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From: Chengming Zhou In-Reply-To: <20240315095556.GC581298@cmpxchg.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 6F64A140006 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: ofucke17hk7ii5febykcoge1spokw59a X-HE-Tag: 1710499398-882575 X-HE-Meta: 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 JFxaOg0C PBqbgpRnv4kuCgO9Nw810+73AD4emlaw4i7heflTz5r72PnL5Zztug8ZDMtQuZ5Dny/toHW1YvFz+pIZUybZvSV5DwG4xqAAABEziSGQ7HxXyCekwSak/JQff77DwEyZILAnNG8N85AfSpXhqFcFSRPhtNAnZ7jneNgEo5miaeSPvODozPFgfuRv7JwcBoCCh2yG5x/r3jZftw/EXJiyVkMODWeJce/49fh9k1yxGP2Qm664= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2024/3/15 17:55, Johannes Weiner wrote: > When cachestat on shmem races with swapping and invalidation, there > are two possible bugs: > > 1) A swapin error can have resulted in a poisoned swap entry in the > shmem inode's xarray. Calling get_shadow_from_swap_cache() on it > will result in an out-of-bounds access to swapper_spaces[]. > > Validate the entry with non_swap_entry() before going further. > > 2) When we find a valid swap entry in the shmem's inode, the shadow > entry in the swapcache might not exist yet: swap IO is still in > progress and we're before __remove_mapping; swapin, invalidation, > or swapoff have removed the shadow from swapcache after we saw the > shmem swap entry. > > This will send a NULL to workingset_test_recent(). The latter > purely operates on pointer bits, so it won't crash - node 0, memcg > ID 0, eviction timestamp 0, etc. are all valid inputs - but it's a > bogus test. In theory that could result in a false "recently > evicted" count. > > Such a false positive wouldn't be the end of the world. But for > code clarity and (future) robustness, be explicit about this case. > > Bail on get_shadow_from_swap_cache() returning NULL. > > Fixes: cf264e1329fb ("cachestat: implement cachestat syscall") > Cc: stable@vger.kernel.org [v6.5+] > Reported-by: Chengming Zhou [Bug #1] > Reported-by: Jann Horn [Bug #2] > Signed-off-by: Johannes Weiner Looks good to me. Reviewed-by: Chengming Zhou Thanks. > --- > mm/filemap.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/mm/filemap.c b/mm/filemap.c > index 222adac7c9c5..0aa91bf6c1f7 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -4198,7 +4198,23 @@ static void filemap_cachestat(struct address_space *mapping, > /* shmem file - in swap cache */ > swp_entry_t swp = radix_to_swp_entry(folio); > > + /* swapin error results in poisoned entry */ > + if (non_swap_entry(swp)) > + goto resched; > + > + /* > + * Getting a swap entry from the shmem > + * inode means we beat > + * shmem_unuse(). rcu_read_lock() > + * ensures swapoff waits for us before > + * freeing the swapper space. However, > + * we can race with swapping and > + * invalidation, so there might not be > + * a shadow in the swapcache (yet). > + */ > shadow = get_shadow_from_swap_cache(swp); > + if (!shadow) > + goto resched; > } > #endif > if (workingset_test_recent(shadow, true, &workingset))