Date: Mon, 7 Mar 2011 15:51:03 -0500 (EST) From: Josh Bressers <bressers@...hat.com> To: oss-security@...ts.openwall.com Cc: "Steven M. Christey" <coley@...us.mitre.org> Subject: Re: CVE request - kernel: nfs4: Ensure that ACL pages sent over NFS were not allocated from the slab Please use CVE-2011-1090 for this. Thanks. -- JB ----- Original Message ----- > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=e9e3d724e2145f5039b423c290ce2b2c3d8f94bc > > The "bad_page()" page allocator sanity check was reported recently > (call > chain as follows): > > bad_page+0x69/0x91 > free_hot_cold_page+0x81/0x144 > skb_release_data+0x5f/0x98 > __kfree_skb+0x11/0x1a > tcp_ack+0x6a3/0x1868 > tcp_rcv_established+0x7a6/0x8b9 > tcp_v4_do_rcv+0x2a/0x2fa > tcp_v4_rcv+0x9a2/0x9f6 > do_timer+0x2df/0x52c > ip_local_deliver+0x19d/0x263 > ip_rcv+0x539/0x57c > netif_receive_skb+0x470/0x49f > :virtio_net:virtnet_poll+0x46b/0x5c5 > net_rx_action+0xac/0x1b3 > __do_softirq+0x89/0x133 > call_softirq+0x1c/0x28 > do_softirq+0x2c/0x7d > do_IRQ+0xec/0xf5 > default_idle+0x0/0x50 > ret_from_intr+0x0/0xa > default_idle+0x29/0x50 > cpu_idle+0x95/0xb8 > start_kernel+0x220/0x225 > _sinittext+0x22f/0x236 > > It occurs because an skb with a fraglist was freed from the tcp > retransmit queue when it was acked, but a page on that fraglist had > PG_Slab set (indicating it was allocated from the Slab allocator > (which > means the free path above can't safely free it via put_page. > > We tracked this back to an nfsv4 setacl operation, in which the nfs > code > attempted to fill convert the passed in buffer to an array of pages in > __nfs4_proc_set_acl, which gets used by the skb->frags list in > xs_sendpages. __nfs4_proc_set_acl just converts each page in the > buffer > to a page struct via virt_to_page, but the vfs allocates the buffer > via > kmalloc, meaning the PG_slab bit is set. We can't create a buffer with > kmalloc and free it later in the tcp ack path with put_page, so we > need > to either: > > 1) ensure that when we create the list of pages, no page struct has > PG_Slab set > > or > > 2) not use a page list to send this data > > Given that these buffers can be multiple pages and arbitrarily sized, > I > think (1) is the right way to go. I've written the below patch to > allocate a page from the buddy allocator directly and copy the data > over > to it. This ensures that we have a put_page free-able page for every > entry that winds up on an skb frag list, so it can be safely freed > when > the frame is acked. We do a put page on each entry after the > rpc_call_sync call so as to drop our own reference count to the page, > leaving only the ref count taken by tcp_sendpages. This way the data > will be properly freed when the ack comes in > > Successfully tested by [Neil Horman] to solve the above oops. > > Note, as this is the result of a setacl operation that exceeded a page > of data, I think this amounts to a local DOS trigger-able by an > privileged user, so [Neil Horman] CCing security on this as well. > > Thanks, Eugene > -- > Eugene Teo / Red Hat Security Response Team
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