On 02/08/2012 06:14 PM, Daniel Halperin wrote: > On Wed, Feb 8, 2012 at 9:06 AM, Felix Fietkau <nbd@xxxxxxxxxxx<mailto:nbd@xxxxxxxxxxx>> wrote: > On 2012-02-08 5:27 PM, Arend van Spriel wrote: >> On 02/08/2012 05:08 PM, Felix Fietkau wrote: >>> On 2012-02-08 1:44 PM, Arend van Spriel wrote: >>>> This patch fixes the following NULL pointer dereference: >>>> >>>>> I rerun the test on a kernel with some more lock checking and got lucky. >>>>> >>>>> Feb 8 08:40:17 lb-bun-10 kernel: [ 514.512283] wlan0: authenticate >>>>> with 98:fc:11:8e:94:57 >>>>> Feb 8 08:40:17 lb-bun-10 kernel: [ 514.512515] wlan0: send auth to >>>>> 98:fc:11:8e:94:57 (try 1/3) >>>>> Feb 8 08:40:17 lb-bun-10 kernel: [ 514.514184] BUG: unable to handle >>>>> kernel NULL pointer dereference at 00000004 >>>>> Feb 8 08:40:17 lb-bun-10 kernel: [ 514.514233] IP: [<f8648f08>] >>>>> minstrel_tx_status+0x48/0xe0 [mac80211] >>>> >>>> static inline int >>>> rix_to_ndx(struct minstrel_sta_info *mi, int rix) >>>> { >>>> int i = rix; >>>> for (i = rix; i >= 0; i--) >>>> if (mi->r[i].rix == rix) >>>> 48: 3b 58 04 cmp 0x4(%eax),%ebx >>>> 4b: 74 4b je 98 <minstrel_tx_status+0x98> >>>> 4d: 83 c2 01 add $0x1,%edx >>>> >>>> It fails because of mi->r[i] being a NULL pointer. It is allocated in >>>> minstel_alloc_sta, but minstrel_ht_alloc_sta does not call that function. >>>> >>>> struct minstrel_ht_sta_priv holds a union with struct minstrel_ht_sta and >>>> struct minstrel_sta_info. During authenticate the bool is_ht is false so >>>> minstrel_ht_tx_status calls minstrel_tx_status, but minstrel_sta_info::r >>>> is not set until rate_init which is after assoc. >>> I'm not sure this is the right fix. If I understand the issue correctly, >>> mi->r is only NULL because .rate_init has not been called yet, which is >>> a bug that other rate control modules might trip over as well, maybe in >>> more subtle ways. If this is the case, then I believe this bug should be >>> fixed in mac80211 instead. >>> >>> Maybe it would even be a good idea to set a flag after calling >>> rate_control_rate_init, and calling WARN_ON or even BUG_ON when doing tx >>> before that. >>> >>> - Felix >>> >> >> Hi Felix, >> >> I am not sure I can agree. minstrel_ht allocates the struct >> minstrel_ht_sta_priv initializing is_ht to false thereby choosing a >> default and zero'ing the legacy field. When setting is_ht to false >> consequently the contents of the legacy field should be properly set as >> is done in minstrel_ht_update_caps (at use_legacy label). > Right, minstrel_ht_update_caps initializes that field, and it's always > called from .rate_init. > > While the non-HT minstrel initializes that field earlier (because it is > not stored anywhere else), it still also assumes that it isn't asked to > do tx until .rate_init is called. > > It doesn't matter whether it crashes in non-HT minstrel or not, the main > issue is that assumptions of both minstrel and minstrel_ht (and possibly > other rate control implementations) are being violated by mac80211. > > Before we can address that problem, we need to decide whether we want to > change the code to no longer require .rate_init before tx (which I think > is a bad idea, since there's no list of supported rates available yet at > that point in time), or if we change mac80211 to no longer violate those > assumptions. In either case, this patch is insufficient. > > My two cents: Felix is right---this whole process is a bit confusing and hard to work around. I know that iwlwifi has had to implement a bunch of weird things because of the strange order in which mac80211 tells rate modules about clients. Taking the time work out a sane order, that's clearly specified, would help a lot in this space. We can patch minstrel_ht but it doesn't make it easier for other modules. > > Dan > Ok, I think we are discussing the rate_control interface here and what ops is called when. The .alloc_sta is being called when a sta is created. The .rate_init callback is called at different points in mac80211 depending on the mode (STA, P2P, TDLS, etc.). Commonality seems to be that .rate_init is being called when the connection has been established, ie. when the actual rates to be used over that connection are known/negotiated. Before this point the supported rates available are basically the ones supported by the local device and these are known upon calling .alloc_sta. The negotiated rates are always the supported rates or a subset. Gr. AvS -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
