CVE-2025-21879

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

btrfs: fix use-after-free on inode when scanning root during em shrinking

At btrfs_scan_root() we are accessing the inodes root (and fs_info) in a call to btrfs_fs_closing() after we have scheduled the inode for a delayed iput, and that can result in a use-after-free on the inode in case the cleaner kthread does the iput before we dereference the inode in the call to btrfs_fs_closing().

Fix this by using the fs_info stored already in a local variable instead of doing inode->root->fs_info.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/07836bc18f4ae42da4e922244f4685561c18755e
• https://git.kernel.org/stable/c/59f37036bb7ab3d554c24abc856aabca01126414
• https://git.kernel.org/stable/c/5e79d26014f9386387575b9ed60d342057cee49b