| Message ID | 1289341724.7380.13.camel@dan |
|---|---|
| State | Superseded, archived |
| Delegated to: | David Miller |
| Headers | show |
On Tue, 2010-11-09 at 17:28 -0500, Dan Rosenberg wrote: > The "mem" array used as scratch space for socket filters is not > initialized, allowing unprivileged users to leak kernel stack bytes. Hi Dan. Using type var[count] = {}; instead of type var[count]; ... memset(var, 0, sizeof(var)); at least for gcc 4.4 and 4.5 generally results in smaller code. $ size net/core/filter.o* text data bss dec hex filename 6751 56 1736 8543 215f net/core/filter.o.memset 6749 56 1736 8541 215d net/core/filter.o.init -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Dan Rosenberg <drosenberg@vsecurity.com> Date: Tue, 09 Nov 2010 17:28:44 -0500 > The "mem" array used as scratch space for socket filters is not > initialized, allowing unprivileged users to leak kernel stack bytes. > > Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com> Prove it. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Le mardi 09 novembre 2010 à 21:28 -0800, David Miller a écrit : > From: Dan Rosenberg <drosenberg@vsecurity.com> > Date: Tue, 09 Nov 2010 17:28:44 -0500 > > > The "mem" array used as scratch space for socket filters is not > > initialized, allowing unprivileged users to leak kernel stack bytes. > > > > Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com> > > Prove it. And once done, add the checks in sk_chk_filter() ? Allow a load of mem[X] only if a prior store of mem[X] is proven. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
> > Prove it. I hope this was a joke. In either case, my reply is a joke: http://lists.grok.org.uk/pipermail/full-disclosure/2010-November/077321.html -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
For reasons I don't understand, this code seems to cause some people's machines to lock up: BUG: soft lockup - CPU#0 stuck for 10s! [dz:11844] I haven't been able to reproduce this myself. Very strange. I'll send a stack trace if I can reproduce. -Dan On Wed, 2010-11-10 at 06:12 -0500, Dan Rosenberg wrote: > > > > Prove it. > > I hope this was a joke. In either case, my reply is a joke: > > http://lists.grok.org.uk/pipermail/full-disclosure/2010-November/077321.html -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Dan Rosenberg <drosenberg@vsecurity.com> Date: Wed, 10 Nov 2010 06:12:47 -0500 > >> >> Prove it. > > I hope this was a joke. It absolutely is not. You are very much not the first person ever to try and add an expensive memset() here. So the onus is really on you to prove this assertion and show the exact code path by which the user can actually see any uninitialized kernel stack memory (he can't, he can peek at certain values in a certain extremely contrived range, making the leak useless), rather than point us at some web external site archive of a list posting which we cannot easily quote and reply to here. I think you cannot do it, really. Except in the AF_PACKET case, the sockets can only see "0" or a negative error code, not the actual sk_run_filter() return value. In the one exception, AF_PACKET, the range of values the user can see are in the range of MTU of the device being accessed, which realistically is 1500 bytes. This means the user cannot see any kernel stack value outside of the range 0 to 1500, which isn't worth using this expensive memset to guard against at all. I don't even think it's worth adding all of the extra cpu cycles incurred by Eric Dumazet's scheme of using a bitmap test on every single memory buffer access. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/core/filter.c b/net/core/filter.c index 7beaec3..2749ba0 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -121,6 +121,8 @@ unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int int k; int pc; + memset(mem, 0, sizeof(mem)); + /* * Process array of filter instructions. */
The "mem" array used as scratch space for socket filters is not initialized, allowing unprivileged users to leak kernel stack bytes. Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com> --- net/core/filter.c | 2 ++ 1 file changed, 2 insertions(+), 0 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html