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Message-ID: <202010161620.3B240DBCC1@keescook> 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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