CVE-2021-47566: proc/vmcore: fix clearing user buffer by properly using clear_user()
In the Linux kernel, the following vulnerability has been resolved:
proc/vmcore: fix clearing user buffer by properly using clearuser()
The Linux kernel CVE team has assigned CVE-2021-47566 to this issue.
Upstream advisory: https://lore.kernel.org/linux-cve-announce/2024052453-CVE-2021-47566-12b8@gregkh/T
Other sources
In the Linux kernel, the following vulnerability has been resolved:
proc/vmcore: fix clearing user buffer by properly using clearuser()
To clear a user buffer we cannot simply use memset, we have to use clearuser(). With a virtio-mem device that registers a vmcorecb and has some logically unplugged memory inside an added Linux memory block, I can easily trigger a BUG by copying the vmcore via "cp":
systemd[1]: Starting Kdump Vmcore Save Service... kdump[420]: Kdump is using the default log level(3). kdump[453]: saving to /sysroot/var/crash/127.0.0.1-2021-11-11-14:59:22/ kdump[458]: saving vmcore-dmesg.txt to /sysroot/var/crash/127.0.0.1-2021-11-11-14:59:22/ kdump[465]: saving vmcore-dmesg.txt complete kdump[467]: saving vmcore BUG: unable to handle page fault for address: 00007f2374e01000 #PF: supervisor write access in kernel mode #PF: errorcode(0x0003) - permissions violation PGD 7a523067 P4D 7a523067 PUD 7a528067 PMD 7a525067 PTE 800000007048f867 Oops: 0003 [#1] PREEMPT SMP NOPTI CPU: 0 PID: 468 Comm: cp Not tainted 5.15.0+ #6 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-27-g64f37cc530f1-prebuilt.qemu.org 04/01/2014 RIP: 0010:readfromoldmem.part.0.cold+0x1d/0x86 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 <49> c7 45 00 00 00 00 00 49 c7 44 05 f8 00 00 00 00 48 83 e7 f81 RSP: 0018:ffffc9000073be08 EFLAGS: 00010212 RAX: 0000000000001000 RBX: 00000000002fd000 RCX: 00007f2374e01000 RDX: 0000000000000001 RSI: 00000000ffffdfff RDI: 00007f2374e01008 RBP: 0000000000001000 R08: 0000000000000000 R09: ffffc9000073bc50 R10: ffffc9000073bc48 R11: ffffffff829461a8 R12: 000000000000f000 R13: 00007f2374e01000 R14: 0000000000000000 R15: ffff88807bd421e8 FS: 00007f2374e12140(0000) GS:ffff88807f000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f2374e01000 CR3: 000000007a4aa000 CR4: 0000000000350eb0 Call Trace: readvmcore+0x236/0x2c0 procregread+0x55/0xa0 vfsread+0x95/0x190 ksysread+0x4f/0xc0 dosyscall64+0x3b/0x90 entrySYSCALL64afterhwframe+0x44/0xae
Some x86-64 CPUs have a CPU feature called "Supervisor Mode Access Prevention (SMAP)", which is used to detect wrong access from the kernel to user buffers like this: SMAP triggers a permissions violation on wrong access. In the x86-64 variant of clearuser(), SMAP is properly handled via clac()+stac().
To fix, properly use clearuser() when we're dealing with a user buffer.
— NVD
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2021-47566?
CVE-2021-47566 has a severity rating that indicates it could potentially lead to memory corruption issues in the Linux kernel.
How do I fix CVE-2021-47566?
To fix CVE-2021-47566, you should upgrade to the latest patched version of the Linux kernel as specified in the advisory.
Which versions of the Linux kernel are affected by CVE-2021-47566?
CVE-2021-47566 affects multiple versions of the Linux kernel prior to 4.4.294, 4.9.292, 4.14.257, 4.19.219, 5.4.163, 5.10.83, 5.15.6, and 5.16.
Who is responsible for addressing CVE-2021-47566?
The Linux kernel CVE team is responsible for addressing CVE-2021-47566 and ensuring that the vulnerability is resolved in future kernel updates.
What potential impact does CVE-2021-47566 have on systems?
CVE-2021-47566 could lead to unauthorized access or manipulation of kernel memory, which may compromise system integrity and security.