On Fri, Oct 06, 2017 at 04:07:40PM -0400, Brian Foster wrote: > xfs_attr3_root_inactive() walks the attr fork tree to invalidate the > associated blocks. xfs_attr3_node_inactive() recursively descends > from internal blocks to leaf blocks, caching block address values > along the way to revisit parent blocks, locate the next entry and > descend down that branch of the tree. > > The code that attempts to reread the parent block is unsafe because > it assumes that the local xfs_da_node_entry pointer remains valid > after an xfs_trans_brelse() and re-read of the parent buffer. Under > heavy memory pressure, it is possible that the buffer has been > reclaimed and reallocated by the time the parent block is reread. > This means that 'btree' can point to an invalid memory address, lead > to a random/garbage value for child_fsb and cause the subsequent > read of the attr fork to go off the rails and return a NULL buffer > for an attr fork offset that is most likely not allocated. > > Note that this problem can be manufactured by setting > XFS_ATTR_BTREE_REF to 0 to prevent LRU caching of attr buffers, > creating a file with a multi-level attr fork and removing it to > trigger inactivation. > > To address this problem, reinit the node/btree pointers to the > parent buffer after it has been re-read. This ensures btree points > to a valid record and allows the walk to proceed. > > Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx> Looks ok, Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> /me wonders if this is a good enough reason to introduce a new errortag that turns xfs_buf_set_ref into a no-op and fills bp->b_addr with garbage prior to releasing the memory to weed out any other dangling pointers? > --- > > I suspect this is the cause of the NULL buf problem down in > xfs_attr_inactive(). I can manufacture an instance of that problem as > noted above. We have a customer who's hitting that problem and will > attempt to validate this fix, but there is no confirmation as of yet. > I'm posting this for review in the meantime because this seems like a > legit fix regardless of whether they are hitting this or something else. Let me know what they report back. --D > Brian > > fs/xfs/xfs_attr_inactive.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/fs/xfs/xfs_attr_inactive.c b/fs/xfs/xfs_attr_inactive.c > index ebd66b1..e3a950e 100644 > --- a/fs/xfs/xfs_attr_inactive.c > +++ b/fs/xfs/xfs_attr_inactive.c > @@ -302,6 +302,8 @@ xfs_attr3_node_inactive( > &bp, XFS_ATTR_FORK); > if (error) > return error; > + node = bp->b_addr; > + btree = dp->d_ops->node_tree_p(node); > child_fsb = be32_to_cpu(btree[i + 1].before); > xfs_trans_brelse(*trans, bp); > } > -- > 2.9.5 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
