CVE-2025-39683

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

tracing: Limit access to parser->buffer when tracegetuser failed

When the length of the string written to setftracefilter exceeds FTRACEBUFFMAX, the following KASAN alarm will be triggered:

BUG: KASAN: slab-out-of-bounds in strsep+0x18c/0x1b0 Read of size 1 at addr ffff0000d00bd5ba by task ash/165

CPU: 1 UID: 0 PID: 165 Comm: ash Not tainted 6.16.0-g6bcdbd62bd56-dirty Hardware name: linux,dummy-virt (DT) Call trace: showstack+0x34/0x50 (C) dumpstacklvl+0xa0/0x158 printaddressdescription.constprop.0+0x88/0x398 printreport+0xb0/0x280 kasan_report+0xa4/0xf0 __asanreportload1noabort+0x20/0x30 strsep+0x18c/0x1b0 ftraceprocessregex.isra.0+0x100/0x2d8 ftraceregex_release+0x484/0x618 __fput+0x364/0xa58 ____fput+0x28/0x40 taskworkrun+0x154/0x278 donotifyresume+0x1f0/0x220 el0svc+0xec/0xf0 el0t64synchandler+0xa0/0xe8 el0t64sync+0x1ac/0x1b0

The reason is that tracegetuser will fail when processing a string longer than FTRACEBUFFMAX, but not set the end of parser->buffer to 0. Then an OOB access will be triggered in ftraceregexrelease-> ftraceprocessregex->strsep->strpbrk. We can solve this problem by limiting access to parser->buffer when tracegetuser failed.