tracing/osnoise: Fix slab-out-of-bounds in _parse_integer_limit()

When config osnoise cpus by write() syscall, the following KASAN splat may
be observed:

BUG: KASAN: slab-out-of-bounds in _parse_integer_limit+0x103/0x130
Read of size 1 at addr ffff88810121e3a1 by task test/447
CPU: 1 UID: 0 PID: 447 Comm: test Not tainted 6.17.0-rc6-dirty #288 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x55/0x70
 print_report+0xcb/0x610
 kasan_report+0xb8/0xf0
 _parse_integer_limit+0x103/0x130
 bitmap_parselist+0x16d/0x6f0
 osnoise_cpus_write+0x116/0x2d0
 vfs_write+0x21e/0xcc0
 ksys_write+0xee/0x1c0
 do_syscall_64+0xa8/0x2a0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
 </TASK>

This issue can be reproduced by below code:

const char *cpulist = "1";
int fd=open("/sys/kernel/debug/tracing/osnoise/cpus", O_WRONLY);
write(fd, cpulist, strlen(cpulist));

Function bitmap_parselist() was called to parse cpulist, it require that
the parameter 'buf' must be terminated with a '\0' or '\n'. Fix this issue
by adding a '\0' to 'buf' in osnoise_cpus_write().

Cc: <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Link: https://lore.kernel.org/[email protected]
Fixes: 17f8910 ("tracing/osnoise: Allow arbitrarily long CPU string")
Signed-off-by: Wang Liang <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

Author: Wang Liang

kernel/trace/trace_osnoise.c

@@ -2325,12 +2325,13 @@ osnoise_cpus_write(struct file *filp, const char __user *ubuf, size_t count,
 	if (count < 1)
 		return 0;
 
-	buf = kmalloc(count, GFP_KERNEL);
+	buf = kmalloc(count + 1, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
 
 	if (copy_from_user(buf, ubuf, count))
 		return -EFAULT;
+	buf[count] = '\0';
 
 	if (!zalloc_cpumask_var(&osnoise_cpumask_new, GFP_KERNEL))
 		return -ENOMEM;