# CVE-2021-47618: linux: In the Linux kernel, the following vulnerability has been resolved:  ARM: 9170/1: fix panic when kasan and kprobe are...

CVE-2021-47618 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47618, released June 20, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47618
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0024
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 20, 2024

## Description

In the Linux kernel, the following vulnerability has been resolved:  ARM: 9170/1: fix panic when kasan and kprobe are enabled  arm32 uses software to simulate the instruction replaced by kprobe. some instructions may be simulated by constructing assembly functions. therefore, before executing instruction simulation, it is necessary to construct assembly function execution environment in C language through binding registers. after kasan is enabled, the register binding relationship will be destroyed, resulting in instruction simulation errors and causing kernel panic.  the kprobe emulate instruction function is distributed in three files: actions-common.c actions-arm.c actions-thumb.c, so disable KASAN when compiling these files.  for example, use kprobe insert on cap_capable+20 after kasan enabled, the cap_capable assembly code is as follows: <cap_capable>: e92d47f0	push	{r4, r5, r6, r7, r8, r9, sl, lr} e1a05000	mov	r5, r0 e280006c	add	r0, r0, #108    ; 0x6c e1a04001	mov	r4, r1 e1a06002	mov	r6, r2 e59fa090	ldr	sl, [pc, #144]  ; ebfc7bf8	bl	c03aa4b4 <__asan_load4> e595706c	ldr	r7, [r5, #108]  ; 0x6c e2859014	add	r9, r5, #20 ...... The emulate_ldr assembly code after enabling kasan is as follows: c06f1384 <emulate_ldr>: e92d47f0	push	{r4, r5, r6, r7, r8, r9, sl, lr} e282803c	add	r8, r2, #60     ; 0x3c e1a05000	mov	r5, r0 e7e37855	ubfx	r7, r5, #16, #4 e1a00008	mov	r0, r8 e1a09001	mov	r9, r1 e1a04002	mov	r4, r2 ebf35462	bl	c03c6530 <__asan_load4> e357000f	cmp	r7, #15 e7e36655	ubfx	r6, r5, #12, #4 e205a00f	and	sl, r5, #15 0a000001	beq	c06f13bc <emulate_ldr+0x38> e0840107	add	r0, r4, r7, lsl #2 ebf3545c	bl	c03c6530 <__asan_load4> e084010a	add	r0, r4, sl, lsl #2 ebf3545a	bl	c03c6530 <__asan_load4> e2890010	add	r0, r9, #16 ebf35458	bl	c03c6530 <__asan_load4> e5990010	ldr	r0, [r9, #16] e12fff30	blx	r0 e356000f	cm	r6, #15 1a000014	bne	c06f1430 <emulate_ldr+0xac> e1a06000	mov	r6, r0 e2840040	add	r0, r4, #64     ; 0x40 ......  when running in emulate_ldr to simulate the ldr instruction, panic occurred, and the log is as follows: Unable to handle kernel NULL pointer dereference at virtual address 00000090 pgd = ecb46400 [00000090] *pgd=2e0fa003, *pmd=00000000 Internal error: Oops: 206 [#1] SMP ARM PC is at cap_capable+0x14/0xb0 LR is at emulate_ldr+0x50/0xc0 psr: 600d0293 sp : ecd63af8  ip : 00000004  fp : c0a7c30c r10: 00000000  r9 : c30897f4  r8 : ecd63cd4 r7 : 0000000f  r6 : 0000000a  r5 : e59fa090  r4 : ecd63c98 r3 : c06ae294  r2 : 00000000  r1 : b7611300  r0 : bf4ec008 Flags: nZCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment user Control: 32c5387d  Table: 2d546400  DAC: 55555555 Process bash (pid: 1643, stack limit = 0xecd60190) (cap_capable) from (kprobe_handler+0x218/0x340) (kprobe_handler) from (kprobe_trap_handler+0x24/0x48) (kprobe_trap_handler) from (do_undefinstr+0x13c/0x364) (do_undefinstr) from (__und_svc_finish+0x0/0x30) (__und_svc_finish) from (cap_capable+0x18/0xb0) (cap_capable) from (cap_vm_enough_memory+0x38/0x48) (cap_vm_enough_memory) from (security_vm_enough_memory_mm+0x48/0x6c) (security_vm_enough_memory_mm) from (copy_process.constprop.5+0x16b4/0x25c8) (copy_process.constprop.5) from (_do_fork+0xe8/0x55c) (_do_fork) from (SyS_clone+0x1c/0x24) (SyS_clone) from (__sys_trace_return+0x0/0x10) Code: 0050a0e1 6c0080e2 0140a0e1 0260a0e1 (f801f0e7)

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.16.7-1 | [DEBIAN-CVE-2021-47618](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47618.md) | Jun 20, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.16.7-1 | [DEBIAN-CVE-2021-47618](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47618.md) | Jun 20, 2024 |
| Linux | linux Debian 14 | 5.16.7-1 | [DEBIAN-CVE-2021-47618](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47618.md) | Jun 20, 2024 |

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