lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Tue, 26 Jul 2011 17:35:28 -0700 (PDT)
From:	Andi Kleen <andi@...stfloor.org>
To:	nhorman@...driver.com, ak@...ux.intel.com,
	Trond.Myklebust@...app.com, security@...nel.org,
	jlayton@...hat.com, torvalds@...ux-foundation.org, gregkh@...e.de,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	tim.bird@...sony.com, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: [PATCH] [36/98] nfs4: Ensure that ACL pages sent over NFS were not allocated from the slab (v3)

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Neil Horman <nhorman@...driver.com>

commit e9e3d724e2145f5039b423c290ce2b2c3d8f94bc upstream.

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@...driver.com>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>
CC: Trond Myklebust <Trond.Myklebust@...app.com>
CC: security@...nel.org
CC: Jeff Layton <jlayton@...hat.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
---
 fs/nfs/nfs4proc.c |   43 +++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 41 insertions(+), 2 deletions(-)

Index: linux-2.6.35.y/fs/nfs/nfs4proc.c
===================================================================
--- linux-2.6.35.y.orig/fs/nfs/nfs4proc.c
+++ linux-2.6.35.y/fs/nfs/nfs4proc.c
@@ -3275,6 +3275,35 @@ static void buf_to_pages(const void *buf
 	}
 }
 
+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;
@@ -3441,13 +3470,23 @@ static int __nfs4_proc_set_acl(struct in
 		.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]);
+
 	nfs_access_zap_cache(inode);
 	nfs_zap_acl_cache(inode);
 	return ret;
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists