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Message-ID: <4277076.SKpFQfNsve@machine> Date: Sat, 17 Oct 2020 10:53:20 +0200 From: Francis Laniel <laniel_francis@...vacyrequired.com> To: Kees Cook <keescook@...omium.org> Cc: linux-hardening@...r.kernel.org Subject: Re: [PATCH v1 2/3] Modify return value of nla_strlcpy to match that of strscpy. Le samedi 17 octobre 2020, 01:23:10 CEST Kees Cook a écrit : > 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). I will reexplain the whole problem into the commit message to give more context to it in the next version. > > > 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. > You are right, it would permit to add more -ESOMETHING to nla_sltrcpy without changing the caller each time. > > 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. > Thank you! > > + > > > > 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
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