On Tuesday, February 20, 2018 9:08:44 AM IST Chandan Rajendra wrote:
> generic/388 can cause the following "use after free" error to occur,
>
> =============================================================================
> BUG xfs_efi_item (Not tainted): Poison overwritten
> -----------------------------------------------------------------------------
>
> Disabling lock debugging due to kernel taint
> INFO: 0x00000000292c4bd4-0x00000000292c4bd4. First byte 0x6a instead of 0x6b
> INFO: Allocated in .kmem_zone_alloc+0xcc/0x190 age=79 cpu=0 pid=12436
> .__slab_alloc+0x54/0x80
> .kmem_cache_alloc+0x124/0x350
> .kmem_zone_alloc+0xcc/0x190
> .xfs_efi_init+0x48/0xf0
> .xfs_extent_free_create_intent+0x40/0x130
> .xfs_defer_intake_work+0x74/0x1e0
> .xfs_defer_finish+0xac/0x5c0
> .xfs_itruncate_extents+0x170/0x590
> .xfs_inactive_truncate+0xcc/0x170
> .xfs_inactive+0x1d8/0x2f0
> .xfs_fs_destroy_inode+0xe4/0x3d0
> .destroy_inode+0x68/0xb0
> .do_unlinkat+0x1e8/0x390
> system_call+0x58/0x6c
> INFO: Freed in .xfs_efi_item_free+0x44/0x80 age=79 cpu=0 pid=12436
> .kmem_cache_free+0x120/0x2b0
> .xfs_efi_item_free+0x44/0x80
> .xfs_trans_free_items+0xd4/0x130
> .__xfs_trans_commit+0xd0/0x350
> .xfs_trans_roll+0x4c/0x90
> .xfs_defer_trans_roll+0xa4/0x2b0
> .xfs_defer_finish+0xb8/0x5c0
> .xfs_itruncate_extents+0x170/0x590
> .xfs_inactive_truncate+0xcc/0x170
> .xfs_inactive+0x1d8/0x2f0
> .xfs_fs_destroy_inode+0xe4/0x3d0
> .destroy_inode+0x68/0xb0
> .do_unlinkat+0x1e8/0x390
> system_call+0x58/0x6c
>
> This happens due to the following interaction,
> 1. xfs_defer_finish() creates "extent free" intent item and adds it to the
> per-transction list of log items.
> 2. xfs_defer_trans_roll() invokes __xfs_trans_commit(). Here, if the
> XFS_MOUNT_FS_SHUTDOWN flag is set, we invoke io_unlock() operation
> for each of the log items in the per-transction list. For "extent
> free" log items xfs_efi_item_unlock() gets invoked which then frees
> the xfs_efi_log_item.
> 3. xfs_defer_trans_roll() then invokes xfs_defer_trans_abort(). Since the
> xfs_defer_pending->dfp_intent is still set to the "extent free" intent
> item, we invoke xfs_extent_free_abort_intent(). This accesses the
> previously freed xfs_efi_log_item to decrement the ref count.
>
> This commit fixes the bug by invoking xfs_defer_trans_abort() only when
> the log items in the per-transaction list have been committed to the
> CIL. The log item "committed" status is being tracked by
> xfs_defer_ops->dop_committed. This was the behaviour prior to commit
> 3ab78df2a59a485f479d26852a060acfd8c4ecd7 (xfs: rework xfs_bmap_free
> callers to use xfs_defer_ops).
>
> Reported-by: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Chandan Rajendra <chandan@xxxxxxxxxxxxxxxxxx>
> ---
> fs/xfs/libxfs/xfs_defer.c | 6 +++---
> fs/xfs/xfs_bmap_util.c | 2 +-
> fs/xfs/xfs_inode.c | 2 +-
> fs/xfs/xfs_trans.c | 8 +++++++-
> fs/xfs/xfs_trans.h | 2 +-
> fs/xfs/xfs_trans_inode.c | 2 +-
> 6 files changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
> index 087fea0..eb879a0 100644
> --- a/fs/xfs/libxfs/xfs_defer.c
> +++ b/fs/xfs/libxfs/xfs_defer.c
> @@ -256,13 +256,13 @@ xfs_defer_trans_roll(
> trace_xfs_defer_trans_roll((*tp)->t_mountp, dop);
>
> /* Roll the transaction. */
> - error = xfs_trans_roll(tp);
> + error = xfs_trans_roll(tp, &dop->dop_committed);
> if (error) {
> trace_xfs_defer_trans_roll_error((*tp)->t_mountp, dop, error);
> - xfs_defer_trans_abort(*tp, dop, error);
> + if (dop->dop_committed == true)
> + xfs_defer_trans_abort(*tp, dop, error);
> return error;
> }
> - dop->dop_committed = true;
>
> /* Rejoin the joined inodes. */
> for (i = 0; i < XFS_DEFER_OPS_NR_INODES && dop->dop_inodes[i]; i++)
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index c83f549..9d84d36 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -1830,7 +1830,7 @@ xfs_swap_change_owner(
> if (error != -EAGAIN)
> break;
>
> - error = xfs_trans_roll(tpp);
> + error = xfs_trans_roll(tpp, NULL);
> if (error)
> break;
> tp = *tpp;
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 604ee38..6419549 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -1049,7 +1049,7 @@ xfs_dir_ialloc(
> tp->t_flags &= ~(XFS_TRANS_DQ_DIRTY);
> }
>
> - code = xfs_trans_roll(&tp);
> + code = xfs_trans_roll(&tp, NULL);
> if (committed != NULL)
> *committed = 1;
I noticed that xfs_dir_ialloc() gets a "committed" argument passed to it.
I think I can pass this on to xfs_trans_roll() instead of the NULL pointer.
I will read up the code and decide on the next action.
--
chandan
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