CVE-2021-4150: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-4150 is a use-after-free vulnerability discovered in the Linux kernel's block subsystem, specifically in the add_partition function in block/partitions/core.c. The vulnerability was disclosed on March 23, 2022, affecting Linux kernel versions before 5.15-rc7. The flaw occurs due to improper handling of reference counts when adding partitions to a disk (NVD).

The vulnerability stems from incorrect reference counting in the block subsystem when deviceadd call fails during partition addition to a disk. When adding partitions, the disk object's reference count is increased, but if deviceadd() returns an error, the reference count is erroneously reduced twice - once at putdevice(pdev) and again at putdisk(disk). This double decrease causes the object's life cycle to end prematurely, leading to a use-after-free condition. The vulnerability has been assigned a CVSS v3.1 base score of 5.5 (Medium) with vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (NVD).

The vulnerability allows local attackers with user privileges to cause a denial of service condition on the system by triggering a use-after-free scenario in the kernel's block subsystem. This can potentially lead to system crashes or other unspecified impacts through a crafted user space program (CVE).

The vulnerability was fixed in Linux kernel version 5.15-rc7 through a patch that modifies the addpartition function to return directly after calling putdevice(), preventing the double decrease of the reference count. The fix involves a single line change in block/partitions/core.c (LKML).