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Message-Id: <20201030153647.4408-3-laniel_francis@privacyrequired.com>
Date: Fri, 30 Oct 2020 16:36:46 +0100
From: laniel_francis@...vacyrequired.com
To: linux-hardening@...r.kernel.org, netdev@...r.kernel.org
Cc: davem@...emloft.net, kuba@...nel.org, keescook@...omium.org,
Francis Laniel <laniel_francis@...vacyrequired.com>
Subject: [PATCH v4 2/3] Modify return value of nla_strlcpy to match that of strscpy.
From: Francis Laniel <laniel_francis@...vacyrequired.com>
nla_strlcpy now returns -E2BIG if src was truncated when written to dst.
It also returns this error value if dstsize is 0 or higher than INT_MAX.
For example, if src is "foo\0" and dst is 3 bytes long, the result will be:
1. "foG" after memcpy (G means garbage).
2. "fo\0" after memset.
3. -E2BIG is returned because src was not completely written into dst.
The callers of nla_strlcpy were modified to take into account this modification.
Signed-off-by: Francis Laniel <laniel_francis@...vacyrequired.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
---
include/net/netlink.h | 2 +-
include/net/pkt_cls.h | 2 +-
lib/nlattr.c | 39 +++++++++++++++++++++++++--------------
net/sched/act_api.c | 2 +-
net/sched/cls_api.c | 2 +-
net/sched/sch_api.c | 2 +-
6 files changed, 30 insertions(+), 19 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..db9a828f4f4f 100644
--- a/include/net/pkt_cls.h
+++ b/include/net/pkt_cls.h
@@ -512,7 +512,7 @@ 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) < 0) {
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 07156e581997..447182543c03 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -710,33 +710,44 @@ EXPORT_SYMBOL(nla_find);
/**
* nla_strlcpy - Copy string attribute payload into a sized buffer
- * @dst: where to copy the string to
- * @nla: attribute to copy the string from
- * @dstsize: size of destination buffer
+ * @dst: Where to copy the string to.
+ * @nla: Attribute to copy the string from.
+ * @dstsize: Size of destination buffer.
*
* 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.
+ * Unlike strlcpy the destination buffer is always padded out.
*
- * Returns the length of the source buffer.
+ * Return:
+ * * srclen - Returns @nla length (not including the trailing %NUL).
+ * * -E2BIG - If @dstsize is 0 or greater than U16_MAX or @nla length greater
+ * than @dstsize.
*/
-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 srclen = nla_len(nla);
char *src = nla_data(nla);
+ ssize_t ret;
+ size_t len;
+
+ if (dstsize == 0 || WARN_ON_ONCE(dstsize > U16_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);
- /* Zero pad end of dst. */
- memset(dst + len, 0, dstsize - len);
+ if (srclen >= dstsize) {
+ len = dstsize - 1;
+ ret = -E2BIG;
+ } else {
+ len = srclen;
+ ret = len;
}
- return srclen;
+ memcpy(dst, src, len);
+ /* Zero pad end of dst. */
+ memset(dst + len, 0, dstsize - len);
+
+ return ret;
}
EXPORT_SYMBOL(nla_strlcpy);
diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index f66417d5d2c3..541574520c52 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) < 0) {
NL_SET_ERR_MSG(extack, "TC action name too long");
goto err_out;
}
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 838b3fd94d77..d3787a67b3da 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -223,7 +223,7 @@ static inline u32 tcf_auto_prio(struct tcf_proto *tp)
static bool tcf_proto_check_kind(struct nlattr *kind, char *name)
{
if (kind)
- return nla_strlcpy(name, kind, IFNAMSIZ) >= IFNAMSIZ;
+ return nla_strlcpy(name, kind, IFNAMSIZ) < 0;
memset(name, 0, IFNAMSIZ);
return false;
}
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 2a76a2f5ed88..f9b053b30a7b 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) > 0) {
/* 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
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