Overview
About vulnerability
In the Linux kernel, the following vulnerability has been resolved:
filelock: Remove locks reliably when fcntl/close race is detected
When fcntl_setlk() races with close(), it removes the created lock with do_lock_file_wait(). However, LSMs can allow the first do_lock_file_wait() that created the lock while denying the second do_lock_file_wait() that tries to remove the lock. Separately, posix_lock_file() could also fail to remove a lock due to GFP_KERNEL allocation failure (when splitting a range in the middle).
After the bug has been triggered, use-after-free reads will occur in lock_get_status() when userspace reads /proc/locks. This can likely be used to read arbitrary kernel memory, but can’t corrupt kernel memory.
Fix it by calling locks_remove_posix() instead, which is designed to reliably get rid of POSIX locks associated with the given file and files_struct and is also used by filp_flush().
Details
- Affected product:
- AlmaLinux 9.2 ESU , CentOS 6 ELS , CentOS 7 ELS , CentOS 8.4 ELS , CentOS 8.5 ELS , CentOS Stream 8 ELS , CloudLinux 6 ELS , CloudLinux 7 ELS , Oracle Linux 6 ELS , Oracle Linux 7 ELS , RHEL 7 ELS , Ubuntu 16.04 ELS , Ubuntu 18.04 ELS
- Affected packages:
- kernel-uek @ 5.4.17 (+15 more)
In the Linux kernel, the following vulnerability has been resolved:
filelock: Remove locks reliably when fcntl/close race is detected
When fcntl_setlk() races with close(), it removes the created lock with do_lock_file_wait(). However, LSMs can allow the first do_lock_file_wait() that created the lock while denying the second do_lock_file_wait() that tries to remove the lock. Separately, posix_lock_file() could also fail to remove a lock due to GFP_KERNEL allocation failure (when splitting a range in the middle).
After the bug has been triggered, use-after-free reads will occur in lock_get_status() when userspace reads /proc/locks. This can likely be used to read arbitrary kernel memory, but can’t corrupt kernel memory.
Fix it by calling locks_remove_posix() instead, which is designed to reliably get rid of POSIX locks associated with the given file and files_struct and is also used by filp_flush().