linux-ext4 - Re: REGRESSION: 37f4a24c2469: blk-mq: centralise related handling into blk_mq_get_driver

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20200925191902.543953-1-shakeelb@google.com>
Date:   Fri, 25 Sep 2020 12:19:02 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Roman Gushchin <guro@...com>, Ming Lei <ming.lei@...hat.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Theodore Y . Ts'o" <tytso@....edu>, Jens Axboe <axboe@...nel.dk>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Shakeel Butt <shakeelb@...gle.com>
Subject: Re: REGRESSION: 37f4a24c2469: blk-mq: centralise related handling
 into blk_mq_get_driver_tag

On Fri, Sep 25, 2020 at 10:58 AM Shakeel Butt <shakeelb@...gle.com>
wrote:
>
[snip]
>
> I don't think you can ignore the flushing. The __free_once() in
> ___cache_free() assumes there is a space available.
>
> BTW do_drain() also have the same issue.
>
> Why not move slabs_destroy() after we update ac->avail and memmove()?

Ming, can you please try the following patch?


From: Shakeel Butt <shakeelb@...gle.com>

[PATCH] mm: slab: fix potential infinite recursion in ___cache_free

With the commit 10befea91b61 ("mm: memcg/slab: use a single set of
kmem_caches for all allocations"), it becomes possible to call kfree()
from the slabs_destroy(). However if slabs_destroy() is being called for
the array_cache of the local CPU then this opens the potential scenario
of infinite recursion because kfree() called from slabs_destroy() can
call slabs_destroy() with the same array_cache of the local CPU. Since
the array_cache of the local CPU is not updated before calling
slabs_destroy(), it will try to free the same pages.

To fix the issue, simply update the cache before calling
slabs_destroy().

Signed-off-by: Shakeel Butt <shakeelb@...gle.com>
---
 mm/slab.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index 3160dff6fd76..f658e86ec8ce 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1632,6 +1632,10 @@ static void slab_destroy(struct kmem_cache *cachep, struct page *page)
 		kmem_cache_free(cachep->freelist_cache, freelist);
 }
 
+/*
+ * Update the size of the caches before calling slabs_destroy as it may
+ * recursively call kfree.
+ */
 static void slabs_destroy(struct kmem_cache *cachep, struct list_head *list)
 {
 	struct page *page, *n;
@@ -2153,8 +2157,8 @@ static void do_drain(void *arg)
 	spin_lock(&n->list_lock);
 	free_block(cachep, ac->entry, ac->avail, node, &list);
 	spin_unlock(&n->list_lock);
-	slabs_destroy(cachep, &list);
 	ac->avail = 0;
+	slabs_destroy(cachep, &list);
 }
 
 static void drain_cpu_caches(struct kmem_cache *cachep)
@@ -3402,9 +3406,9 @@ static void cache_flusharray(struct kmem_cache *cachep, struct array_cache *ac)
 	}
 #endif
 	spin_unlock(&n->list_lock);
-	slabs_destroy(cachep, &list);
 	ac->avail -= batchcount;
 	memmove(ac->entry, &(ac->entry[batchcount]), sizeof(void *)*ac->avail);
+	slabs_destroy(cachep, &list);
 }
 
 /*
-- 
2.28.0.681.g6f77f65b4e-goog