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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: DS7PR12MB5910.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: a3524071-40e6-488e-a454-08ddb500a74b X-MS-Exchange-CrossTenant-originalarrivaltime: 26 Jun 2025 22:27:36.7546 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: WXKtYwP5RUeOK73+qNJqb7Q0D8aKftE9JGfzlDE/9tHVnuBV9AlgP8y7KAfounIK/YCDfRDzCcy464F9oL7SmA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR12MB8600 X-Rspamd-Queue-Id: E26BAC000B X-Rspam-User: X-Rspamd-Server: rspam06 X-Stat-Signature: 5d764c3g7xu7ste41gkxkdeh7arp8jgp X-HE-Tag: 1750976862-928429 X-HE-Meta: U2FsdGVkX1/s4+89r4EMGBx9yulBMz9FMddJENK8VP3ZODaU/ErAi9w49i44zy4VMYKDPLluHlu6BLCp3t8J5ifNfqStWIK6y/CvDE03qRSBO7sNfe6vgn8kLdU+xm0dcsD6S3ElZTFv/XsnLFr98H7MqMlif+mx/g7Dd+vYeDnj7EW/bTTqRoMOlYAMgj2XRJMl+VepzTuR5227cj4m9rS3sCGWHD0qCN3rXnp5tgeoxKnk0BUuZIpH2d958kH6ai6YuHMsa8GpImpHvPgX52jG7zhR2D1yzBOeeGjCtjmtWetOqPcRtDPGtJ8FG5Z2CoMMyJFENg2qslfArN432GqJSp035+uuSEdkewdYHJ6yj+7MYUSGYfU9eAmZbu/Plhq1k7J6BFB4nTY23Yz1TsHMSYFqWGRtWDJTyFAL7xF4xX5CiUYmWy8hJxwdG2ESTUXRxt+XGJctgJENiDdyDojTxxcip3sU9J+6FX09qUcS4eT8D3547ROpdUHJnCzmUbwk6bMnGCmgvqfDtWcT2zCBkCUfqVY8AuUWMzJsB5OHrt1snJoYI8HWD3dg7ohhtEiaPDaCcX9fNokFlrdZrGXgqT9ylxOaPEwE8mHa6pytOfd9HJ+VpK/b2VYqlSEw7XzokXA+BqS8QYEl9bn00T02AqJ8dAeTMSWtZD5ZbgOQYGP8tbcvZ3gH+j3oZbteC4knt5sMYz1nO+sdcQJVCkxhcznTu7gEDWI1AzLynafDZdH4XgKg+xL1Xv/RhHJjSS0k7u48KV5PBTAnz9QExGsSO0BJHJ4qzNX5T5I4DtUOC2NSqcgD51mVjPNTJXgvgsVEz5ysHSQzLGciRjmCn9mDqnFv3L19I+3s6mfuKefhmoBh8TWQ+AoT7vJ7vA/n5ja1BQ2uJyPE/1Dn9BpibK0vGRzD/LxdDlA7vDFqdtQBI/g38N2IHtbxfawX5bIuNLj8NXXt5Fx6BB3uQ+l VKiB10Xc 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello linux-mm team,=0A= =0A= I have found an interesting behavior in the Linux kernel: an unprivileged u= ser=0A= with access to user namespaces can cause privileged processes to be killed = due=0A= to an OOM situation on a single NUMA node, even if the system has plenty of= =0A= memory available on other NUMA nodes.=0A= =0A= This might lead to a local denial of service in some situations, so please= =0A= review and let me know if the current behavior is expected.=0A= =0A= The steps are simple:=0A= 1. Use a Linux system with multiple NUMA nodes=0A= 2. Enable unprivileged user namespaces (often distro dependent)=0A= 3. As an unprivileged user, create a user namespace + mount namespace=0A= and mount a tmpfs bound to NUMA node 1=0A= 4. Attempt to fill the tmpfs with more data than it can possibly store=0A= 5. The OOM killer will kill a significant amount of system daemons=0A= (UID 0).=0A= =0A= The possible mitigations I currently know of are: create a swap space, disa= ble=0A= unprivileged user namespaces, or set sysctl vm.oom_kill_allocating_task=3D1= .=0A= =0A= To be 100% clear, this does not require elevated privileges, and we are onl= y=0A= using a fraction of the total system memory.=0A= =0A= Below is an example on a Ubuntu 25.04 VM under qemu where I hotplugged a ne= w=0A= NUMA node with 1GB of memory, I also place the current process under a 2GB= =0A= memory cgroup to show that it's not an effective mitigation.=0A= =0A= $ uname -a=0A= Linux ubuntu 6.14.0-22-generic #22-Ubuntu SMP PREEMPT_DYNAMIC Wed May 21 15= :01:51 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux=0A= =0A= $ id -u=0A= 1000=0A= =0A= # Enable unprivileged user namespaces (this is an Ubuntu feature)=0A= $ sudo sysctl kernel.apparmor_restrict_unprivileged_userns=3D0=0A= =0A= $ sudo sh -c 'echo 2G > /sys/fs/cgroup/user.slice/user-1000.slice/memory.ma= x'=0A= =0A= $ numastat -mzc=0A= =0A= Per-node system memory usage (in MBs):=0A= Token Unaccepted not in hash table.