CVE-2026-64451

What the bug is

func_set_flag() dereferences tr->current_trace_flags before verifying that the current tracer is actually the function tracer. When the active tracer has been switched away from "function" (e.g., to "wakeup_rt"), tr->current_trace_flags can be NULL, leading to a NULL pointer dereference and kernel crash. The call chain that triggers this is: trace_options_write() -> __set_tracer_option() -> trace->set_flag() /* func_set_flag */ In func_set_flag(), the first operation is: if (!!set == !!(tr->current_trace_flags->val & bit)) This dereferences tr->current_trace_flags unconditionally. The safety check that guards against a non-function tracer: if (tr->current_trace != &function_trace) return 0; is placed *after* the dereference, which is too late. This was observed with the following crash dump: BUG: unable to handle page fault at 0000000000000000 RIP: func_set_flag+0xd Call Trace: __set_tracer_option+0x27 trace_options_write+0x75 vfs_write+0x12a ksys_write+0x66 do_syscall_64+0x5b RIP: ffffffff914c973d RSP: ff67ec88b01dfdf0 RFLAGS: 00010202 RAX: 0000000000000000 RBX: ff3a826e80354580 RCX: 0000000000000001 RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffffffff93918080 The disassembly confirms the fault: func_set_flag+0: mov 0x1f08(%rdi), %rax ; RAX = tr->current_trace_flags = NULL func_set_flag+13: mov (%rax), %eax ; page fault: dereference NULL At the time of the crash: tr->current_trace_flags = 0x0 (NULL) tr->current_trace = wakeup_rt_tracer (not function_trace) The scenario is that a process opens a function tracer option file (such as "func_stack_trace"), then the current tracer is switched to another tracer (e.g., "wakeup_rt"), which sets current_trace_flags to NULL. When the process subsequently writes to the option file, func_set_flag() is invoked and crashes on the NULL dereference. Fix this by moving the current_trace check before the current_trace_flags dereference, so that func_set_flag() returns early when the function tracer is not active.

Where it lives

The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.

kernel/trace/trace_functions.c

What this is

TRACINGMAINTAINERS section matched on kernel/trace/ · linux-kernel@vger.kernel.org · Maintained

Check it on the machine

grep -wE 'CONFIG_FUNCTION_TRACER|CONFIG_RETHOOK|CONFIG_RING_BUFFER|CONFIG_TRACEPOINTS|CONFIG_TRACE_CLOCK|CONFIG_TRACING' /boot/config-$(uname -r)

Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.

Show whether Debian builds this, per release

Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.

• bookwormYnot built on arm64/arm64, arm64/cloud-arm64, arm64/rt/arm64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le
• trixieYnot built on arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt/arm64, armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp
• forky, sidYnot built on arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt-arm64, armhf/armmp, armhf/armmp-lpae

Y

built in where it is built at all; some flavours do not build it

Build switches

CONFIG_FUNCTION_TRACER, CONFIG_RETHOOK, CONFIG_RING_BUFFER, CONFIG_TRACEPOINTS, CONFIG_TRACE_CLOCK, CONFIG_TRACING

Reads as

all on means the file is compiled; any one off means it is not.

From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages

Signals

Published

2026-07-25 (3 months ago)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

0.14%, higher than 3.2% of all CVEssource

CISA KEV

not listedthe KEV catalogue

Debian urgency

unimportantsource

Subsystem

kernel/trace

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
6.19	7.1.4	69f17ac132a3
6.19	7.2	c3e94604675e