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Subject[PATCH AUTOSEL 4.4 14/15] ceph: fix buffer free while holding i_ceph_lock in __ceph_setxattr()
Date
From: Luis Henriques <lhenriques@suse.com>

[ Upstream commit 86968ef21596515958d5f0a40233d02be78ecec0 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/ceph/xattr.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/ceph/xattr.c b/fs/ceph/xattr.c
index b24275ef97f74..22e5f3432abbf 100644
--- a/fs/ceph/xattr.c
+++ b/fs/ceph/xattr.c
@@ -916,6 +916,7 @@ int __ceph_setxattr(struct dentry *dentry, const char *name,
struct ceph_inode_info *ci = ceph_inode(inode);
struct ceph_mds_client *mdsc = ceph_sb_to_client(dentry->d_sb)->mdsc;
struct ceph_cap_flush *prealloc_cf = NULL;
+ struct ceph_buffer *old_blob = NULL;
int issued;
int err;
int dirty = 0;
@@ -984,13 +985,15 @@ int __ceph_setxattr(struct dentry *dentry, const char *name,
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;
}
@@ -1006,6 +1009,7 @@ int __ceph_setxattr(struct dentry *dentry, const char *name,
}

spin_unlock(&ci->i_ceph_lock);
+ ceph_buffer_put(old_blob);
if (lock_snap_rwsem)
up_read(&mdsc->snap_rwsem);
if (dirty)
--
2.20.1
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