CVE-2026-63802: blk-cgroup: fix UAF in __blkcg_rstat_flush()

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-19 · updated 2026-10-19
Weakness: CWE-416

Description

In the Linux kernel, the following vulnerability has been resolved: blk-cgroup: fix UAF in __blkcg_rstat_flush() When multiple blkgs in the same blkcg are released concurrently, a use-after-free can occur. The race happens when one blkg's __blkcg_rstat_flush() removes another blkg's iostat entries via llist_del_all(). The second blkg sees an empty list and proceeds to free itself while the first is still iterating over its entries. Move the flush from __blkg_release() (RCU callback) to blkg_release() (before call_rcu). This ensures the RCU grace period waits for any concurrent flush's rcu_read_lock() section to complete before freeing.

Affected products

Linux kernel: from 6.3.9 before 6.4; from 6.4.1 before 6.6.144; from 6.7 before 6.12.95; from 6.13 before 6.18.38; from 6.19 before 7.1.3; 6.4, 6.4-rc7 — fixed in 6.12.95, 6.18.38, 6.4, 6.6.144, 7.1.3

How to fix

Upgrade to a fixed version: Linux kernel 6.12.95, 6.18.38, 6.4, 6.6.144. Check the vendor advisory for mitigations.

References

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