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    SubjectRe: [PATCH v4 10/10] nl80211: sanitize array index in parse_txq_params
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    On Thu, 2018-01-18 at 16:02 -0800, Dan Williams wrote:
    > Wireless drivers rely on parse_txq_params to validate that
    > txq_params->ac is less than NL80211_NUM_ACS by the time the low-level
    > driver's ->conf_tx() handler is called. Use a new helper, 'array_idx',
    > to sanitize txq_params->ac with respect to speculation. I.e. ensure that
    > any speculation into ->conf_tx() handlers is done with a value of
    > txq_params->ac that is within the bounds of [0, NL80211_NUM_ACS).

    Sorry, I didn't realize you were waiting for me to review.

    LGTM.

    Reviewed-by: Johannes Berg <johannes@sipsolutions.net>


    > Reported-by: Christian Lamparter <chunkeey@gmail.com>
    > Reported-by: Elena Reshetova <elena.reshetova@intel.com>
    > Cc: Johannes Berg <johannes@sipsolutions.net>
    > Cc: "David S. Miller" <davem@davemloft.net>
    > Cc: linux-wireless@vger.kernel.org
    > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
    > ---
    > include/linux/nospec.h | 21 +++++++++++++++++++++
    > net/wireless/nl80211.c | 10 +++++++---
    > 2 files changed, 28 insertions(+), 3 deletions(-)
    >
    > diff --git a/include/linux/nospec.h b/include/linux/nospec.h
    > index f841c11f3f1f..8af35be1869e 100644
    > --- a/include/linux/nospec.h
    > +++ b/include/linux/nospec.h
    > @@ -41,4 +41,25 @@ static inline unsigned long array_ptr_mask(unsigned long idx, unsigned long sz)
    > __u._bit &= _mask; \
    > __u._ptr; \
    > })
    > +
    > +/**
    > + * array_idx - Generate a pointer to an array index, ensuring the
    > + * pointer is bounded under speculation to NULL.
    > + *
    > + * @idx: the index of the element, must be less than LONG_MAX
    > + * @sz: the number of elements in the array, must be less than LONG_MAX
    > + *
    > + * If @idx falls in the interval [0, @sz), returns &@idx otherwise
    > + * returns NULL.
    > + */
    > +#define array_idx(idx, sz) \
    > +({ \
    > + union { typeof((idx)) *_ptr; unsigned long _bit; } __u; \
    > + typeof(idx) *_i = &(idx); \
    > + unsigned long _mask = array_ptr_mask(*_i, (sz)); \
    > + \
    > + __u._ptr = _i; \
    > + __u._bit &= _mask; \
    > + __u._ptr; \
    > +})
    > #endif /* __NOSPEC_H__ */
    > diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
    > index 2b3dbcd40e46..202cb1dc03ee 100644
    > --- a/net/wireless/nl80211.c
    > +++ b/net/wireless/nl80211.c
    > @@ -16,6 +16,7 @@
    > #include <linux/nl80211.h>
    > #include <linux/rtnetlink.h>
    > #include <linux/netlink.h>
    > +#include <linux/nospec.h>
    > #include <linux/etherdevice.h>
    > #include <net/net_namespace.h>
    > #include <net/genetlink.h>
    > @@ -2056,20 +2057,23 @@ static const struct nla_policy txq_params_policy[NL80211_TXQ_ATTR_MAX + 1] = {
    > static int parse_txq_params(struct nlattr *tb[],
    > struct ieee80211_txq_params *txq_params)
    > {
    > + u8 ac, *idx;
    > +
    > if (!tb[NL80211_TXQ_ATTR_AC] || !tb[NL80211_TXQ_ATTR_TXOP] ||
    > !tb[NL80211_TXQ_ATTR_CWMIN] || !tb[NL80211_TXQ_ATTR_CWMAX] ||
    > !tb[NL80211_TXQ_ATTR_AIFS])
    > return -EINVAL;
    >
    > - txq_params->ac = nla_get_u8(tb[NL80211_TXQ_ATTR_AC]);
    > + ac = nla_get_u8(tb[NL80211_TXQ_ATTR_AC]);
    > txq_params->txop = nla_get_u16(tb[NL80211_TXQ_ATTR_TXOP]);
    > txq_params->cwmin = nla_get_u16(tb[NL80211_TXQ_ATTR_CWMIN]);
    > txq_params->cwmax = nla_get_u16(tb[NL80211_TXQ_ATTR_CWMAX]);
    > txq_params->aifs = nla_get_u8(tb[NL80211_TXQ_ATTR_AIFS]);
    >
    > - if (txq_params->ac >= NL80211_NUM_ACS)
    > + idx = array_idx(ac, NL80211_NUM_ACS);
    > + if (!idx)
    > return -EINVAL;
    > -
    > + txq_params->ac = *idx;
    > return 0;
    > }
    >
    >
    >

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