Bug 2562730 (CVE-2026-99141)

Summary:	CVE-2026-99141 kernel: kernel: Denial of Service via NULL pointer dereference in tracing subsystem
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's tracing subsystem. This vulnerability allows a local user with access to tracing controls to cause a Denial of Service (DoS) by triggering a kernel crash. When switching tracers, the kernel leaves trace flags unassigned if the new tracer lacks default flags. If the trace buffer still contains records from a previous tracer, reading the trace output dereferences a null pointer.	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 2026-10-28 10:58:47 UTC

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

tracing: Fix crash in print_graph_function_event()

tracing_set_tracer() assigns the flags of the newly selected tracer
with:

	tr->current_trace_flags = t->flags ? : t->tracer->flags;

If the new tracer defines neither static flags nor default flags, like
hwlat, irqsoff or wakeup, add_tracer() has no per instance flags copy
for it, and both operands are NULL, so tr->current_trace_flags ends up
being NULL as well.

The ring buffer is not cleared when switching tracers: it is reset
inside tracer_init(), after current_trace_flags was already assigned.
If the buffer still holds function_graph entries of the previous
tracer, printing one of them dereferences the NULL pointer. This was
hit by cat trace during an ftrace stress test:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  #PF: supervisor read access in kernel mode
  RIP: 0010:print_graph_function_event+0xe/0x20
  Call Trace:
   s_show+0x4d/0x110
   seq_read_iter+0x2d4/0x490
   seq_read+0x130/0x170
   vfs_read+0xb5/0x370
   ksys_read+0x6d/0xe0
   do_syscall_64+0xbc/0x450

The snapshot buffer is not reset at all, so this can be reproduced
without a race:

  echo function_graph > /sys/kernel/tracing/current_tracer
  echo 1 > /sys/kernel/tracing/snapshot
  echo hwlat > /sys/kernel/tracing/current_tracer
  cat /sys/kernel/tracing/snapshot

Rather than teaching every user of tr->current_trace_flags about this
corner case, make sure it is never NULL: when the newly selected
tracer has no flags at all, tracing_set_tracer() falls back to a
static empty no_tracer_flags. run_tracer_selftest() can hit the same
case, so the same fallback is added there too. The existing users
already handle opts == NULL, so these tracers keep behaving as before.