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[PATCH 4.9 48/51] xfs: remove racy hasattr check from attr ops

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4.9-stable review patch.  If anyone has any objections, please let me know.

------------------


From: Brian Foster <bfoster@redhat.com>

commit 5a93790d4e2df73e30c965ec6e49be82fc3ccfce upstream.

xfs_attr_[get|remove]() have unlocked attribute fork checks to optimize
away a lock cycle in cases where the fork does not exist or is otherwise
empty. This check is not safe, however, because an attribute fork short
form to extent format conversion includes a transient state that causes
the xfs_inode_hasattr() check to fail. Specifically,
xfs_attr_shortform_to_leaf() creates an empty extent format attribute
fork and then adds the existing shortform attributes to it.

This means that lookup of an existing xattr can spuriously return
-ENOATTR when racing against a setxattr that causes the associated
format conversion. This was originally reproduced by an untar on a
particularly configured glusterfs volume, but can also be reproduced on
demand with properly crafted xattr requests.

The format conversion occurs under the exclusive ilock. xfs_attr_get()
and xfs_attr_remove() already have the proper locking and checks further
down in the functions to handle this situation correctly. Drop the
unlocked checks to avoid the spurious failure and rely on the existing
logic.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/xfs/libxfs/xfs_attr.c |    6 ------
 1 file changed, 6 deletions(-)

--- a/fs/xfs/libxfs/xfs_attr.c
+++ b/fs/xfs/libxfs/xfs_attr.c
@@ -131,9 +131,6 @@ xfs_attr_get(
 	if (XFS_FORCED_SHUTDOWN(ip->i_mount))
 		return -EIO;
 
-	if (!xfs_inode_hasattr(ip))
-		return -ENOATTR;
-
 	error = xfs_attr_args_init(&args, ip, name, flags);
 	if (error)
 		return error;
@@ -392,9 +389,6 @@ xfs_attr_remove(
 	if (XFS_FORCED_SHUTDOWN(dp->i_mount))
 		return -EIO;
 
-	if (!xfs_inode_hasattr(dp))
-		return -ENOATTR;
-
 	error = xfs_attr_args_init(&args, dp, name, flags);
 	if (error)
 		return error;

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[PATCH 4.9 00/51] 4.9.8-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:40 +0100
  [PATCH 4.9 35/51] xfs: adjust allocation length in xfs_alloc_space_available Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:40 +0100
  [PATCH 4.9 36/51] xfs: dont rely on ->total in xfs_alloc_space_available Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:40 +0100
  [PATCH 4.9 09/51] tcp: fix tcp_fastopen unaligned access complaints on sparc Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:40 +0100
  [PATCH 4.9 05/51] mlxsw: pci: Fix EQE structure definition Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:40 +0100
  [PATCH 4.9 04/51] mlxsw: switchx2: Fix memory leak at skb reallocation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:40 +0100
  [PATCH 4.9 03/51] mlxsw: spectrum: Fix memory leak at skb reallocation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:40 +0100
  [PATCH 4.9 26/51] net: mpls: Fix multipath selection for LSR use case Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:40 +0100
  [PATCH 4.9 11/51] mlx4: do not call napi_schedule() without care Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 14/51] ax25: Fix segfault after sock connection timeout Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 47/51] xfs: verify dirblocklog correctly Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 43/51] xfs: sanity check inode di_mode Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 39/51] xfs: sanity check directory inode di_size Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 15/51] net sched actions: fix refcnt when GETing of action after bind Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 50/51] xfs: clear _XBF_PAGES from buffers when readahead page Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 22/51] ipv6: addrconf: Avoid addrconf_disable_change() using RCU read-side lock Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 31/51] lwtunnel: Fix oops on state free after encap module unload Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 23/51] tcp: initialize max window for a new fastopen socket Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 49/51] xfs: extsize hints are not unlikely in xfs_bmap_btalloc Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 24/51] net/mlx5e: Do not recycle pages from emergency reserve Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 08/51] net: systemport: Decouple flow control from __bcm_sysport_tx_reclaim Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 30/51] net: Specify the owning module for lwtunnel ops Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 20/51] net: phy: bcm63xx: Utilize correct config_intr function Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 27/51] r8152: dont execute runtime suspend if the tx is not empty Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 46/51] xfs: fix COW writeback race Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 44/51] xfs: dont wrap ID in xfs_dq_get_next_id Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 06/51] net: lwtunnel: Handle lwtunnel_fill_encap failure Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 42/51] xfs: sanity check inode mode when creating new dentry Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 32/51] net: dsa: Bring back device detaching in dsa_slave_suspend() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 41/51] xfs: replace xfs_mode_to_ftype table with switch statement Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 10/51] openvswitch: maintain correct checksum state in conntrack actions Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 13/51] ip6_tunnel: Account for tunnel header in tunnel MTU Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 45/51] xfs: fix xfs_mode_to_ftype() prototype Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 28/51] af_unix: move unix_mknod() out of bindlock Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 25/51] bridge: netlink: call br_changelink() during br_dev_newlink() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 34/51] xfs: fix bogus minleft manipulations Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 37/51] xfs: dont print warnings when xfs_log_force fails Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 48/51] xfs: remove racy hasattr check from attr ops Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 12/51] ravb: do not use zero-length alignment DMA descriptor Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 51/51] xfs: fix bmv_count confusion w/ shared extents Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 33/51] xfs: bump up reserved blocks in xfs_alloc_set_aside Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 19:50 +0100
  [PATCH 4.9 02/51] netvsc: add rcu_read locking to netvsc callback Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 20:00 +0100
  [PATCH 4.9 17/51] virtio-net: restore VIRTIO_HDR_F_DATA_VALID on receiving Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 20:00 +0100
  [PATCH 4.9 07/51] net: ipv4: fix table id in getroute response Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 20:00 +0100
  [PATCH 4.9 01/51] r8152: fix the sw rx checksum is unavailable Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 20:00 +0100
  Re: [PATCH 4.9 00/51] 4.9.8-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-02-02 21:40 +0100
    Re: [PATCH 4.9 00/51] 4.9.8-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-02 22:00 +0100
  Re: [PATCH 4.9 00/51] 4.9.8-stable review Guenter Roeck <linux@roeck-us.net> - 2017-02-03 06:20 +0100
    Re: [PATCH 4.9 00/51] 4.9.8-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-03 08:20 +0100

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