CVE-2009-3726

Published Nov 9, 2009

Last updated 6 months ago

Overview

Description
The nfs4_proc_lock function in fs/nfs/nfs4proc.c in the NFSv4 client in the Linux kernel before 2.6.31-rc4 allows remote NFS servers to cause a denial of service (NULL pointer dereference and panic) by sending a certain response containing incorrect file attributes, which trigger attempted use of an open file that lacks NFSv4 state.
Source
secalert@redhat.com
NVD status
Modified
Products
linux_kernel

Risk scores

CVSS 2.0

Type
Primary
Base score
7.8
Impact score
6.9
Exploitability score
10
Vector string
AV:N/AC:L/Au:N/C:N/I:N/A:C

Weaknesses

nvd@nist.gov
CWE-399

Social media

Hype score
Not currently trending

Vendor comments

  • Red HatRed Hat is aware of this issue and is tracking it via the following bug: https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=CVE-2009-3726. The Linux kernel as shipped with Red Hat Enterprise Linux 3 did not have support for NFSv4, and therefore is not affected by this issue. It was addressed in Red Hat Enterprise Linux 5, and Red Hat Enterprise MRG via https://rhn.redhat.com/errata/RHSA-2009-1670.html and https://rhn.redhat.com/errata/RHSA-2009-1635.html respectively. A future kernel update in Red Hat Enterprise Linux 4 will address this issue.

Configurations

  1. In the Linux kernel, the following vulnerability has been resolved: cgroup: Avoid iteration of dying tasks with zero refcount The commit 260fbcb92bbea ("cgroup: Move dying_tasks cleanup from cgroup_task_release() to cgroup_task_free()") extended the lifetime of tasks on the dying_tasks list. The iterators have provision to go through dying_tasks because of dying threadgroup leaders or explicit CSS_TASK_ITER_WITH_DEAD, however, it was expected that such tasks can obtain a new reference (that is possible before cgroup_task_release()/put_task_struct_rcu_user()). The tasks after cgroup_task_release() and before cgroup_task_free() are subject to race when they may or may not have ->usage count > 0. The race window is between css_task_iter_next() invocations when css_set_lock is released and we may arrive at a new ->task_pos. The iterator should not attempt to resurrect tasks whose ->usage count dropped to zero. (When that happens, __put_task_struct_rcu_cb() is already imminent and the returned task_struct would could be used after free.) As for the fix, we cannot simply check the signal->live count of a task on the dying list because that won't distinguish regular zombies waiting to be reaped from RCU remnant tasks that are going to be free'd. Therefore add an extra check to rule out ->usage==0 tasks from any iteration. The repeat: loop in css_task_iter_advance() doesn't consider ->usage count, so add a new loop to css_task_iter_next() to skip de-used tasks on the dying_list. Rough illustration of the possible race R (reader of cgroup.procs) T (thread) L (group leader) --------------------------------- -------------------------------- -------------------------------- L exits, signal->live > 0 cgroup_task_dead(L) css_set_skip_task_iters() // skips only cset->tasks list_add_tail(&L->cg_list, &cset->dying_tasks) css_task_iter_next() take css_set_lock css_task_iter_advance() leader && signal->live != 0 => it->task_pos = &L->cg_list release css_set_lock T exits --signal->live == 0 cgroup_task_dead(T) // css_set_lock release_task(T) cgroup_task_release(T) release_task(L) // zap_leader cgroup_task_release(L) put_task_struct_rcu_user(L) ...RCU... put_task_struct(L) L->usage = 0 /* L still on dying_tasks */ ...RCU... __put_task_struct(L) css_task_iter_next() // another iteration take css_set_lock it->task_pos = &L->cg_list get_task_struct(L) => addition on 0 drop css_set_lock cgroup_task_free(L) css_set_skip_task_iters() // dying skip comes too late free_task(L) cgroup_procs_show() task_pid_vnr(L)•CVE-2026-98163

References

Sources include official advisories and independent security research.