Re: [PATCH] nfsd: fix race between cache_clean and cache_purge

Chuck Lever
2020-03-24T13:39:26Z

> On Mar 24, 2020, at 5:49 AM, Yihao Wu <wuyihao@linux.alibaba.com> wrote:
>
> 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.
>
> To reproduce, run ltp. It happens rarely. /opt/ltp/runltp run -f net.nfs
>
> [14454.137661] ==================================================================
> [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] ==================================================================
> [14454.160224] Disabling lock debugging due to kernel taint
>
> 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(+)
>
> 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 = NULL;
> int i = 0;
>
> + spin_lock(&cache_list_lock);
> spin_lock(&detail->hash_lock);
> if (!detail->entries) {
> spin_unlock(&detail->hash_lock);
> + spin_unlock(&cache_list_lock);
> return;
> }
>
> @@ -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);
>
> --
> 2.20.1.2432.ga663e714
>

--
Chuck Lever