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Date: Fri, 16 Oct 2020 16:23:10 -0700
From: Kees Cook <keescook@...omium.org>
To: laniel_francis@...vacyrequired.com
Cc: linux-hardening@...r.kernel.org
Subject: Re: [PATCH v1 2/3] Modify return value of nla_strlcpy to match that
of strscpy.
On Fri, Oct 16, 2020 at 02:52:15PM +0200, laniel_francis@...vacyrequired.com wrote:
> From: Francis Laniel <laniel_francis@...vacyrequired.com>
>
> This patch solves part 2 of issue: https://github.com/KSPP/linux/issues/110
As with the others, this needs a full commit log (imagine someone
doesn't have access to read that issue, etc).
>
> 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) {
I would make these tests all be "< 0" rather than specifically -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;
Cool, yeah, good to include.
> +
> 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);
Otherwise, I think this looks good. (Though same note about
zero-padding.)
>
> 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
>
--
Kees Cook
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