{"id":"CVE-2026-64451","summary":"tracing: Fix NULL pointer dereference in func_set_flag()","details":"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 & 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 != &function_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.","modified":"2026-07-27T04:03:19.905698301Z","published":"2026-07-25T08:51:21.020Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64451.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/69f17ac132a38974cf1defb480cef6b79d1ab768"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c3e94604675e3db186111b8942650d86577df9b0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64451.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-64451"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"76680d0d2825900f23bf35290ab2b80bdf3a8e4a"},{"fixed":"69f17ac132a38974cf1defb480cef6b79d1ab768"},{"fixed":"c3e94604675e3db186111b8942650d86577df9b0"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64451.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.4"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64451.json"}}],"schema_version":"1.7.5"}