CVE-2024-49870 cachefiles: fix dentry leak in cachefiles_open_file()
A race condition in the Linux kernel cachefiles module causes a dentry leak, leading to a kernel warning and potential denial of service during unmount operations.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2024-49870?
CVE-2024-49870 is a medium-severity denial of service vulnerability in Linux kernel, published on 21 Oct 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
cachefiles: fix dentry leak in cachefiles_open_file()
A dentry leak may be caused when a lookup cookie and a cull are concurrent:
P1 | P2 ----------------------------------------------------------- cachefiles_lookup_cookie cachefiles_look_up_object lookup_one_positive_unlocked // get dentry cachefiles_cull inode->i_flags |= S_KERNEL_FILE; cachefiles_open_file cachefiles_mark_inode_in_use __cachefiles_mark_inode_in_use can_use = false if (!(inode->i_flags & S_KERNEL_FILE)) can_use = true return false return false // Returns an error but doesn't put dentry
After that the following WARNING will be triggered when the backend folder is umounted:
================================================================== BUG: Dentry 000000008ad87947{i=7a,n=Dx_1_1.img} still in use (1) [unmount of ext4 sda] WARNING: CPU: 4 PID: 359261 at fs/dcache.c:1767 umount_check+0x5d/0x70 CPU: 4 PID: 359261 Comm: umount Not tainted 6.6.0-dirty #25 RIP: 0010:umount_check+0x5d/0x70 Call Trace: <TASK> d_walk+0xda/0x2b0 do_one_tree+0x20/0x40 shrink_dcache_for_umount+0x2c/0x90 generic_shutdown_super+0x20/0x160 kill_block_super+0x1a/0x40 ext4_kill_sb+0x22/0x40 deactivate_locked_super+0x35/0x80 cleanup_mnt+0x104/0x160 ==================================================================
Whether cachefiles_open_file() returns true or false, the reference count obtained by lookup_positive_unlocked() in cachefiles_look_up_object() should be released.
Therefore release that reference count in cachefiles_look_up_object() to fix the above issue and simplify the code.
Weakness: CWE-401
Which versions are affected by CVE-2024-49870?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-49870?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2024-49870 being exploited?
There is no known exploitation of CVE-2024-49870 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2024-49870, DEBIAN-CVE-2024-49870, GHSA-rvgw-688x-x595, ROOT-OS-UBUNTU-2204-CVE-2024-49870, UBUNTU-CVE-2024-49870.