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Subject: Re: [PATCH] nfsd: fix race between cache_clean and cache_purge
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <5eed50660eb13326b0fbf537fb58481ea53c1acb.1585043174.git.wuyihao@linux.alibaba.com>
Date:   Tue, 24 Mar 2020 09:38:55 -0400
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        Yihao Wu <wuyihao@linux.alibaba.com>
Content-Transfer-Encoding: quoted-printable
Message-Id: <8B2BC124-6911-46C9-9B01-A237AC149F0A@oracle.com>
References: <5eed50660eb13326b0fbf537fb58481ea53c1acb.1585043174.git.wuyihao@linux.alibaba.com>
To:     Bruce Fields <bfields@fieldses.org>,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        NeilBrown <neilb@suse.com>
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk


> On Mar 24, 2020, at 5:49 AM, Yihao Wu <wuyihao@linux.alibaba.com> =
wrote:
>=20
> cache_purge should hold cache_list_lock as cache_clean does. Otherwise =
a cache
> can be cache_put twice, which leads to a use-after-free bug.
>=20
> To reproduce, run ltp. It happens rarely.  /opt/ltp/runltp run -f =
net.nfs
>=20
> [14454.137661] =
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> [14454.138863] BUG: KASAN: use-after-free in cache_purge+0xce/0x160 =
[sunrpc]
> [14454.139822] Read of size 4 at addr ffff8883d484d560 by task =
nfsd/31993
> [14454.140746]
> [14454.140995] CPU: 1 PID: 31993 Comm: nfsd Kdump: loaded Not tainted =
4.19.91-0.229.git.87bac30.al7.x86_64.debug #1
> [14454.141002] Call Trace:
> [14454.141014]  dump_stack+0xaf/0xfb[14454.141027]  =
print_address_description+0x6a/0x2a0
> [14454.141037]  kasan_report+0x166/0x2b0[14454.141057]  ? =
cache_purge+0xce/0x160 [sunrpc]
> [14454.141079]  cache_purge+0xce/0x160 [sunrpc]
> [14454.141099]  nfsd_last_thread+0x267/0x270 [nfsd][14454.141109]  ? =
nfsd_last_thread+0x5/0x270 [nfsd]
> [14454.141130]  nfsd_destroy+0xcb/0x180 [nfsd]
> [14454.141140]  ? nfsd_destroy+0x5/0x180 [nfsd]
> [14454.141153]  nfsd+0x1e4/0x2b0 [nfsd]
> [14454.141163]  ? nfsd+0x5/0x2b0 [nfsd]
> [14454.141173]  kthread+0x114/0x150
> [14454.141183]  ? nfsd_destroy+0x180/0x180 [nfsd]
> [14454.141187]  ? kthread_park+0xb0/0xb0
> [14454.141197]  ret_from_fork+0x3a/0x50
> [14454.141224]
> [14454.141475] Allocated by task 20918:
> [14454.142011]  kmem_cache_alloc_trace+0x9f/0x2e0
> [14454.142027]  sunrpc_cache_lookup+0xca/0x2f0 [sunrpc]
> [14454.142037]  svc_export_parse+0x1e7/0x930 [nfsd]
> [14454.142051]  cache_do_downcall+0x5a/0x80 [sunrpc]
> [14454.142064]  cache_downcall+0x78/0x180 [sunrpc]
> [14454.142078]  cache_write_procfs+0x57/0x80 [sunrpc]
> [14454.142083]  proc_reg_write+0x90/0xd0
> [14454.142088]  vfs_write+0xc2/0x1c0
> [14454.142092]  ksys_write+0x4d/0xd0
> [14454.142098]  do_syscall_64+0x60/0x250
> [14454.142103]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [14454.142106]
> [14454.142344] Freed by task 19165:
> [14454.142804]  kfree+0x114/0x300
> [14454.142819]  cache_clean+0x2a4/0x2e0 [sunrpc]
> [14454.142833]  cache_flush+0x24/0x60 [sunrpc]
> [14454.142845]  write_flush.isra.19+0xbe/0x100 [sunrpc]
> [14454.142849]  proc_reg_write+0x90/0xd0
> [14454.142853]  vfs_write+0xc2/0x1c0
> [14454.142856]  ksys_write+0x4d/0xd0
> [14454.142860]  do_syscall_64+0x60/0x250
> [14454.142865]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [14454.142867]
> [14454.143095] The buggy address belongs to the object at =
ffff8883d484d540 which belongs to the cache kmalloc-256 of size 256
> [14454.144842] The buggy address is located 32 bytes inside of  =
256-byte region [ffff8883d484d540, ffff8883d484d640)
> [14454.146463] The buggy address belongs to the page:
> [14454.147155] page:ffffea000f521300 count:1 mapcount:0 =
mapping:ffff888107c02e00 index:0xffff8883d484da40 compound_map count: 0
> [14454.148712] flags: 0x17fffc00010200(slab|head)
> [14454.149356] raw: 0017fffc00010200 ffffea000f4baf00 0000000200000002 =
ffff888107c02e00
> [14454.150453] raw: ffff8883d484da40 0000000080190001 00000001ffffffff =
0000000000000000
> [14454.151557] page dumped because: kasan: bad access detected
> [14454.152364]
> [14454.152606] Memory state around the buggy address:
> [14454.153300]  ffff8883d484d400: fb fb fb fb fb fb fb fb fb fb fb fb =
fb fb fb fb
> [14454.154319]  ffff8883d484d480: fb fb fb fb fb fb fb fb fb fb fb fb =
fb fb fb fb
> [14454.155324] >ffff8883d484d500: fc fc fc fc fc fc fc fc fb fb fb fb =
fb fb fb fb
> [14454.156334]                                                        =
^
> [14454.157237]  ffff8883d484d580: fb fb fb fb fb fb fb fb fb fb fb fb =
fb fb fb fb
> [14454.158262]  ffff8883d484d600: fb fb fb fb fb fb fb fb fc fc fc fc =
fc fc fc fc
> [14454.159282] =
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> [14454.160224] Disabling lock debugging due to kernel taint
>=20
> Fixes: 471a930ad7d1(SUNRPC: Drop all entries from cache_detail when =
cache_purge())
> Cc: stable@vger.kernel.org #v4.11+
> Signed-off-by: Yihao Wu <wuyihao@linux.alibaba.com>

Mechanically this looks OK, but I would feel more comfortable
if a domain expert could review this. Neil, Trond, Bruce?


> ---
> net/sunrpc/cache.c | 3 +++
> 1 file changed, 3 insertions(+)
>=20
> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
> index bd843a81afa0..3e523eefc47f 100644
> --- a/net/sunrpc/cache.c
> +++ b/net/sunrpc/cache.c
> @@ -524,9 +524,11 @@ void cache_purge(struct cache_detail *detail)
> 	struct hlist_node *tmp =3D NULL;
> 	int i =3D 0;
>=20
> +	spin_lock(&cache_list_lock);
> 	spin_lock(&detail->hash_lock);
> 	if (!detail->entries) {
> 		spin_unlock(&detail->hash_lock);
> +		spin_unlock(&cache_list_lock);
> 		return;
> 	}
>=20
> @@ -541,6 +543,7 @@ void cache_purge(struct cache_detail *detail)
> 		}
> 	}
> 	spin_unlock(&detail->hash_lock);
> +	spin_unlock(&cache_list_lock);
> }
> EXPORT_SYMBOL_GPL(cache_purge);
>=20
> --=20
> 2.20.1.2432.ga663e714
>=20

--
Chuck Lever