linux-hardening - [PATCH v1 2/3] Modify return value of nla

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Date:   Fri, 16 Oct 2020 14:52:15 +0200
From:   laniel_francis@...vacyrequired.com
To:     linux-hardening@...r.kernel.org
Cc:     Francis Laniel <laniel_francis@...vacyrequired.com>
Subject: [PATCH v1 2/3] Modify return value of nla_strlcpy to match that of strscpy.

From: Francis Laniel <laniel_francis@...vacyrequired.com>

This patch solves part 2 of issue: https://github.com/KSPP/linux/issues/110

Signed-off-by: Francis Laniel <laniel_francis@...vacyrequired.com>
---
 include/net/netlink.h |  2 +-
 include/net/pkt_cls.h |  3 ++-
 lib/nlattr.c          | 31 ++++++++++++++++++++-----------
 net/sched/act_api.c   |  2 +-
 net/sched/sch_api.c   |  2 +-
 5 files changed, 25 insertions(+), 15 deletions(-)

diff --git a/include/net/netlink.h b/include/net/netlink.h
index 7356f41d23ba..446ca182e13d 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -506,7 +506,7 @@ int __nla_parse(struct nlattr **tb, int maxtype, const struct nlattr *head,
 		struct netlink_ext_ack *extack);
 int nla_policy_len(const struct nla_policy *, int);
 struct nlattr *nla_find(const struct nlattr *head, int len, int attrtype);
-size_t nla_strlcpy(char *dst, const struct nlattr *nla, size_t dstsize);
+ssize_t nla_strlcpy(char *dst, const struct nlattr *nla, size_t dstsize);
 char *nla_strdup(const struct nlattr *nla, gfp_t flags);
 int nla_memcpy(void *dest, const struct nlattr *src, int count);
 int nla_memcmp(const struct nlattr *nla, const void *data, size_t size);
diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
index d4d461236351..f42db07c399b 100644
--- a/include/net/pkt_cls.h
+++ b/include/net/pkt_cls.h
@@ -4,6 +4,7 @@
 
 #include <linux/pkt_cls.h>
 #include <linux/workqueue.h>
+#include <linux/errno.h>
 #include <net/sch_generic.h>
 #include <net/act_api.h>
 #include <net/net_namespace.h>
@@ -512,7 +513,7 @@ tcf_change_indev(struct net *net, struct nlattr *indev_tlv,
 	char indev[IFNAMSIZ];
 	struct net_device *dev;
 
-	if (nla_strlcpy(indev, indev_tlv, IFNAMSIZ) >= IFNAMSIZ) {
+	if (nla_strlcpy(indev, indev_tlv, IFNAMSIZ) == -E2BIG) {
 		NL_SET_ERR_MSG_ATTR(extack, indev_tlv,
 				    "Interface name too long");
 		return -EINVAL;
diff --git a/lib/nlattr.c b/lib/nlattr.c
index ab96a5f4b9b8..83dd233bbe3e 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -713,29 +713,38 @@ EXPORT_SYMBOL(nla_find);
  * @dst: where to copy the string to
  * @nla: attribute to copy the string from
  * @dstsize: size of destination buffer
+ * @returns: -E2BIG if @dstsize is 0 or source buffer length greater than
+ * @dstsize, otherwise it returns the number of copied characters (not
+ * including the trailing %NUL).
  *
  * Copies at most dstsize - 1 bytes into the destination buffer.
- * The result is always a valid NUL-terminated string. Unlike
- * strlcpy the destination buffer is always padded out.
- *
- * Returns the length of the source buffer.
+ * The result is always a valid NUL-terminated string.
  */
-size_t nla_strlcpy(char *dst, const struct nlattr *nla, size_t dstsize)
+ssize_t nla_strlcpy(char *dst, const struct nlattr *nla, size_t dstsize)
 {
+	size_t len;
+	ssize_t ret;
 	size_t srclen = nla_len(nla);
 	char *src = nla_data(nla);
 
+	if (dstsize == 0 || WARN_ON_ONCE(dstsize > INT_MAX))
+		return -E2BIG;
+
 	if (srclen > 0 && src[srclen - 1] == '\0')
 		srclen--;
 
-	if (dstsize > 0) {
-		size_t len = (srclen >= dstsize) ? dstsize - 1 : srclen;
-
-		memcpy(dst, src, len);
-		dst[len] = '\0';
+	if (srclen >= dstsize) {
+		len = dstsize - 1;
+		ret = -E2BIG;
+	} else {
+		len = srclen;
+		ret = len;
 	}
 
-	return srclen;
+	memcpy(dst, src, len);
+	dst[len] = '\0';
+
+	return ret;
 }
 EXPORT_SYMBOL(nla_strlcpy);
 
diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index f66417d5d2c3..ed411d6c29fc 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -935,7 +935,7 @@ struct tc_action *tcf_action_init_1(struct net *net, struct tcf_proto *tp,
 			NL_SET_ERR_MSG(extack, "TC action kind must be specified");
 			goto err_out;
 		}
-		if (nla_strlcpy(act_name, kind, IFNAMSIZ) >= IFNAMSIZ) {
+		if (nla_strlcpy(act_name, kind, IFNAMSIZ) == -E2BIG) {
 			NL_SET_ERR_MSG(extack, "TC action name too long");
 			goto err_out;
 		}
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 2a76a2f5ed88..3e89c666d1e8 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1170,7 +1170,7 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
 #ifdef CONFIG_MODULES
 	if (ops == NULL && kind != NULL) {
 		char name[IFNAMSIZ];
-		if (nla_strlcpy(name, kind, IFNAMSIZ) < IFNAMSIZ) {
+		if (nla_strlcpy(name, kind, IFNAMSIZ) != -E2BIG) {
 			/* We dropped the RTNL semaphore in order to
 			 * perform the module load.  So, even if we
 			 * succeeded in loading the module we have to
-- 
2.20.1