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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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