CVE-2026-64451 (GCVE-0-2026-64451)

Vulnerability from cvelistv5 – Published: 2026-07-25 08:51 – Updated: 2026-08-17 04:55
VLAI
Title
tracing: Fix NULL pointer dereference in func_set_flag()
Summary
In the Linux kernel, the following vulnerability has been resolved: tracing: Fix NULL pointer dereference in func_set_flag() 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.
Severity
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 76680d0d2825900f23bf35290ab2b80bdf3a8e4a , < 69f17ac132a38974cf1defb480cef6b79d1ab768 (git)
Affected: 76680d0d2825900f23bf35290ab2b80bdf3a8e4a , < c3e94604675e3db186111b8942650d86577df9b0 (git)
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Linux Linux Affected: 6.19
Unaffected: 0 , < 6.19 (semver)
Unaffected: 7.1.4 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntracing: Fix NULL pointer dereference in func_set_flag()\n\nfunc_set_flag() dereferences tr-\u003ecurrent_trace_flags before verifying\nthat the current tracer is actually the function tracer. When the active\ntracer has been switched away from \"function\" (e.g., to \"wakeup_rt\"),\ntr-\u003ecurrent_trace_flags can be NULL, leading to a NULL pointer\ndereference and kernel crash.\n\nThe call chain that triggers this is:\n\n  trace_options_write()\n    -\u003e __set_tracer_option()\n      -\u003e trace-\u003eset_flag()          /* func_set_flag */\n\nIn func_set_flag(), the first operation is:\n\n  if (!!set == !!(tr-\u003ecurrent_trace_flags-\u003eval \u0026 bit))\n\nThis dereferences tr-\u003ecurrent_trace_flags unconditionally. The safety\ncheck that guards against a non-function tracer:\n\n  if (tr-\u003ecurrent_trace != \u0026function_trace)\n      return 0;\n\nis placed *after* the dereference, which is too late.\n\nThis was observed with the following crash dump:\n\n  BUG: unable to handle page fault at 0000000000000000\n  RIP: func_set_flag+0xd\n\n  Call Trace:\n   __set_tracer_option+0x27\n   trace_options_write+0x75\n   vfs_write+0x12a\n   ksys_write+0x66\n   do_syscall_64+0x5b\n\n  RIP: ffffffff914c973d  RSP: ff67ec88b01dfdf0  RFLAGS: 00010202\n  RAX: 0000000000000000  RBX: ff3a826e80354580  RCX: 0000000000000001\n  RDX: 0000000000000001  RSI: 0000000000000000  RDI: ffffffff93918080\n\nThe disassembly confirms the fault:\n\n  func_set_flag+0:   mov 0x1f08(%rdi), %rax  ; RAX = tr-\u003ecurrent_trace_flags = NULL\n  func_set_flag+13:  mov (%rax), %eax        ; page fault: dereference NULL\n\nAt the time of the crash:\n  tr-\u003ecurrent_trace_flags = 0x0 (NULL)\n  tr-\u003ecurrent_trace = wakeup_rt_tracer (not function_trace)\n\nThe scenario is that a process opens a function tracer option file (such\nas \"func_stack_trace\"), then the current tracer is switched to another\ntracer (e.g., \"wakeup_rt\"), which sets current_trace_flags to NULL. When\nthe process subsequently writes to the option file, func_set_flag() is\ninvoked and crashes on the NULL dereference.\n\nFix this by moving the current_trace check before the\ncurrent_trace_flags dereference, so that func_set_flag() returns early\nwhen the function tracer is not active."
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntracing: Fix NULL pointer dereference in func_set_flag()\n\nfunc_set_flag() dereferences tr-\u003ecurrent_trace_flags before verifying\nthat the current tracer is actually the function tracer. When the active\ntracer has been switched away from \"function\" (e.g., to \"wakeup_rt\"),\ntr-\u003ecurrent_trace_flags can be NULL, leading to a NULL pointer\ndereference and kernel crash.\n\nThe call chain that triggers this is:\n\n  trace_options_write()\n    -\u003e __set_tracer_option()\n      -\u003e trace-\u003eset_flag()          /* func_set_flag */\n\nIn func_set_flag(), the first operation is:\n\n  if (!!set == !!(tr-\u003ecurrent_trace_flags-\u003eval \u0026 bit))\n\nThis dereferences tr-\u003ecurrent_trace_flags unconditionally. The safety\ncheck that guards against a non-function tracer:\n\n  if (tr-\u003ecurrent_trace != \u0026function_trace)\n      return 0;\n\nis placed *after* the dereference, which is too late.\n\nThis was observed with the following crash dump:\n\n  BUG: unable to handle page fault at 0000000000000000\n  RIP: func_set_flag+0xd\n\n  Call Trace:\n   __set_tracer_option+0x27\n   trace_options_write+0x75\n   vfs_write+0x12a\n   ksys_write+0x66\n   do_syscall_64+0x5b\n\n  RIP: ffffffff914c973d  RSP: ff67ec88b01dfdf0  RFLAGS: 00010202\n  RAX: 0000000000000000  RBX: ff3a826e80354580  RCX: 0000000000000001\n  RDX: 0000000000000001  RSI: 0000000000000000  RDI: ffffffff93918080\n\nThe disassembly confirms the fault:\n\n  func_set_flag+0:   mov 0x1f08(%rdi), %rax  ; RAX = tr-\u003ecurrent_trace_flags = NULL\n  func_set_flag+13:  mov (%rax), %eax        ; page fault: dereference NULL\n\nAt the time of the crash:\n  tr-\u003ecurrent_trace_flags = 0x0 (NULL)\n  tr-\u003ecurrent_trace = wakeup_rt_tracer (not function_trace)\n\nThe scenario is that a process opens a function tracer option file (such\nas \"func_stack_trace\"), then the current tracer is switched to another\ntracer (e.g., \"wakeup_rt\"), which sets current_trace_flags to NULL. When\nthe process subsequently writes to the option file, func_set_flag() is\ninvoked and crashes on the NULL dereference.\n\nFix this by moving the current_trace check before the\ncurrent_trace_flags dereference, so that func_set_flag() returns early\nwhen the function tracer is not active."
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        "id": "CVE-2026-64451",
        "lastModified": "2026-09-03T15:29:27.130",
        "metrics": {
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                "confidentialityImpact": "NONE",
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                "scope": "UNCHANGED",
                "userInteraction": "NONE",
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        "references": [
          {
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        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Analyzed",
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                "lang": "en",
                "value": "CWE-476"
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      "current_release_date": "2026-09-03T16:05:49+00:00",
      "cve": "CVE-2026-64451",
      "id": "CVE-2026-64451",
      "initial_release_date": "2026-07-25T00:00:00+00:00",
      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: tracing: Fix NULL pointer dereference in func_set_flag()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64451.json",
      "version": "3"
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}



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