CVE-2024-50229 nilfs2: fix potential deadlock with newly created symlinks
A deadlock in the nilfs2 filesystem can cause a system hang when creating symlinks, requiring a kernel patch to resolve.
- 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-2024-50229?
CVE-2024-50229 is a medium-severity denial of service vulnerability in Linux kernel, published on 9 Nov 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:
nilfs2: fix potential deadlock with newly created symlinks
Syzbot reported that page_symlink(), called by nilfs_symlink(), triggers memory reclamation involving the filesystem layer, which can result in circular lock dependencies among the reader/writer semaphore nilfs->ns_segctor_sem, s_writers percpu_rwsem (intwrite) and the fs_reclaim pseudo lock.
This is because after commit 21fc61c73c39 ("don't put symlink bodies in pagecache into highmem"), the gfp flags of the page cache for symbolic links are overwritten to GFP_KERNEL via inode_nohighmem().
This is not a problem for symlinks read from the backing device, because the __GFP_FS flag is dropped after inode_nohighmem() is called. However, when a new symlink is created with nilfs_symlink(), the gfp flags remain overwritten to GFP_KERNEL. Then, memory allocation called from page_symlink() etc. triggers memory reclamation including the FS layer, which may call nilfs_evict_inode() or nilfs_dirty_inode(). And these can cause a deadlock if they are called while nilfs->ns_segctor_sem is held:
Fix this issue by dropping the __GFP_FS flag from the page cache GFP flags of newly created symlinks in the same way that nilfs_new_inode() and __nilfs_read_inode() do, as a workaround until we adopt nofs allocation scope consistently or improve the locking constraints.
Weakness: CWE-667
Which versions are affected by CVE-2024-50229?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-50229?
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-2024-50229 being exploited?
There is no known exploitation of CVE-2024-50229 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-53067, AZL-53124, BELL-CVE-2024-50229, DEBIAN-CVE-2024-50229, GHSA-7h5p-3h8w-5629, UBUNTU-CVE-2024-50229.