[lkml]   [2014]   [Jul]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: f2fs: Possible use-after-free when umount filesystem
Hi Gu,

>> Investigation shows, that f2fs_evict_inode, when called for 'meta_inode', uses invalidate_mapping_pages() for 'node_inode'.
>> But 'node_inode' is deleted before 'meta_inode' in f2fs_put_super via iput().
>> It seems that in common usage scenario this use-after-free is benign, because 'node_inode' remains partially valid data even after kmem_cache_free().
>> But things may change if, while 'meta_inode' is evicted in one f2fs filesystem, another (mounted) f2fs filesystem requests inode from cache, and formely
>> 'node_inode' of the first filesystem is returned.
> The analysis seems reasonable. Have you tried to swap the reclaim order of node_inde
> and meta_inode?
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 870fe19..e114418 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -430,8 +430,8 @@ static void f2fs_put_super(struct super_block *sb)
> if (sbi->s_dirty && get_pages(sbi, F2FS_DIRTY_NODES))
> write_checkpoint(sbi, true);
> - iput(sbi->node_inode);
> iput(sbi->meta_inode);
> + iput(sbi->node_inode);
> /* destroy f2fs internal modules */
> destroy_node_manager(sbi);
> Thanks,
> Gu

With reclaim order of node_inode and meta_inode swapped, use-after-free
error disappears.

But shouldn't initialization order of these inodes be swapped too?
As meta_inode uses node_inode, it seems logical that it should be
initialized after it.

Best regards,

Andrey Tsyvarev
Linux Verification Center, ISPRAS

 \ /
  Last update: 2014-07-22 12:41    [W:0.085 / U:2.332 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site