Linux 5.4.72 Kernel Release Notes
Linux 5.4.72 is a stable kernel update containing 23 commits and approximately 126,508 lines of code changes compared to the base 5.4 release. This release focuses on critical security and stability fixes across cryptography, filesystem, USB, Bluetooth, and architecture-specific code paths.
Cryptography and Security Fixes
QAT cipher validation
Added length validation for AEAD AES-CBC-HMAC operations in the Intel QuickAssist Technology driver. The fix returns EINVAL for authenc(hmac(sha1),cbc(aes)), authenc(hmac(sha256),cbc(aes)), and authenc(hmac(sha512),cbc(aes)) when the cipher length is not a multiple of the AES block size. This prevents undefined device behavior on malformed input.
Broadcom SPU crypto validation
The Broadcom SPU driver’s GCM/CCM setkey function now properly validates key length before copying and salt manipulation. The fix ensures the key is at least as long as the salt, preventing buffer overflows and crashes from crafted input.
Bluetooth encryption security
Bluetooth connections now disconnect if E0 encryption is negotiated for Level 4 security requirements. Per the Bluetooth 5.2 specification, Level 4 requires FIPS-approved algorithms only; E0 is explicitly disallowed. The kernel now enforces this requirement and terminates the connection if a remote device attempts E0 encryption at this level.
Filesystem Fixes
ReiserFS crash prevention
Two critical reiserfs fixes address crashes during mount operations with specially crafted filesystem images:
- Fixed an oops when reiserfs attempts to verify XATTR_ROOT directory lookup. The xattr code would recurse back during ACL permission checks, causing a crash. The fix bails from
reiserfs_xattr_get()if xattrs are not yet initialized. - Fixed improper inode key initialization in
reiserfs_read_locked_inode(). The code now uses the_make_cpu_key()macro to properly initialize all key members, preventing uninitialized memory access.
USB and Device Support
USB serial driver updates
Several USB device ID additions improve hardware compatibility:
- ftdi_sio: Added support for FreeCalypso JTAG+UART adapters based on FT2232, allowing proper ttyUSB device creation for Channel B while preventing bogus device creation for JTAG channel A.
- pl2303: Added support for HP LD381 devices using the pl2303GC chipset.
- option: Added Telit FT980-KS device composition (0x1054) with rndis, diag, adb, nmea, and dual modem channels.
- option: Added Cellient MPL200 card device IDs.
USB endpoint validation
The staging comedi driver now validates the wMaxPacketSize field of discovered USB endpoints. A value of 0 is rejected as invalid, preventing potential issues with devices that incorrectly report zero-sized endpoints.
Media device refcounting
Fixed incorrect refcounting logic in the usbtv driver that could cause premature device freeing. The fix properly distinguishes between V4L and USB refcounting in error handling paths.
Bluetooth Subsystem Improvements
Connection state management
Fixed a regression in hci_encrypt_cfm() that caused incorrect connection state updates. The condition for updating connection state was inverted—the status should be updated only when no status is currently set. This fixes connection state flapping issues reported with Bluetooth headsets.
Encryption handling consolidation
The hci_encrypt_cfm() function now consolidates encryption handling by calling hci_connect_cfm() when the connection state is BT_CONFIG, simplifying caller logic.
L2CAP channel filtering
L2CAP channels that aren’t socket-based (such as A2MP channels) no longer invoke sk_filter(), which would crash due to accessing invalid socket pointers. A new callback mechanism allows channels to implement their own filtering logic if needed.
A2MP protocol fixes
Fixed uninitialized stack variables in A2MP protocol handlers that could cause unpredictable behavior with AMP controller management messages.
Bluetooth settings validation
The MGMT subsystem now correctly checks if BT_HS (Bluetooth High Speed) is enabled before reporting it as supported, preventing exposure of unsupported features to userspace.
Architecture and Build Fixes
ARM build tooling
The ARM architecture now uses the proper $(NM) variable instead of hardcoded $(CROSS_COMPILE)nm, enabling builds with alternative toolchains like LLVM’s llvm-nm. This fixes build failures when the nm executable is explicitly overridden.
ACPI event device
The ACPI Generic Event Device (GED) driver is now always built in rather than conditionally compiled for reduced hardware platforms. This allows dynamic detection of hardware-reduced platforms on systems supporting both fixed and reduced ACPI modes.
Storage and Filesystem Management
Btrfs block group read-only handling
Fixed inc_block_group_ro() to account for metadata overcommit when determining if a block group can be marked read-only. The previous logic only worked for data; metadata would almost always fail the check due to intentional overcommitment. The fix exports btrfs_can_overcommit() and checks if sufficient space exists to absorb the block group’s remaining free space.
Btrfs space calculation
Simplified space overcommit checks by removing the unnecessary system_chunk parameter from can_overcommit(). The function can determine space info type directly from flags, reducing complexity and potential bugs.
Performance Analysis Tools
Perf cs-etm variable scoping
Moved the traceid_list global variable definition from the header file cs-etm.h to cs-etm.c. Multiple inclusions of the header file could trigger compiler warnings or errors about multiple definitions. This follows proper C practices for global variable scope.
Building and Testing
To build kernel 5.4.72, download the source from the Linux kernel repository or linux-stable tree. The release was tested by the Linux Kernel Functional Testing (LKFT) project, Nvidia, and other kernel maintainers.
For production deployments, verify that your hardware and drivers are compatible with this release and test thoroughly in non-critical environments before rolling out system-wide.