CVE-2021-47337

MEDIUM
Published May 21, 2024 Modified Dec 24, 2024 CWE-476

Description

In the Linux kernel, the following vulnerability has been resolved: scsi: core: Fix bad pointer dereference when ehandler kthread is invalid Commit 66a834d09293 ("scsi: core: Fix error handling of scsi_host_alloc()") changed the allocation logic to call put_device() to perform host cleanup with the assumption that IDA removal and stopping the kthread would properly be performed in scsi_host_dev_release(). However, in the unlikely case that the error handler thread fails to spawn, shost->ehandler is set to ERR_PTR(-ENOMEM). The error handler cleanup code in scsi_host_dev_release() will call kthread_stop() if shost->ehandler != NULL which will always be the case whether the kthread was successfully spawned or not. In the case that it failed to spawn this has the nasty side effect of trying to dereference an invalid pointer when kthread_stop() is called. The following splat provides an example of this behavior in the wild: scsi host11: error handler thread failed to spawn, error = -4 Kernel attempted to read user page (10c) - exploit attempt? (uid: 0) BUG: Kernel NULL pointer dereference on read at 0x0000010c Faulting instruction address: 0xc00000000818e9a8 Oops: Kernel access of bad area, sig: 11 [#1] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries Modules linked in: ibmvscsi(+) scsi_transport_srp dm_multipath dm_mirror dm_region hash dm_log dm_mod fuse overlay squashfs loop CPU: 12 PID: 274 Comm: systemd-udevd Not tainted 5.13.0-rc7 #1 NIP: c00000000818e9a8 LR: c0000000089846e8 CTR: 0000000000007ee8 REGS: c000000037d12ea0 TRAP: 0300 Not tainted (5.13.0-rc7) MSR: 800000000280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 28228228 XER: 20040001 CFAR: c0000000089846e4 DAR: 000000000000010c DSISR: 40000000 IRQMASK: 0 GPR00: c0000000089846e8 c000000037d13140 c000000009cc1100 fffffffffffffffc GPR04: 0000000000000001 0000000000000000 0000000000000000 c000000037dc0000 GPR08: 0000000000000000 c000000037dc0000 0000000000000001 00000000fffff7ff GPR12: 0000000000008000 c00000000a049000 c000000037d13d00 000000011134d5a0 GPR16: 0000000000001740 c0080000190d0000 c0080000190d1740 c000000009129288 GPR20: c000000037d13bc0 0000000000000001 c000000037d13bc0 c0080000190b7898 GPR24: c0080000190b7708 0000000000000000 c000000033bb2c48 0000000000000000 GPR28: c000000046b28280 0000000000000000 000000000000010c fffffffffffffffc NIP [c00000000818e9a8] kthread_stop+0x38/0x230 LR [c0000000089846e8] scsi_host_dev_release+0x98/0x160 Call Trace: [c000000033bb2c48] 0xc000000033bb2c48 (unreliable) [c0000000089846e8] scsi_host_dev_release+0x98/0x160 [c00000000891e960] device_release+0x60/0x100 [c0000000087e55c4] kobject_release+0x84/0x210 [c00000000891ec78] put_device+0x28/0x40 [c000000008984ea4] scsi_host_alloc+0x314/0x430 [c0080000190b38bc] ibmvscsi_probe+0x54/0xad0 [ibmvscsi] [c000000008110104] vio_bus_probe+0xa4/0x4b0 [c00000000892a860] really_probe+0x140/0x680 [c00000000892aefc] driver_probe_device+0x15c/0x200 [c00000000892b63c] device_driver_attach+0xcc/0xe0 [c00000000892b740] __driver_attach+0xf0/0x200 [c000000008926f28] bus_for_each_dev+0xa8/0x130 [c000000008929ce4] driver_attach+0x34/0x50 [c000000008928fc0] bus_add_driver+0x1b0/0x300 [c00000000892c798] driver_register+0x98/0x1a0 [c00000000810eb60] __vio_register_driver+0x80/0xe0 [c0080000190b4a30] ibmvscsi_module_init+0x9c/0xdc [ibmvscsi] [c0000000080121d0] do_one_initcall+0x60/0x2d0 [c000000008261abc] do_init_module+0x7c/0x320 [c000000008265700] load_module+0x2350/0x25b0 [c000000008265cb4] __do_sys_finit_module+0xd4/0x160 [c000000008031110] system_call_exception+0x150/0x2d0 [c00000000800d35c] system_call_common+0xec/0x278 Fix this be nulling shost->ehandler when the kthread fails to spawn.

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CVSS v3.1 Score

5.5
MEDIUM
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-476 CWE-476

Affected Products

Vendor Product
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel

References

Advisories & Patches

https://git.kernel.org/stable/c/887bfae2732b5b02a86a859fd239d34f7ff93c05 https://git.kernel.org/stable/c/8e4212ecf0713dd57d0e3209a66201da582149b1 https://git.kernel.org/stable/c/93aa71ad7379900e61c8adff6a710a4c18c7c99b https://git.kernel.org/stable/c/c1671d2d2ef8a84837eea1b4d99ca0c6a66fb691 https://git.kernel.org/stable/c/d2f0b960d07e52bb664471b4de0ed8b08c636b3a https://git.kernel.org/stable/c/e1bd3fac2baa3d5c04375980c1d5263a3335af92 https://git.kernel.org/stable/c/ea518b70ed5e4598c8d706f37fc16f7b06e440bd https://git.kernel.org/stable/c/f3d0a109240c9bed5c60d819014786be3a2fe515 https://git.kernel.org/stable/c/887bfae2732b5b02a86a859fd239d34f7ff93c05 https://git.kernel.org/stable/c/8e4212ecf0713dd57d0e3209a66201da582149b1 https://git.kernel.org/stable/c/93aa71ad7379900e61c8adff6a710a4c18c7c99b https://git.kernel.org/stable/c/c1671d2d2ef8a84837eea1b4d99ca0c6a66fb691 https://git.kernel.org/stable/c/d2f0b960d07e52bb664471b4de0ed8b08c636b3a https://git.kernel.org/stable/c/e1bd3fac2baa3d5c04375980c1d5263a3335af92 https://git.kernel.org/stable/c/ea518b70ed5e4598c8d706f37fc16f7b06e440bd https://git.kernel.org/stable/c/f3d0a109240c9bed5c60d819014786be3a2fe515

