[PATCH 6.18 018/175] cgroup/dmem: fix NULL pointer dereference when setting max

Greg Kroah-Hartman
2026-02-09T14:27:56Z

From: Chen Ridong <chenridong@huawei.com>

commit 43151f812886be1855d2cba059f9c93e4729460b upstream.

An issue was triggered:

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 15 UID: 0 PID: 658 Comm: bash Tainted: 6.19.0-rc6-next-2026012
Tainted: [O]=OOT_MODULE
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
RIP: 0010:strcmp+0x10/0x30
RSP: 0018:ffffc900017f7dc0 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff888107cd4358
RDX: 0000000019f73907 RSI: ffffffff82cc381a RDI: 0000000000000000
RBP: ffff8881016bef0d R08: 000000006c0e7145 R09: 0000000056c0e714
R10: 0000000000000001 R11: ffff888107cd4358 R12: 0007ffffffffffff
R13: ffff888101399200 R14: ffff888100fcb360 R15: 0007ffffffffffff
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000105c79000 CR4: 00000000000006f0
Call Trace:
<TASK>
dmemcg_limit_write.constprop.0+0x16d/0x390
? __pfx_set_resource_max+0x10/0x10
kernfs_fop_write_iter+0x14e/0x200
vfs_write+0x367/0x510
ksys_write+0x66/0xe0
do_syscall_64+0x6b/0x390
entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7f42697e1887

It was trriggered setting max without limitation, the command is like:
"echo test/region0 > dmem.max". To fix this issue, add check whether
options is valid after parsing the region_name.

Fixes: b168ed458dde ("kernel/cgroup: Add "dmem" memory accounting cgroup")
Cc: stable@vger.kernel.org # v6.14+
Signed-off-by: Chen Ridong <chenridong@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/cgroup/dmem.c | 3 +++
1 file changed, 3 insertions(+)

--- a/kernel/cgroup/dmem.c
+++ b/kernel/cgroup/dmem.c
@@ -700,6 +700,9 @@ static ssize_t dmemcg_limit_write(struct
if (!region_name[0])
continue;

+ if (!options || !*options)
+ return -EINVAL;
+
rcu_read_lock();
region = dmemcg_get_region_by_name(region_name);
rcu_read_unlock();