Re: [PATCH AUTOSEL 5.2 66/76] ceph: fix buffer free while holding i_ceph_lock in __ceph_setxattr()

Sasha Levin
2019-08-29T21:16:44Z

On Thu, Aug 29, 2019 at 10:51:04PM +0200, Ilya Dryomov wrote:
>On Thu, Aug 29, 2019 at 8:15 PM Sasha Levin <sashal@kernel.org> wrote:
>>
>> 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 0619adbcbe14c..8382299fc2d84 100644
>> --- a/fs/ceph/xattr.c
>> +++ b/fs/ceph/xattr.c
>> @@ -1028,6 +1028,7 @@ 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;
>> @@ -1101,13 +1102,15 @@ int __ceph_setxattr(struct inode *inode, 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;
>> }
>> @@ -1123,6 +1126,7 @@ int __ceph_setxattr(struct inode *inode, 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)
>
>Hi Sasha,
>
>I didn't tag i_ceph_lock series for stable because this is a very old
>bug which no one ever hit in real life, at least to my knowledge.

I can drop it if you prefer.

--
Thanks,
Sasha