=0A= Token Unaccepted not in hash table.=0A= Node 0 Node 1 Total=0A= ------ ------ -----=0A= MemTotal 7940 1024 8964=0A= MemFree 7533 1024 8557=0A= MemUsed 407 0 407=0A= Active 176 0 176=0A= Inactive 44 0 44=0A= Active(anon) 42 0 42=0A= Active(file) 134 0 134=0A= Inactive(file) 44 0 44=0A= Unevictable 26 0 26=0A= Mlocked 26 0 26=0A= Dirty 0 0 0=0A= FilePages 186 0 186=0A= Mapped 57 0 57=0A= AnonPages 59 0 59=0A= Shmem 1 0 1=0A= KernelStack 2 0 2=0A= PageTables 2 0 2=0A= Slab 84 0 84=0A= SReclaimable 17 0 17=0A= SUnreclaim 68 0 68=0A= KReclaimable 17 0 17=0A= =0A= $ unshare -U -r -m sh -xc 'mount -t tmpfs -o mpol=3Dbind:1 tmpfs /dev/shm ;= dd if=3D/dev/zero of=3D/dev/shm/file bs=3D64K count=3D25000'=0A= + mount -t tmpfs -o mpol=3Dbind:1 tmpfs /dev/shm=0A= + dd if=3D/dev/zero of=3D/dev/shm/file bs=3D64K count=3D25000=0A= [ 294.046130] Out of memory: Killed process 1074 (systemd) total-vm:21968k= B, anon-rss:2048kB, file-rss:10164kB, shmem-rss:0kB, UID:1000 pgtables:88kB= oom_score_adj:100=0A= [ 294.052224] Out of memory: Killed process 1076 ((sd-pam)) total-vm:21992= kB, anon-rss:1772kB, file-rss:1832kB, shmem-rss:0kB, UID:1000 pgtables:76kB= oom_score_adj:100=0A= [ 294.058446] Out of memory: Killed process 821 (unattended-upgr) total-vm= :121388kB, anon-rss:13272kB, file-rss:16004kB, shmem-rss:0kB, UID:0 pgtable= s:140kB oom_score_adj:0=0A= [ 294.064551] Out of memory: Killed process 423 (systemd-resolve) total-vm= :23200kB, anon-rss:2560kB, file-rss:11504kB, shmem-rss:0kB, UID:990 pgtable= s:88kB oom_score_adj:0=0A= [ 294.070491] Out of memory: Killed process 789 (udisksd) total-vm:470572k= B, anon-rss:1920kB, file-rss:11840kB, shmem-rss:0kB, UID:0 pgtables:136kB o= om_score_adj:0=0A= [ 294.076371] Out of memory: Killed process 848 (ModemManager) total-vm:39= 1392kB, anon-rss:1792kB, file-rss:10516kB, shmem-rss:0kB, UID:0 pgtables:12= 4kB oom_score_adj:0=0A= [ 294.082350] Out of memory: Killed process 733 (systemd-network) total-vm= :20804kB, anon-rss:1296kB, file-rss:10068kB, shmem-rss:0kB, UID:998 pgtable= s:76kB oom_score_adj:0=0A= [ 294.088273] Out of memory: Killed process 1141 ((resolved)) total-vm:206= 04kB, anon-rss:1280kB, file-rss:8556kB, shmem-rss:0kB, UID:0 pgtables:80kB = oom_score_adj:0=0A= [ 294.094350] Out of memory: Killed process 788 (systemd-logind) total-vm:= 18896kB, anon-rss:896kB, file-rss:7968kB, shmem-rss:0kB, UID:0 pgtables:84k= B oom_score_adj:0=0A= [ 294.100461] Out of memory: Killed process 1151 ((resolved)) total-vm:206= 04kB, anon-rss:1280kB, file-rss:7732kB, shmem-rss:0kB, UID:0 pgtables:84kB = oom_score_adj:0=0A= [ 294.106462] Out of memory: Killed process 1154 ((networkd)) total-vm:206= 04kB, anon-rss:1280kB, file-rss:8036kB, shmem-rss:0kB, UID:0 pgtables:84kB = oom_score_adj:0=0A= [ 294.112592] Out of memory: Killed process 1155 ((resolved)) total-vm:206= 04kB, anon-rss:1280kB, file-rss:8648kB, shmem-rss:0kB, UID:0 pgtables:84kB = oom_score_adj:0=0A= [ 294.118725] Out of memory: Killed process 1161 ((networkd)) total-vm:206= 04kB, anon-rss:1280kB, file-rss:8648kB, shmem-rss:0kB, UID:998 pgtables:84k= B oom_score_adj:0=0A= [ 294.124827] Out of memory: Killed