{"id":"CVE-2021-47566","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nproc/vmcore: fix clearing user buffer by properly using clear_user()\n\nTo clear a user buffer we cannot simply use memset, we have to use\nclear_user().  With a virtio-mem device that registers a vmcore_cb and\nhas some logically unplugged memory inside an added Linux memory block,\nI can easily trigger a BUG by copying the vmcore via \"cp\":\n\n  systemd[1]: Starting Kdump Vmcore Save Service...\n  kdump[420]: Kdump is using the default log level(3).\n  kdump[453]: saving to /sysroot/var/crash/127.0.0.1-2021-11-11-14:59:22/\n  kdump[458]: saving vmcore-dmesg.txt to /sysroot/var/crash/127.0.0.1-2021-11-11-14:59:22/\n  kdump[465]: saving vmcore-dmesg.txt complete\n  kdump[467]: saving vmcore\n  BUG: unable to handle page fault for address: 00007f2374e01000\n  #PF: supervisor write access in kernel mode\n  #PF: error_code(0x0003) - permissions violation\n  PGD 7a523067 P4D 7a523067 PUD 7a528067 PMD 7a525067 PTE 800000007048f867\n  Oops: 0003 [#1] PREEMPT SMP NOPTI\n  CPU: 0 PID: 468 Comm: cp Not tainted 5.15.0+ #6\n  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-27-g64f37cc530f1-prebuilt.qemu.org 04/01/2014\n  RIP: 0010:read_from_oldmem.part.0.cold+0x1d/0x86\n  Code: ff ff ff e8 05 ff fe ff e9 b9 e9 7f ff 48 89 de 48 c7 c7 38 3b 60 82 e8 f1 fe fe ff 83 fd 08 72 3c 49 8d 7d 08 4c 89 e9 89 e8 \u003c49\u003e c7 45 00 00 00 00 00 49 c7 44 05 f8 00 00 00 00 48 83 e7 f81\n  RSP: 0018:ffffc9000073be08 EFLAGS: 00010212\n  RAX: 0000000000001000 RBX: 00000000002fd000 RCX: 00007f2374e01000\n  RDX: 0000000000000001 RSI: 00000000ffffdfff RDI: 00007f2374e01008\n  RBP: 0000000000001000 R08: 0000000000000000 R09: ffffc9000073bc50\n  R10: ffffc9000073bc48 R11: ffffffff829461a8 R12: 000000000000f000\n  R13: 00007f2374e01000 R14: 0000000000000000 R15: ffff88807bd421e8\n  FS:  00007f2374e12140(0000) GS:ffff88807f000000(0000) knlGS:0000000000000000\n  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n  CR2: 00007f2374e01000 CR3: 000000007a4aa000 CR4: 0000000000350eb0\n  Call Trace:\n   read_vmcore+0x236/0x2c0\n   proc_reg_read+0x55/0xa0\n   vfs_read+0x95/0x190\n   ksys_read+0x4f/0xc0\n   do_syscall_64+0x3b/0x90\n   entry_SYSCALL_64_after_hwframe+0x44/0xae\n\nSome x86-64 CPUs have a CPU feature called \"Supervisor Mode Access\nPrevention (SMAP)\", which is used to detect wrong access from the kernel\nto user buffers like this: SMAP triggers a permissions violation on\nwrong access.  In the x86-64 variant of clear_user(), SMAP is properly\nhandled via clac()+stac().\n\nTo fix, properly use clear_user() when we're dealing with a user buffer.","modified":"2026-03-13T05:19:27.766216Z","published":"2024-05-24T15:15:21.637Z","related":["SUSE-SU-2024:2360-1","SUSE-SU-2024:2372-1","SUSE-SU-2024:2381-1","SUSE-SU-2024:2394-1","SUSE-SU-2024:2561-1","SUSE-SU-2024:2939-1"],"references":[{"type":"FIX","url":"https://git.kernel.org/stable/c/c1e63117711977cc4295b2ce73de29dd17066c82"},{"type":"FIX","url":"https://git.kernel.org/stable/c/fd7974c547abfb03072a4ee706d3a6f182266f89"},{"type":"FIX","url":"https://git.kernel.org/stable/c/33a7d698f30fa0b99d50569e9909d3baa65d8f6a"},{"type":"FIX","url":"https://git.kernel.org/stable/c/7b3a34f08d11e7f05cd00b8e09adaa15192f0ad1"},{"type":"FIX","url":"https://git.kernel.org/stable/c/99d348b82bcb36171f24411d3f1a15706a2a937a"},{"type":"FIX","url":"https://git.kernel.org/stable/c/9ef384ed300d1bcfb23d0ab0b487d544444d4b52"},{"type":"FIX","url":"https://git.kernel.org/stable/c/a8a917058faf4abaec9fb614bb6d5f8fe3529ec6"},{"type":"FIX","url":"https://git.kernel.org/stable/c/a9e164bd160be8cbee1df70acb379129e3cd2e7c"}],"affected":[{"database_specific":{"unresolved_ranges":[{"events":[{"introduced":"3.0"},{"fixed":"4.4.294"}]},{"events":[{"introduced":"4.5"},{"fixed":"4.9.292"}]},{"events":[{"introduced":"4.10"},{"fixed":"4.14.257"}]},{"events":[{"introduced":"4.15"},{"fixed":"4.19.219"}]},{"events":[{"introduced":"4.20"},{"fixed":"5.4.163"}]},{"events":[{"introduced":"5.5"},{"fixed":"5.10.83"}]},{"events":[{"introduced":"5.11"},{"fixed":"5.15.6"}]},{"events":[{"introduced":"0"},{"last_affected":"5.16-rc1"}]}],"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2021-47566.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}