From e9e3d724e2145f5039b423c290ce2b2c3d8f94bc Mon Sep 17 00:00:00 2001 From: Neil Horman Date: Fri, 4 Mar 2011 19:26:03 -0500 Subject: [PATCH] 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 CC: Trond Myklebust CC: security@kernel.org CC: Jeff Layton Signed-off-by: Linus Torvalds --- fs/nfs/nfs4proc.c | 44 ++++++++++++++++++++++++++++++++++++++++++-- 1 file 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 #include #include +#include #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; + +unwind: + 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)) return -EOPNOTSUPP; + i = buf_to_pages_noslab(buf, buflen, arg.acl_pages, &arg.acl_pgbase); + if (i < 0) + return i; nfs_inode_return_delegation(inode); - 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. -- 2.20.1