Bug 2541167 (CVE-2026-97937)

Summary:	CVE-2026-97937 kernel: ftrace: fork: Initialize function graph state before copy_exec_state()
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel. During process creation when the Function Tracer (ftrace) graph functionality is active, a memory allocation failure can lead to the kernel prematurely releasing memory still referenced by the parent process. A local attacker could exploit this use-after-free flaw to crash the system, resulting in a Denial of Service (DoS), or potentially escalate privileges.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-25 10:53:54 UTC

In the Linux kernel, the following vulnerability has been resolved:

ftrace: fork: Initialize function graph state before copy_exec_state()

dup_task_struct() copies the parent's task_struct, including ret_stack.
ftrace_graph_init_task() clears the copied function graph state, but it
currently runs after copy_exec_state().

For non-CLONE_VM forks, copy_exec_state() allocates a new task_exec_state.
If that allocation fails, copy_process() reaches bad_fork_free and
free_task() calls ftrace_graph_exit_task(). Since the child still carries
the parent's ret_stack pointer, the unwind frees the parent's active
function graph return stack. The parent subsequently accesses freed memory
from function_graph_enter_regs().

KASAN reports:

[   22.190920] ==================================================================
[   22.195899] BUG: KASAN: slab-use-after-free in function_graph_enter_regs+0xa76/0xb90
[   22.200747] Write of size 8 at addr ff110000054dc0a8 by task repro/1
[   22.205134]
[   22.210770] CPU: 0 UID: 0 PID: 1 Comm: repro Not tainted 7.2.0-07732-g9328b3b03bdc-dirty #3 PREEMPT(lazy)
[   22.212576] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[   22.213750] Call Trace:
[   22.215271]  <TASK>
[   22.216242]  ? ftrace_stub_direct_tramp+0x10/0x10
[   22.217774]  dump_stack_lvl+0x4e/0x70
[   22.220531]  print_report+0x157/0x4b4
[   22.223202]  ? fixup_red_left+0x9/0x30
[   22.224407]  ? complete_report_info+0x83/0x110
[   22.226679]  ? function_graph_enter_regs+0xa76/0xb90
[   22.228084]  kasan_report+0xce/0x100
[   22.230109]  ? function_graph_enter_regs+0xa76/0xb90
[   22.232860]  ? stack_trace_save+0x4/0xd0
[   22.234156]  function_graph_enter_regs+0xa76/0xb90
[   22.236090]  ? kasan_save_stack+0x30/0x50
[   22.237752]  ? __pfx_function_graph_enter_regs+0x10/0x10
[   22.238694]  ? ring_buffer_lock_reserve+0x345/0xf80
[   22.239628]  ? stack_trace_save+0x4/0xd0
[   22.242121]  ? stack_trace_save+0x4/0xd0
[   22.243588]  ftrace_graph_func+0xda/0x160
[   22.245362]  ? ftrace_stub_direct_tramp+0x10/0x10
[   22.246520]  0xffffffffa0000095
[   22.250528]  ? stack_trace_save+0x9/0xd0
[   22.251757]  ? ring_buffer_unlock_commit+0x11d/0x5c0
[   22.253152]  stack_trace_save+0x9/0xd0
[   22.254264]  kasan_save_stack+0x30/0x50
[   22.273631]  kasan_save_track+0x14/0x30
[   22.276763]  kasan_save_free_info+0x3b/0x70
[   22.278296]  __kasan_slab_free+0x43/0x70
[   22.280157]  kmem_cache_free+0xbf/0x3b0
[   22.282963]  ? ftrace_stub_direct_tramp+0x10/0x10
[   22.284001]  free_task+0xa2/0x160
[   22.285699]  ? ftrace_stub_direct_tramp+0x10/0x10
[   22.286752]  copy_process+0x2aae/0x7bc0

Initialize the child function graph state immediately after
dup_task_struct(), before the first fallible operation.

Comment 1 Keith Grant 2026-09-29 20:57:14 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-97937.mbox