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

Please note that each of these patches requires 5c498950f730 ("libceph:
allow ceph_buffer_put() to receive a NULL ceph_buffer").

Thanks,

Ilya

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