CVE-2024-26703: tracing/timerlat: Move hrtimer_init to timerlat_fd open()

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

tracing/timerlat: Move hrtimerinit to timerlatfd open()

Currently, the timerlat's hrtimer is initialized at the first read of timerlatfd, and destroyed at close(). It works, but it causes an error if the user program open() and close() the file without reading.

Here's an example:

# echo NOOSNOISEWORKLOAD > /sys/kernel/debug/tracing/osnoise/options # echo timerlat > /sys/kernel/debug/tracing/currenttracer

# cat <<EOF > ./timerlatload.py # !/usr/bin/env python3

timerlatfd = open("/sys/kernel/tracing/osnoise/percpu/cpu0/timerlatfd", 'r') timerlatfd.close(); EOF

# ./taskset -c 0 ./timerlatload.py <BOOM>

BUG: kernel NULL pointer dereference, address: 0000000000000010 #PF: supervisor read access in kernel mode #PF: errorcode(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP NOPTI CPU: 1 PID: 2673 Comm: python3 Not tainted 6.6.13-200.fc39.x8664 #1 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-1.fc39 04/01/2014 RIP: 0010:hrtimeractive+0xd/0x50 Code: 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 48 8b 57 30 <8b> 42 10 a8 01 74 09 f3 90 8b 42 10 a8 01 75 f7 80 7f 38 00 75 1d RSP: 0018:ffffb031009b7e10 EFLAGS: 00010286 RAX: 000000000002db00 RBX: ffff9118f786db08 RCX: 0000000000000000 RDX: 0000000000000000 RSI: ffff9117a0e64400 RDI: ffff9118f786db08 RBP: ffff9118f786db80 R08: ffff9117a0ddd420 R09: ffff9117804d4f70 R10: 0000000000000000 R11: 0000000000000000 R12: ffff9118f786db08 R13: ffff91178fdd5e20 R14: ffff9117840978c0 R15: 0000000000000000 FS: 00007f2ffbab1740(0000) GS:ffff9118f7840000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000010 CR3: 00000001b402e000 CR4: 0000000000750ee0 PKRU: 55555554 Call Trace: <TASK> ? die+0x23/0x70 ? pagefaultoops+0x171/0x4e0 ? srsoaliasreturnthunk+0x5/0x7f ? avchasextendedperms+0x237/0x520 ? excpagefault+0x7f/0x180 ? asmexcpagefault+0x26/0x30 ? hrtimeractive+0xd/0x50 hrtimercancel+0x15/0x40 timerlatfdrelease+0x48/0xe0 fput+0xf5/0x290 x64sysclose+0x3d/0x80 dosyscall64+0x60/0x90 ? srsoaliasreturnthunk+0x5/0x7f ? x64sysioctl+0x72/0xd0 ? srsoaliasreturnthunk+0x5/0x7f ? syscallexittousermode+0x2b/0x40 ? srsoaliasreturnthunk+0x5/0x7f ? dosyscall64+0x6c/0x90 ? srsoaliasreturnthunk+0x5/0x7f ? exittousermodeprepare+0x142/0x1f0 ? srsoaliasreturnthunk+0x5/0x7f ? syscallexittousermode+0x2b/0x40 ? srsoaliasreturnthunk+0x5/0x7f ? dosyscall64+0x6c/0x90 entrySYSCALL64afterhwframe+0x6e/0xd8 RIP: 0033:0x7f2ffb321594 Code: 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 80 3d d5 cd 0d 00 00 74 13 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 3c c3 0f 1f 00 55 48 89 e5 48 83 ec 10 89 7d RSP: 002b:00007ffe8d8eef18 EFLAGS: 00000202 ORIGRAX: 0000000000000003 RAX: ffffffffffffffda RBX: 00007f2ffba4e668 RCX: 00007f2ffb321594 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003 RBP: 00007ffe8d8eef40 R08: 0000000000000000 R09: 0000000000000000 R10: 55c926e3167eae79 R11: 0000000000000202 R12: 0000000000000003 R13: 00007ffe8d8ef030 R14: 0000000000000000 R15: 00007f2ffba4e668 </TASK> CR2: 0000000000000010 ---[ end trace 0000000000000000 ]---

Move hrtimerinit to timerlatfd open() to avoid this problem.