Commit 86968ef2 authored Jul 19, 2019 by Luis Henriques Committed by Ilya Dryomov Aug 22, 2019

ceph: fix buffer free while holding i_ceph_lock in __ceph_setxattr()



Calling ceph_buffer_put() in __ceph_setxattr() may end up freeing the
i_xattrs.prealloc_blob buffer while holding the i_ceph_lock.  This can be
fixed by postponing the call until later, when the lock is released.

The following backtrace was triggered by fstests generic/117.

  BUG: sleeping function called from invalid context at mm/vmalloc.c:2283
  in_atomic(): 1, irqs_disabled(): 0, pid: 650, name: fsstress
  3 locks held by fsstress/650:
   #0: 00000000870a0fe8 (sb_writers#8){.+.+}, at: mnt_want_write+0x20/0x50
   #1: 00000000ba0c4c74 (&type->i_mutex_dir_key#6){++++}, at: vfs_setxattr+0x55/0xa0
   #2: 000000008dfbb3f2 (&(&ci->i_ceph_lock)->rlock){+.+.}, at: __ceph_setxattr+0x297/0x810
  CPU: 1 PID: 650 Comm: fsstress Not tainted 5.2.0+ #437
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58-prebuilt.qemu.org 04/01/2014
  Call Trace:
   dump_stack+0x67/0x90
   ___might_sleep.cold+0x9f/0xb1
   vfree+0x4b/0x60
   ceph_buffer_release+0x1b/0x60
   __ceph_setxattr+0x2b4/0x810
   __vfs_setxattr+0x66/0x80
   __vfs_setxattr_noperm+0x59/0xf0
   vfs_setxattr+0x81/0xa0
   setxattr+0x115/0x230
   ? filename_lookup+0xc9/0x140
   ? rcu_read_lock_sched_held+0x74/0x80
   ? rcu_sync_lockdep_assert+0x2e/0x60
   ? __sb_start_write+0x142/0x1a0
   ? mnt_want_write+0x20/0x50
   path_setxattr+0xba/0xd0
   __x64_sys_lsetxattr+0x24/0x30
   do_syscall_64+0x50/0x1c0
   entry_SYSCALL_64_after_hwframe+0x49/0xbe
  RIP: 0033:0x7ff23514359a

Signed-off-by: Luis Henriques <lhenriques@suse.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

parent 5c498950

fs/ceph/xattr.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -1036,6 +1036,7 @@ int __ceph_setxattr(struct inode inode, const char name,
		struct ceph_inode_info *ci = ceph_inode(inode);
		struct ceph_mds_client *mdsc = ceph_sb_to_client(inode->i_sb)->mdsc;
		struct ceph_cap_flush *prealloc_cf = NULL;
		struct ceph_buffer *old_blob = NULL;
		int issued;
		int err;
		int dirty = 0;
		@@ -1109,13 +1110,15 @@ retry:
		struct ceph_buffer *blob;

		spin_unlock(&ci->i_ceph_lock);
		dout(" preaallocating new blob size=%d\n", required_blob_size);
		ceph_buffer_put(old_blob); /* Shouldn't be required */
		dout(" pre-allocating new blob size=%d\n", required_blob_size);
		blob = ceph_buffer_new(required_blob_size, GFP_NOFS);
		if (!blob)
		goto do_sync_unlocked;
		spin_lock(&ci->i_ceph_lock);
		/* prealloc_blob can't be released while holding i_ceph_lock */
		if (ci->i_xattrs.prealloc_blob)
		ceph_buffer_put(ci->i_xattrs.prealloc_blob);
		old_blob = ci->i_xattrs.prealloc_blob;
		ci->i_xattrs.prealloc_blob = blob;
		goto retry;
		}
		@@ -1131,6 +1134,7 @@ retry:
		}

		spin_unlock(&ci->i_ceph_lock);
		ceph_buffer_put(old_blob);
		if (lock_snap_rwsem)
		up_read(&mdsc->snap_rwsem);
		if (dirty)

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