[PATCH v2 1/2] xfs: fix tmpfile/selinux deadlock and initialize security/acl

[Brian Foster <bfoster@redhat.com>]

xfstests generic/004 reproduces an ilock deadlock using the tmpfile
interface when selinux is enabled. This occurs because
xfs_create_tmpfile() takes the ilock and then calls d_tmpfile(). The
latter eventually calls into xfs_xattr_get() which attempts to get the
lock again. E.g.:

xfs_io          D ffffffff81c134c0  4096  3561   3560 0x00000080
ffff8801176a1a68 0000000000000046 ffff8800b401b540 ffff8801176a1fd8
00000000001d5800 00000000001d5800 ffff8800b401b540 ffff8800b401b540
ffff8800b73a6bd0 fffffffeffffffff ffff8800b73a6bd8 ffff8800b5ddb480
Call Trace:
[<ffffffff8177f969>] schedule+0x29/0x70
[<ffffffff81783a65>] rwsem_down_read_failed+0xc5/0x120
[<ffffffffa05aa97f>] ? xfs_ilock_attr_map_shared+0x1f/0x50 [xfs]
[<ffffffff813b3434>] call_rwsem_down_read_failed+0x14/0x30
[<ffffffff810ed179>] ? down_read_nested+0x89/0xa0
[<ffffffffa05aa7f2>] ? xfs_ilock+0x122/0x250 [xfs]
[<ffffffffa05aa7f2>] xfs_ilock+0x122/0x250 [xfs]
[<ffffffffa05aa97f>] xfs_ilock_attr_map_shared+0x1f/0x50 [xfs]
[<ffffffffa05701d0>] xfs_attr_get+0x90/0xe0 [xfs]
[<ffffffffa0565e07>] xfs_xattr_get+0x37/0x50 [xfs]
[<ffffffff8124842f>] generic_getxattr+0x4f/0x70
[<ffffffff8133fd9e>] inode_doinit_with_dentry+0x1ae/0x650
[<ffffffff81340e0c>] selinux_d_instantiate+0x1c/0x20
[<ffffffff813351bb>] security_d_instantiate+0x1b/0x30
[<ffffffff81237db0>] d_instantiate+0x50/0x70
[<ffffffff81237e85>] d_tmpfile+0xb5/0xc0
[<ffffffffa05add02>] xfs_create_tmpfile+0x362/0x410 [xfs]
[<ffffffffa0559ac8>] xfs_vn_tmpfile+0x18/0x20 [xfs]
[<ffffffff81230388>] path_openat+0x228/0x6a0
[<ffffffff810230f9>] ? sched_clock+0x9/0x10
[<ffffffff8105a427>] ? kvm_clock_read+0x27/0x40
[<ffffffff8124054f>] ? __alloc_fd+0xaf/0x1f0
[<ffffffff8123101a>] do_filp_open+0x3a/0x90
[<ffffffff817845e7>] ? _raw_spin_unlock+0x27/0x40
[<ffffffff8124054f>] ? __alloc_fd+0xaf/0x1f0
[<ffffffff8121e3ce>] do_sys_open+0x12e/0x210
[<ffffffff8121e4ce>] SyS_open+0x1e/0x20
[<ffffffff8178eda9>] system_call_fastpath+0x16/0x1b

xfs_vn_tmpfile() also fails to initialize security or default acls on
the newly created inode.

The functionality missing from the tmpfile() handler is mostly covered
by xfs_vn_mknod() but it currently has no means to determine whether a
file is unnamed. Therefore, convert xfs_vn_mknod() to
xfs_generic_create() and add a parameter to trigger the tmpfile-specific
file creation and dentry mapping calls.

The d_tmpfile() call is removed from xfs_create_tmpfile() and pulled up
into the new handler to address the deadlock. E.g., xfs_create_tmpfile()
has committed the create transaction and unlocked the inode prior to
mapping the inode to the dentry.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/xfs/xfs_inode.c |  5 +++--
 fs/xfs/xfs_inode.h |  2 +-
 fs/xfs/xfs_iops.c  | 41 +++++++++++++++++++++++++++++------------
 3 files changed, 33 insertions(+), 15 deletions(-)

