blk-cgroup: fix UAF in __blkcg_rstat_flush()

Answer in brief

CVE-2026-63802 records a High severity (CVSS 7.8) vulnerability in blk-cgroup: fix UAF in __blkcg_rstat_flush(). The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Jul 19, 2026Updated Aug 17, 2026Source checked Sep 20, 2026First seen by HOL Aug 5, 2026Material review Aug 17, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.8
Exploitation: Not marked as known exploited
Affected software: 5 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 7.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Affected products and reported versions
Product	Affected versions	Fixed versions
cpe:2.3:o:linux:linux_kernel::::::::	Not reported	Not reported
cpe:2.3:o:linux:linux_kernel:6.4:-::::::	Not reported	Not reported
cpe:2.3:o:linux:linux_kernel:6.4:rc7::::::	Not reported	Not reported

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Linux/Linuxgeneric	>=20cb1c2fb7568a6054c55defe044311397e01ddb <96e545410c4f74c89d496c1d5d9ef8d08f14368b \|\| >=20cb1c2fb7568a6054c55defe044311397e01ddb <bbebd9425cad3573d1527441753899b926525a0f \|\| >=20cb1c2fb7568a6054c55defe044311397e01ddb <5e5b7f2ef854936e95dceb6a2fdfefcb7152d2c6 \|\| >=20cb1c2fb7568a6054c55defe044311397e01ddb <afebe44facc48a61761e885bbb7f0380d4a603ec \|\| >=20cb1c2fb7568a6054c55defe044311397e01ddb <0ab5ee5a1badb58cbb2242617cb01a4972b1f2a2 \|\| 0f6090d90f627d8c58f939067d6c6821ce1b3c68 \|\| >=6.3.9 <6.4	96e545410c4f74c89d496c1d5d9ef8d08f14368b, bbebd9425cad3573d1527441753899b926525a0f, 5e5b7f2ef854936e95dceb6a2fdfefcb7152d2c6, afebe44facc48a61761e885bbb7f0380d4a603ec, 0ab5ee5a1badb58cbb2242617cb01a4972b1f2a2, 6.4
Linux/Linuxgeneric	6.4	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Linux/Linux, Linux/Linux.
Review the reported fix. Update Linux/Linux to 96e545410c4f74c89d496c1d5d9ef8d08f14368b if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Jul 19, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 17, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 5, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.