UBUNTU-CVE-2026-97936: Null Pointer Dereference

In the Linux kernel, the following vulnerability has been resolved: tracing: Fix memory corruption from the histogram stacktrace modifier parsefield() sets HISTFIELDFLSTACKTRACE from the ".stacktrace" modifier before it looks the field name up, and nothing afterwards checks that the name resolved to a field which holds a stacktrace. createhistfield() picks HISTFIELDFNSTACK on the strength of the field pointer alone, which reads a dataloc word from the record and follows its low 16 bits as an offset into the same record. eventhisttrigger() takes the first word there as an entry count and copies that many longs into a 31 entry array: nentries = stack; memcpy(entries, ++stack, nentries sizeof(unsigned long)); Neither end of that copy is bounded, and the count is whatever the event holds at the offset, so any field will do: # cd /sys/kernel/tracing/events/sched/schedprocessfork # echo 'hist:keys=parentpid.stacktrace' > trigger # (true) BUG: kernel NULL pointer dereference, address: 0000000000000008 RIP: 0010:rbinsertcolor+0x18/0x130 timerqueuelinkedadd+0x7e/0xd0 enqueuehrtimer+0x39/0xb0 hrtimerrunqueues+0x10f/0x1f0 </IRQ> RIP: 0010:memcpy+0xc/0x30 eventhisttrigger+0x165/0x690 The timer interrupt landed on the rbtree the copy had already run over. No debug options are needed for this; KASAN reports the same write as an out-of-bounds read of 13835058055416381440 bytes. Documentation/trace/histogram.rst already states the rule, "must be a long[] type", so enforce it once the name has been resolved. Names which resolve to no field at all, "hitcount.stacktrace" and the common pseudo-fields, are refused for the same reason: they hold no stacktrace to read.