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 5e7a38f..768087b 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -1334,7 +1334,8 @@ int
 xfs_create_tmpfile(
 	struct xfs_inode	*dp,
 	struct dentry		*dentry,
-	umode_t			mode)
+	umode_t			mode,
+	struct xfs_inode	**ipp)
 {
 	struct xfs_mount	*mp = dp->i_mount;
 	struct xfs_inode	*ip = NULL;
@@ -1402,7 +1403,6 @@ xfs_create_tmpfile(
 	xfs_qm_vop_create_dqattach(tp, ip, udqp, gdqp, pdqp);
 
 	ip->i_d.di_nlink--;
-	d_tmpfile(dentry, VFS_I(ip));
 	error = xfs_iunlink(tp, ip);
 	if (error)
 		goto out_trans_abort;
@@ -1415,6 +1415,7 @@ xfs_create_tmpfile(
 	xfs_qm_dqrele(gdqp);
 	xfs_qm_dqrele(pdqp);
 
+	*ipp = ip;
 	return 0;
 
  out_trans_abort:
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 396cc1f..f2fcde5 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -334,7 +334,7 @@ int		xfs_lookup(struct xfs_inode *dp, struct xfs_name *name,
 int		xfs_create(struct xfs_inode *dp, struct xfs_name *name,
 			   umode_t mode, xfs_dev_t rdev, struct xfs_inode **ipp);
 int		xfs_create_tmpfile(struct xfs_inode *dp, struct dentry *dentry,
-			   umode_t mode);
+			   umode_t mode, struct xfs_inode **ipp);
 int		xfs_remove(struct xfs_inode *dp, struct xfs_name *name,
 			   struct xfs_inode *ip);
 int		xfs_link(struct xfs_inode *tdp, struct xfs_inode *sip,
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 89b07e4..301ecbf 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -124,15 +124,15 @@ xfs_cleanup_inode(
 	xfs_dentry_to_name(&teardown, dentry, 0);
 
 	xfs_remove(XFS_I(dir), &teardown, XFS_I(inode));
-	iput(inode);
 }
 
 STATIC int
-xfs_vn_mknod(
+xfs_generic_create(
 	struct inode	*dir,
 	struct dentry	*dentry,
 	umode_t		mode,
-	dev_t		rdev)
+	dev_t		rdev,
+	bool		tmpfile)	/* unnamed file */
 {
 	struct inode	*inode;
 	struct xfs_inode *ip = NULL;
@@ -156,8 +156,12 @@ xfs_vn_mknod(
 	if (error)
 		return error;
 
-	xfs_dentry_to_name(&name, dentry, mode);
-	error = xfs_create(XFS_I(dir), &name, mode, rdev, &ip);
+	if (!tmpfile) {
+		xfs_dentry_to_name(&name, dentry, mode);
+		error = xfs_create(XFS_I(dir), &name, mode, rdev, &ip);
+	} else {
+		error = xfs_create_tmpfile(XFS_I(dir), dentry, mode, &ip);
+	}
 	if (unlikely(error))
 		goto out_free_acl;
 
@@ -180,7 +184,11 @@ xfs_vn_mknod(
 	}
 #endif
 
-	d_instantiate(dentry, inode);
+	if (tmpfile)
+		d_tmpfile(dentry, inode);
+	else
+		d_instantiate(dentry, inode);
+
  out_free_acl:
 	if (default_acl)
 		posix_acl_release(default_acl);
@@ -189,11 +197,23 @@ xfs_vn_mknod(
 	return -error;
 
  out_cleanup_inode:
-	xfs_cleanup_inode(dir, inode, dentry);
+	if (!tmpfile)
+		xfs_cleanup_inode(dir, inode, dentry);
+	iput(inode);
 	goto out_free_acl;
 }
 
 STATIC int
+xfs_vn_mknod(
+	struct inode	*dir,
+	struct dentry	*dentry,
+	umode_t		mode,
+	dev_t		rdev)
+{
+	return xfs_generic_create(dir, dentry, mode, rdev, false);
+}
+
+STATIC int
 xfs_vn_create(
 	struct inode	*dir,
 	struct dentry	*dentry,
@@ -353,6 +373,7 @@ xfs_vn_symlink(
 
  out_cleanup_inode:
 	xfs_cleanup_inode(dir, inode, dentry);
+	iput(inode);
  out:
 	return -error;
 }
@@ -1053,11 +1074,7 @@ xfs_vn_tmpfile(
 	struct dentry	*dentry,
 	umode_t		mode)
 {
-	int		error;
-
-	error = xfs_create_tmpfile(XFS_I(dir), dentry, mode);
-
-	return -error;
+	return xfs_generic_create(dir, dentry, mode, 0, true);
 }
 
 static const struct inode_operations xfs_inode_operations = {
-- 
1.8.3.1

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