Frequently Asked Questions

What is CVE-2021-47337? +
In the Linux kernel, the following vulnerability has been resolved: scsi: core: Fix bad pointer dereference when ehandler kthread is invalid Commit 66a834d09293 ("scsi: core: Fix error handling of scsi_host_alloc()") changed the allocation logic to call put_device() to perform host cleanup with the assumption that IDA removal and stopping the kthread would properly be performed in scsi_host_dev_release(). However, in the unlikely case that the error handler thread fails to spawn, shost->ehandler is set to ERR_PTR(-ENOMEM). The error handler cleanup code in scsi_host_dev_release() will call kthread_stop() if shost->ehandler != NULL which will always be the case whether the kthread was successfully spawned or not. In the case that it failed to spawn this has the nasty side effect of trying to dereference an invalid pointer when kthread_stop() is called. The following splat provides an example of this behavior in the wild: scsi host11: error handler thread failed to spawn, error = -4 Kernel attempted to read user page (10c) - exploit attempt? (uid: 0) BUG: Kernel NULL pointer dereference on read at 0x0000010c Faulting instruction address: 0xc00000000818e9a8 Oops: Kernel access of bad area, sig: 11 [#1] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries Modules linked in: ibmvscsi(+) scsi_transport_srp dm_multipath dm_mirror dm_region hash dm_log dm_mod fuse overlay squashfs loop CPU: 12 PID: 274 Comm: systemd-udevd Not tainted 5.13.0-rc7 #1 NIP: c00000000818e9a8 LR: c0000000089846e8 CTR: 0000000000007ee8 REGS: c000000037d12ea0 TRAP: 0300 Not tainted (5.13.0-rc7) MSR: 800000000280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 28228228 XER: 20040001 CFAR: c0000000089846e4 DAR: 000000000000010c DSISR: 40000000 IRQMASK: 0 GPR00: c0000000089846e8 c000000037d13140 c000000009cc1100 fffffffffffffffc GPR04: 0000000000000001 0000000000000000 0000000000000000 c000000037dc0000 GPR08: 0000000000000000 c000000037dc0000 0000000000000001 00000000fffff7ff GPR12: 0000000000008000 c00000000a049000 c000000037d13d00 000000011134d5a0 GPR16: 0000000000001740 c0080000190d0000 c0080000190d1740 c000000009129288 GPR20: c000000037d13bc0 0000000000000001 c000000037d13bc0 c0080000190b7898 GPR24: c0080000190b7708 0000000000000000 c000000033bb2c48 0000000000000000 GPR28: c000000046b28280 0000000000000000 000000000000010c fffffffffffffffc NIP [c00000000818e9a8] kthread_stop+0x38/0x230 LR [c0000000089846e8] scsi_host_dev_release+0x98/0x160 Call Trace: [c000000033bb2c48] 0xc000000033bb2c48 (unreliable) [c0000000089846e8] scsi_host_dev_release+0x98/0x160 [c00000000891e960] device_release+0x60/0x100 [c0000000087e55c4] kobject_release+0x84/0x210 [c00000000891ec78] put_device+0x28/0x40 [c000000008984ea4] scsi_host_alloc+0x314/0x430 [c0080000190b38bc] ibmvscsi_probe+0x54/0xad0 [ibmvscsi] [c000000008110104] vio_bus_probe+0xa4/0x4b0 [c00000000892a860] really_probe+0x140/0x680 [c00000000892aefc] driver_probe_device+0x15c/0x200 [c00000000892b63c] device_driver_attach+0xcc/0xe0 [c00000000892b740] __driver_attach+0xf0/0x200 [c000000008926f28] bus_for_each_dev+0xa8/0x130 [c000000008929ce4] driver_attach+0x34/0x50 [c000000008928fc0] bus_add_driver+0x1b0/0x300 [c00000000892c798] driver_register+0x98/0x1a0 [c00000000810eb60] __vio_register_driver+0x80/0xe0 [c0080000190b4a30] ibmvscsi_module_init+0x9c/0xdc [ibmvscsi] [c0000000080121d0] do_one_initcall+0x60/0x2d0 [c000000008261abc] do_init_module+0x7c/0x320 [c000000008265700] load_module+0x2350/0x25b0 [c000000008265cb4] __do_sys_finit_module+0xd4/0x160 [c000000008031110] system_call_exception+0x150/0x2d0 [c00000000800d35c] system_call_common+0xec/0x278 Fix this be nulling shost->ehandler when the kthread fails to spawn. It has a CVSS v3.1 base score of 5.5 (MEDIUM).
How severe is CVE-2021-47337? +
CVE-2021-47337 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.
What products are affected by CVE-2021-47337? +
CVE-2021-47337 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.
How do I check if I'm vulnerable to CVE-2021-47337? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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