Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

ext4: fix mb_cache_entry's e_refcnt leak in ext4_xattr_block_cache_find()

Syzbot reports a warning as follows:

============================================ WARNING: CPU: 0 PID: 5075 at fs/mbcache.c:419 mb_cache_destroy+0x224/0x290 Modules linked in: CPU: 0 PID: 5075 Comm: syz-executor199 Not tainted 6.9.0-rc6-gb947cc5bf6d7 RIP: 0010:mb_cache_destroy+0x224/0x290 fs/mbcache.c:419 Call Trace: <TASK> ext4_put_super+0x6d4/0xcd0 fs/ext4/super.c:1375 generic_shutdown_super+0x136/0x2d0 fs/super.c:641 kill_block_super+0x44/0x90 fs/super.c:1675 ext4_kill_sb+0x68/0xa0 fs/ext4/super.c:7327 [...] ============================================

This is because when finding an entry in ext4_xattr_block_cache_find(), if ext4_sb_bread() returns -ENOMEM, the ce's e_refcnt, which has already grown in the __entry_find(), won't be put away, and eventually trigger the above issue in mb_cache_destroy() due to reference count leakage.

So call mb_cache_entry_put() on the -ENOMEM error branch as a quick fix.

Affected: Ubuntu:Pro:18.04:LTS: linux-aws-5.4, Ubuntu:Pro:18.04:LTS: linux-gcp-5.4, Ubuntu:Pro:18.04:LTS: linux-hwe-5.4, Ubuntu:Pro:18.04:LTS: linux-ibm-5.4, Ubuntu:20.04:LTS: linux, Ubuntu:20.04:LTS: linux-aws, Ubuntu:20.04:LTS: linux-gcp, Ubuntu:20.04:LTS: linux-gkeop, Ubuntu:20.04:LTS: linux-ibm, Ubuntu:20.04:LTS: linux-iot and 3 more

Several security issues were discovered in the Linux kernel. An attacker could possibly use these to compromise the system. This update corrects flaws in the following subsystems: - ARM64 architecture; - M68K architecture; - User-Mode Linux (UML); - x86 architecture; - Accessibility subsystem; - Character device driver; - Clock framework and drivers; - CPU frequency scaling framework; - Hardware crypto device drivers; - Buffer Sharing and Synchronization framework; - FireWire subsystem; - GPU drivers; - HW tracing; - Macintosh device drivers; - Multiple devices driver; - Media drivers; - Network drivers; - Pin controllers subsystem; - S/390 drivers; - SCSI drivers; - SoundWire subsystem; - Greybus lights staging drivers; - TTY drivers; - Framebuffer layer; - Virtio drivers; - 9P distributed file system; - eCrypt file system; - EROFS file system; - Ext4 file system; - F2FS file system; - JFFS2 file system; - Network file system client; - NILFS2 file system; - SMB network file system; - Kernel debugger infrastructure; - IRQ subsystem; - Tracing infrastructure; - Dynamic debug library; - 9P file system network protocol; - Bluetooth subsystem; - Networking core; - IPv4 networking; - IPv6 networking; - Netfilter; - NET/ROM layer; - NFC subsystem; - NSH protocol; - Open vSwitch; - Phonet protocol; - TIPC protocol; - Unix domain sockets; - Wireless networking; - eXpress Data Pa…