What’s Vulnerable › Vulnerabilities

CVE-2024-50217: btrfs: fix use-after-free of block device file in __btrfs_free_extra_devids()

• Severity: high (CVSS 7.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2024-11-09 · updated 2026-08-04
• Weakness: CWE-416

Description

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix use-after-free of block device file in __btrfs_free_extra_devids() Mounting btrfs from two images (which have the same one fsid and two different dev_uuids) in certain executing order may trigger an UAF for variable 'device->bdev_file' in __btrfs_free_extra_devids(). And following are the details: 1. Attach image_1 to loop0, attach image_2 to loop1, and scan btrfs devices by ioctl(BTRFS_IOC_SCAN_DEV): / btrfs_device_1 → loop0 fs_device \ btrfs_device_2 → loop1 2. mount /dev/loop0 /mnt btrfs_open_devices btrfs_device_1->bdev_file = btrfs_get_bdev_and_sb(loop0) btrfs_device_2->bdev_file = btrfs_get_bdev_and_sb(loop1) btrfs_fill_super open_ctree fail: btrfs_close_devices // -ENOMEM btrfs_close_bdev(btrfs_device_1) fput(btrfs_device_1->bdev_file) // btrfs_device_1->bdev_file is freed btrfs_close_bdev(btrfs_device_2) fput(btrfs_device_2->bdev_file) 3. mount /dev/loop1 /mnt btrfs_open_devices btrfs_get_bdev_and_sb(&bdev_file) // EIO, btrfs_device_1->bdev_file is not assigned, // which points to a freed memory area btrfs_device_2->bdev_file = btrfs_get_bdev_and_sb(loop1) btrfs_fill_super open_ctree btrfs_free_extra_devids if (btrfs_device_1->bdev_file) fput(btrfs_device_1->bdev_file) // UAF ! Fix it by setting 'device->bdev_file' as 'NULL' after closing the btrfs_device in btrfs_close_one_device().

Affected products

• Linux kernel: from 4.8 before 6.11.7; 6.12-rc1, 6.12-rc2, 6.12-rc3, 6.12-rc4, 6.12-rc5 — fixed in 6.11.7

How to fix

Upgrade to a fixed version: Linux kernel 6.11.7. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/47a83f8df39545f3f552bb6a1b6d9c30e37621dd
• https://git.kernel.org/stable/c/aec8e6bf839101784f3ef037dcdb9432c3f32343
• http://www.openwall.com/lists/oss-security/2025/04/10/4
• http://www.openwall.com/lists/oss-security/2025/04/10/5
• http://www.openwall.com/lists/oss-security/2025/04/10/6

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