[PATCH openEuler-5.10-LTS 17/36] mm: fix null-ptr-deref in kswapd_is_running()

From: ZhangPeng zhangpeng362@huawei.com

maillist inclusion category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I6PKGM

Reference: https://lore.kernel.org/linux-mm/20220824071909.192535-1-wangkefeng.wang@hua...

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wapd_run/stop() will set pgdat->kswapd to NULL, which could race with kswapd_is_running() in kcompactd(),

kswapd_run/stop() kcompactd() kswapd_is_running() if (pgdat->kswapd) // load non-NULL pgdat->kswapd pgdat->kswapd = NULL task_is_running(pgdat->kswapd) // Null pointer derefence

The KASAN report the null-ptr-deref shown below,

vmscan: Failed to start kswapd on node 0 ... BUG: KASAN: null-ptr-deref in kcompactd+0x440/0x504 Read of size 8 at addr 0000000000000024 by task kcompactd0/37

CPU: 0 PID: 37 Comm: kcompactd0 Kdump: loaded Tainted: G OE 5.10.60 #1 Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015 Call trace: dump_backtrace+0x0/0x394 show_stack+0x34/0x4c dump_stack+0x158/0x1e4 __kasan_report+0x138/0x140 kasan_report+0x44/0xdc __asan_load8+0x94/0xd0 kcompactd+0x440/0x504 kthread+0x1a4/0x1f0 ret_from_fork+0x10/0x18

For race between kswapd_run() and kcompactd(), adding a temporary value when create a kthread, and only set it to pgdat->kswapd if kthread_run() return successful task_struct to fix the issue.

For race between kswapd_stop() and kcompactd(), let's call kcompactd_stop() before kswapd_stop() to fix the issue.

Signed-off-by: Kefeng Wang wangkefeng.wang@huawei.com

Conflicts: mm/vmscan.c

Signed-off-by: ZhangPeng zhangpeng362@huawei.com Reviewed-by: Kefeng Wang wangkefeng.wang@huawei.com Signed-off-by: Jialin Zhang zhangjialin11@huawei.com --- mm/memory_hotplug.c | 2 +- mm/vmscan.c | 10 ++++++---- 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 7456d825414d..d2dd2bfcaac3 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1483,8 +1483,8 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)

node_states_clear_node(node, &arg); if (arg.status_change_nid >= 0) { - kswapd_stop(node); kcompactd_stop(node); + kswapd_stop(node); }

writeback_set_ratelimit(); diff --git a/mm/vmscan.c b/mm/vmscan.c index 1b333a4d247a..ace42e822aab 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4329,17 +4329,19 @@ int kswapd_run(int nid) { pg_data_t *pgdat = NODE_DATA(nid); int ret = 0; + struct task_struct *t;

if (pgdat->kswapd) return 0;

- pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid); - if (IS_ERR(pgdat->kswapd)) { + t = kthread_run(kswapd, pgdat, "kswapd%d", nid); + if (IS_ERR(t)) { /* failure at boot is fatal */ BUG_ON(system_state < SYSTEM_RUNNING); pr_err("Failed to start kswapd on node %d\n", nid); - ret = PTR_ERR(pgdat->kswapd); - pgdat->kswapd = NULL; + ret = PTR_ERR(t); + } else { + pgdat->kswapd = t; } return ret; }