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Re: Memory corruption due to word sharing

On Thu, 2 Feb 2012, David Sterba wrote:

> On Wed, Feb 01, 2012 at 04:19:18PM +0100, Jan Kara wrote:
> > We actually spotted this race in practice in btrfs on structure
> > fs/btrfs/ctree.h:struct btrfs_block_rsv where spinlock content got
> > corrupted due to update of following bitfield and there seem to be other
> > places in kernel where this could happen.
> Here's the list of structures where a bitfield is shared with spinlock
> or atomic/kref within an 8B word, generated from 3.3-rc2:
> spinlock+bitfield:
> Struct: struct ak4113; Field: init
> Struct: struct ak4114; Field: init
> Struct: struct ak4117; Field: init
> Struct: struct btrfs_block_rsv; Field: full
> Struct: struct cm109_dev; Field: buzzer_pending
> Struct: struct pch_udc_dev; Field: active
> Struct: struct rds_iw_device; Field: dma_local_lkey
> Struct: struct sierra_intf_private; Field: suspended
> Struct: struct sm501_gpio; Field: registered
> Struct: struct unix_sock; Field: gc_candidate
> Struct: struct usb_anchor; Field: poisoned
> Struct: struct usb_wwan_intf_private; Field: suspended
> atomic/kref+bitfield:
> Struct: struct dlm_lock_resource; Field: migration_pending
> Struct: struct extent_map; Field: in_tree
> Struct: struct kobject; Field: state_initialized
> Struct: struct page; Field: inuse
> Struct: struct rds_ib_connection; Field: i_flowctl
> Struct: struct rds_iw_connection; Field: i_flowctl
> Struct: struct sctp_transport; Field: dead
> Struct: struct transaction_s; Field: t_synchronous_commit
> Struct: struct xfs_ioend; Field: io_isasync
> Not all listed structs are necessarily subject to the bug. There may be
> another mechanism preventing concurrent access to the bitfield and
> spinlock/atomic, or the bitfield is modified from a single cpu, or is
> not used. But all of them need to be reviewed of course.

To hit this bug the containing objects also have to be at least
8-byte aligned.


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