policy[ATTR_MAX+1] = {
@@ -251,7 +267,12 @@ enum {
struct nla_policy {
u16 type;
u16 len;
- const void *validation_data;
+ union {
+ const void *validation_data;
+ struct {
+ s16 min, max;
+ };
+ };
};
#define NLA_POLICY_EXACT_LEN(_len) { .type = NLA_EXACT_LEN, .len = _len }
diff --git a/lib/nlattr.c b/lib/nlattr.c
index 2f8feff669a7..dd8d34c1ae19 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -230,6 +230,55 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
goto out_err;
}
+ /* validate range */
+ if (pt->min || pt->max) {
+ s64 value;
+ bool validate = true;
+
+ switch (pt->type) {
+ case NLA_U8:
+ value = nla_get_u8(nla);
+ break;
+ case NLA_U16:
+ value = nla_get_u16(nla);
+ break;
+ case NLA_U32:
+ value = nla_get_u32(nla);
+ break;
+ case NLA_S8:
+ value = nla_get_s8(nla);
+ break;
+ case NLA_S16:
+ value = nla_get_s16(nla);
+ break;
+ case NLA_S32:
+ value = nla_get_s32(nla);
+ break;
+ case NLA_S64:
+ value = nla_get_s64(nla);
+ break;
+ case NLA_U64:
+ /* treat this one specially, since it may not fit into s64 */
+ if (nla_get_u64(nla) < pt->min ||
+ nla_get_u64(nla) > pt->max) {
+ NL_SET_ERR_MSG_ATTR(extack, nla,
+ "integer out of range");
+ return -ERANGE;
+ }
+ /* fall through */
+ default:
+ /* no further validation */
+ validate = false;
+ break;
+ }
+
+ if (validate && (value < pt->min || value > pt->max)) {
+ NL_SET_ERR_MSG_ATTR(extack, nla,
+ "integer out of range");
+ return -ERANGE;
+ }
+ }
+
return 0;
out_err:
NL_SET_ERR_MSG_ATTR(extack, nla, "Attribute failed policy validation");
--
2.14.4
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