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mm/swap_state: update zswap LRU's protection range with the folio locked 

When a folio is swapped in, the protection size of the corresponding zswap
LRU is incremented, so that the zswap shrinker is more conservative with
its reclaiming action.  This field is embedded within the struct lruvec,
so updating it requires looking up the folio's memcg and lruvec.  However,
currently this lookup can happen after the folio is unlocked, for instance
if a new folio is allocated, and swap_read_folio() unlocks the folio
before returning.  In this scenario, there is no stability guarantee for
the binding between a folio and its memcg and lruvec:

* A folio's memcg and lruvec can be freed between the lookup and the
  update, leading to a UAF.
* Folio migration can clear the now-unlocked folio's memcg_data, which
  directs the zswap LRU protection size update towards the root memcg
  instead of the original memcg. This was recently picked up by the
  syzbot thanks to a warning in the inlined folio_lruvec() call.

Move the zswap LRU protection range update above the swap_read_folio()
call, and only when a new page is allocated, to prevent this.

[nphamcs@gmail.com: add VM_WARN_ON_ONCE() to zswap_folio_swapin()]
  Link: https://lkml.kernel.org/r/20240206180855.3987204-1-nphamcs@gmail.com
[nphamcs@gmail.com: remove unneeded if (folio) checks]
  Link: https://lkml.kernel.org/r/20240206191355.83755-1-nphamcs@gmail.com
Link: https://lkml.kernel.org/r/20240205232442.3240571-1-nphamcs@gmail.com
Fixes: b5ba474f3f ("zswap: shrink zswap pool based on memory pressure")
Reported-by: syzbot+17a611d10af7d18a7092@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000ae47f90610803260@google.com/
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Reviewed-by: Chengming Zhou <zhouchengming@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Nhat Pham 2024-02-05 15:24:42 -08:00 committed by Andrew Morton
parent 7efa6f2c80
commit 16e96ba5e9
2 changed files with 9 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
mm/swap_state.c
View File

@ -680,9 +680,10 @@ skip:
/* The page was likely read above, so no need for plugging here */
folio = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
&page_allocated, false);
if (unlikely(page_allocated))
if (unlikely(page_allocated)) {
zswap_folio_swapin(folio);
swap_read_folio(folio, false, NULL);
zswap_folio_swapin(folio);
}
return folio;
}
@ -855,9 +856,10 @@ skip:
/* The folio was likely read above, so no need for plugging here */
folio = __read_swap_cache_async(targ_entry, gfp_mask, mpol, targ_ilx,
&page_allocated, false);
if (unlikely(page_allocated))
if (unlikely(page_allocated)) {
zswap_folio_swapin(folio);
swap_read_folio(folio, false, NULL);
zswap_folio_swapin(folio);
}
return folio;
}

7
mm/zswap.c
View File

@ -377,10 +377,9 @@ void zswap_folio_swapin(struct folio *folio)
{
struct lruvec *lruvec;
if (folio) {
lruvec = folio_lruvec(folio);
atomic_long_inc(&lruvec->zswap_lruvec_state.nr_zswap_protected);
}
VM_WARN_ON_ONCE(!folio_test_locked(folio));
lruvec = folio_lruvec(folio);
atomic_long_inc(&lruvec->zswap_lruvec_state.nr_zswap_protected);
}
/*********************************