CVE-2024-50273: btrfs: reinitialize delayed ref list after deleting it from the list

Severity: medium (CVSS 5.5 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: 2024-11-19 · updated 2026-08-04
Weakness: CWE-908

Description

In the Linux kernel, the following vulnerability has been resolved: btrfs: reinitialize delayed ref list after deleting it from the list At insert_delayed_ref() if we need to update the action of an existing ref to BTRFS_DROP_DELAYED_REF, we delete the ref from its ref head's ref_add_list using list_del(), which leaves the ref's add_list member not reinitialized, as list_del() sets the next and prev members of the list to LIST_POISON1 and LIST_POISON2, respectively. If later we end up calling drop_delayed_ref() against the ref, which can happen during merging or when destroying delayed refs due to a transaction abort, we can trigger a crash since at drop_delayed_ref() we call list_empty() against the ref's add_list, which returns false since the list was not reinitialized after the list_del() and as a consequence we call list_del() again at drop_delayed_ref(). This results in an invalid list access since the next and prev members are set to poison pointers, resulting in a splat if CONFIG_LIST_HARDENED and CONFIG_DEBUG_LIST are set or invalid poison pointer dereferences otherwise. So fix this by deleting from the list with list_del_init() instead.

Affected products

Linux kernel: from 4.10 before 4.19.324; from 4.20 before 5.4.286; from 5.5 before 5.10.230; from 5.11 before 5.15.172; from 5.16 before 6.1.117; from 6.2 before 6.6.61 — fixed in 4.19.324, 5.10.230, 5.15.172, 5.4.286, 6.1.117, 6.11.8

How to fix

Upgrade to a fixed version: Linux kernel 4.19.324, 5.10.230, 5.15.172, 5.4.286. Check the vendor advisory for mitigations.

References

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