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Message-Id: <20201019152331.20583-3-laniel_francis@privacyrequired.com> Date: Mon, 19 Oct 2020 17:23:30 +0200 From: laniel_francis@...vacyrequired.com To: linux-hardening@...r.kernel.org Cc: kuba@...nel.org, davem@...emloft.net, Francis Laniel <laniel_francis@...vacyrequired.com> Subject: [RFC][PATCH v2 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> --- include/net/netlink.h | 2 +- include/net/pkt_cls.h | 3 ++- lib/nlattr.c | 33 +++++++++++++++++++++------------ net/sched/act_api.c | 2 +- net/sched/cls_api.c | 2 +- net/sched/sch_api.c | 2 +- 6 files changed, 27 insertions(+), 17 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..85f4ac779399 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) < 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..d692716bda78 100644 --- a/lib/nlattr.c +++ b/lib/nlattr.c @@ -713,30 +713,39 @@ 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. + * Unlike strlcpy the destination buffer is always padded out. */ -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); - /* 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 41a55c6cbeb8..f0bf64393cbf 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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