On Fri, May 11, 2018 at 11:20:57AM +1000, Dave Chinner wrote: > > From: Dave Chinner <dchinner@xxxxxxxxxx> > > We recently had an oops reported on a 4.14 kernel in > xfs_reclaim_inodes_count() where sb->s_fs_info pointed to garbage > and so the m_perag_tree lookup walked into lala land. It produces > an oops down this path during the failed mount: > > radix_tree_gang_lookup_tag+0xc4/0x130 > xfs_perag_get_tag+0x37/0xf0 > xfs_reclaim_inodes_count+0x32/0x40 > xfs_fs_nr_cached_objects+0x11/0x20 > super_cache_count+0x35/0xc0 > shrink_slab.part.66+0xb1/0x370 > shrink_node+0x7e/0x1a0 > try_to_free_pages+0x199/0x470 > __alloc_pages_slowpath+0x3a1/0xd20 > __alloc_pages_nodemask+0x1c3/0x200 > cache_grow_begin+0x20b/0x2e0 > fallback_alloc+0x160/0x200 > kmem_cache_alloc+0x111/0x4e0 > > The problem is that the superblock shrinker is running before the > filesystem structures it depends on have been fully set up. i.e. > the shrinker is registered in sget(), before ->fill_super() has been > called, and the shrinker can call into the filesystem before > fill_super() does it's setup work. Essentially we are exposed to > both use-after-free and use-before-initialisation bugs here. > > To fix this, add a check for the SB_BORN flag in super_cache_count. > In general, this flag is not set until ->fs_mount() completes > successfully, so we know that it is set after the filesystem > setup has completed. This matches the trylock_super() behaviour > which will not let super_cache_scan() run if SB_BORN is not set, and > hence will not allow the superblock shrinker from entering the > filesystem while it is being set up or after it has failed setup > and is being torn down. > > Signed-Off-By: Dave Chinner <dchinner@xxxxxxxxxx> Umm... Shouldn't that be Cc: stable, or is there something subtle I'm missing here?