process 1165 ((resolved)) total-vm:206= 04kB, anon-rss:1280kB, file-rss:8484kB, shmem-rss:0kB, UID:0 pgtables:88kB = oom_score_adj:0=0A= [ 294.131138] Out of memory: Killed process 1169 ((networkd)) total-vm:206= 04kB, anon-rss:1280kB, file-rss:8604kB, shmem-rss:0kB, UID:0 pgtables:80kB = oom_score_adj:0=0A= [ 294.137548] Out of memory: Killed process 1177 ((resolved)) total-vm:206= 04kB, anon-rss:1280kB, file-rss:8592kB, shmem-rss:0kB, UID:0 pgtables:84kB = oom_score_adj:0=0A= [ 294.144659] Out of memory: Killed process 1187 ((networkd)) total-vm:206= 04kB, anon-rss:1280kB, file-rss:8800kB, shmem-rss:0kB, UID:998 pgtables:80k= B oom_score_adj:0=0A= [ 294.151118] Out of memory: Killed process 1179 (systemd-logind) total-vm= :18728kB, anon-rss:1024kB, file-rss:7972kB, shmem-rss:0kB, UID:0 pgtables:7= 6kB oom_score_adj:0=0A= [ 294.157569] Out of memory: Killed process 1194 ((networkd)) total-vm:206= 04kB, anon-rss:1280kB, file-rss:8596kB, shmem-rss:0kB, UID:0 pgtables:80kB = oom_score_adj:0=0A= [ 294.163877] Out of memory: Killed process 417 (systemd-timesyn) total-vm= :91608kB, anon-rss:896kB, file-rss:7132kB, shmem-rss:0kB, UID:996 pgtables:= 88kB oom_score_adj:0=0A= [ 294.170240] Out of memory: Killed process 783 (polkitd) total-vm:306832k= B, anon-rss:640kB, file-rss:7264kB, shmem-rss:0kB, UID:988 pgtables:96kB oo= m_score_adj:0=0A= [ 294.176668] Out of memory: Killed process 1200 ((imesyncd)) total-vm:206= 04kB, anon-rss:1280kB, file-rss:7776kB, shmem-rss:0kB, UID:0 pgtables:84kB = oom_score_adj:0=0A= [ 294.183107] Out of memory: Killed process 1205 (9) total-vm:20136kB, ano= n-rss:1152kB, file-rss:6584kB, shmem-rss:0kB, UID:0 pgtables:80kB oom_score= _adj:0=0A= [ 294.189627] Out of memory: Killed process 1210 ((imesyncd)) total-vm:206= 04kB, anon-rss:1280kB, file-rss:7844kB, shmem-rss:0kB, UID:0 pgtables:80kB = oom_score_adj:0=0A= [ 294.196227] Out of memory: Killed process 1209 ((d-logind)) total-vm:201= 40kB, anon-rss:1280kB, file-rss:7284kB, shmem-rss:0kB, UID:0 pgtables:80kB = oom_score_adj:0=0A= [ 294.202956] Out of memory: Killed process 1212 ((imesyncd)) total-vm:206= 04kB, anon-rss:1280kB, file-rss:8568kB, shmem-rss:0kB, UID:0 pgtables:84kB = oom_score_adj:0=0A= [ 294.209719] Out of memory: Killed process 1223 ((imesyncd)) total-vm:206= 04kB, anon-rss:1280kB, file-rss:8556kB, shmem-rss:0kB, UID:0 pgtables:80kB = oom_score_adj:0=0A= [ 294.216356] Out of memory: Killed process 851 (rsyslogd) total-vm:220676= kB, anon-rss:1280kB, file-rss:4292kB, shmem-rss:0kB, UID:101 pgtables:80kB = oom_score_adj:0=0A= [ 294.223146] Out of memory: Killed process 1220 (systemd-logind) total-vm= :18728kB, anon-rss:1024kB, file-rss:8044kB, shmem-rss:0kB, UID:0 pgtables:8= 8kB oom_score_adj:0=0A= [ 294.229888] Out of memory: Killed process 1234 ((systemd)) total-vm:2199= 2kB, anon-rss:1664kB, file-rss:8852kB, shmem-rss:0kB, UID:0 pgtables:84kB o= om_score_adj:100=0A= [ 294.236624] Out of memory: Killed process 952 (login) total-vm:11220kB, = anon-rss:768kB, file-rss:4616kB, shmem-rss:0kB, UID:0 pgtables:64kB oom_sco= re_adj:0=0A= [ 294.243266] Out of memory: Killed process 940 (cron) total-vm:7512kB, an= on-rss:256kB, file-rss:2760kB, shmem-rss:0kB, UID:0 pgtables:56kB oom_score= _adj:0=0A= [ 294.249871] Out of memory: Killed process 956 (agetty) total-vm:8516kB, = anon-rss:128kB, file-rss:2492kB, shmem-rss:0kB, UID:0 pgtables:60kB oom_sco= re_adj:0=