diff options
authorNeil Horman <nhorman@tuxdriver.com>2011-03-04 19:26:03 -0500
committerLinus Torvalds <torvalds@linux-foundation.org>2011-03-04 17:28:52 -0800
commite9e3d724e2145f5039b423c290ce2b2c3d8f94bc (patch)
parent3256f80fbbc25bd2504bd564844c615227621e56 (diff)
nfs4: Ensure that ACL pages sent over NFS were not allocated from the slab (v3)
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 myself 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 triggerable by an uprivlidged user, so I'm CCing security on this as well. Signed-off-by: Neil Horman <nhorman@tuxdriver.com> CC: Trond Myklebust <Trond.Myklebust@netapp.com> CC: security@kernel.org CC: Jeff Layton <jlayton@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 files changed, 42 insertions, 2 deletions
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 78936a8f40ab..1ff76acc7e98 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -51,6 +51,7 @@
#include <linux/sunrpc/bc_xprt.h>
#include <linux/xattr.h>
#include <linux/utsname.h>
+#include <linux/mm.h>
#include "nfs4_fs.h"
#include "delegation.h"
@@ -3252,6 +3253,35 @@ static void buf_to_pages(const void *buf, size_t buflen,
+static int buf_to_pages_noslab(const void *buf, size_t buflen,
+ struct page **pages, unsigned int *pgbase)
+ struct page *newpage, **spages;
+ int rc = 0;
+ size_t len;
+ spages = pages;
+ do {
+ len = min(PAGE_CACHE_SIZE, buflen);
+ newpage = alloc_page(GFP_KERNEL);
+ if (newpage == NULL)
+ goto unwind;
+ memcpy(page_address(newpage), buf, len);
+ buf += len;
+ buflen -= len;
+ *pages++ = newpage;
+ rc++;
+ } while (buflen != 0);
+ return rc;
+ for(; rc > 0; rc--)
+ __free_page(spages[rc-1]);
+ return -ENOMEM;
struct nfs4_cached_acl {
int cached;
size_t len;
@@ -3420,13 +3450,23 @@ static int __nfs4_proc_set_acl(struct inode *inode, const void *buf, size_t bufl
.rpc_argp = &arg,
.rpc_resp = &res,
- int ret;
+ int ret, i;
if (!nfs4_server_supports_acls(server))
+ i = buf_to_pages_noslab(buf, buflen, arg.acl_pages, &arg.acl_pgbase);
+ if (i < 0)
+ return i;
- buf_to_pages(buf, buflen, arg.acl_pages, &arg.acl_pgbase);
ret = nfs4_call_sync(server, &msg, &arg, &res, 1);
+ /*
+ * Free each page after tx, so the only ref left is
+ * held by the network stack
+ */
+ for (; i > 0; i--)
+ put_page(pages[i-1]);
* Acl update can result in inode attribute update.
* so mark the attribute cache invalid.