A crash was observed with the following output:

BUG: kernel NULL pointer dereference, address: 0000000000000010
Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 2 UID: 0 PID: 92 Comm: osnoise_cpus Not tainted 6.17.0-rc4-00201-gd69eb204c255 #138 PREEMPT(voluntary)
RIP: 0010:bitmap_parselist+0x53/0x3e0
Call Trace:
 <TASK>
 osnoise_cpus_write+0x7a/0x190
 vfs_write+0xf8/0x410
 ? do_sys_openat2+0x88/0xd0
 ksys_write+0x60/0xd0
 do_syscall_64+0xa4/0x260
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
 </TASK>

This issue can be reproduced by below code:

fd=open("/sys/kernel/debug/tracing/osnoise/cpus", O_WRONLY);
write(fd, "0-2", 0);

When user pass 'count=0' to osnoise_cpus_write(), kmalloc() will return
ZERO_SIZE_PTR (16) and cpulist_parse() treat it as a normal value, which
trigger the null pointer dereference. Add check for the parameter 'count'.

Link: https://lore.kernel.org/all/20250905032544.231962-1-wangliang74@huawei.com/
Fixes: 17f89102fe23 ("tracing/osnoise: Allow arbitrarily long CPU string")
Signed-off-by: Wang Liang <wangliang74@huawei.com>
---
v2: return 0 when sending a count of 0.
---
 kernel/trace/trace_osnoise.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index fd259da0aa64..337bc0eb5d71 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -2322,6 +2322,9 @@ osnoise_cpus_write(struct file *filp, const char __user *ubuf, size_t count,
 	int running, err;
 	char *buf __free(kfree) = NULL;
 
+	if (count < 1)
+		return 0;
+
 	buf = kmalloc(count, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
-- 
2.34.1

On Sat, 6 Sep 2025 11:56:10 +0800
Wang Liang <wangliang74@huawei.com> wrote:

> A crash was observed with the following output:
> 
> BUG: kernel NULL pointer dereference, address: 0000000000000010
> Oops: Oops: 0000 [#1] SMP NOPTI
> CPU: 2 UID: 0 PID: 92 Comm: osnoise_cpus Not tainted 6.17.0-rc4-00201-gd69eb204c255 #138 PREEMPT(voluntary)
> RIP: 0010:bitmap_parselist+0x53/0x3e0
> Call Trace:
>  <TASK>
>  osnoise_cpus_write+0x7a/0x190
>  vfs_write+0xf8/0x410
>  ? do_sys_openat2+0x88/0xd0
>  ksys_write+0x60/0xd0
>  do_syscall_64+0xa4/0x260
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>  </TASK>
> 
> This issue can be reproduced by below code:
> 
> fd=open("/sys/kernel/debug/tracing/osnoise/cpus", O_WRONLY);
> write(fd, "0-2", 0);
> 
> When user pass 'count=0' to osnoise_cpus_write(), kmalloc() will return
> ZERO_SIZE_PTR (16) and cpulist_parse() treat it as a normal value, which
> trigger the null pointer dereference. Add check for the parameter 'count'.
> 
> Link: https://lore.kernel.org/all/20250905032544.231962-1-wangliang74@huawei.com/
> Fixes: 17f89102fe23 ("tracing/osnoise: Allow arbitrarily long CPU string")
> Signed-off-by: Wang Liang <wangliang74@huawei.com>
> ---
> v2: return 0 when sending a count of 0.

FYI, I usually have this say:

Changes since v2: https://lore.kernel.org/all/20250905032544.231962-1-wangliang74@huawei.com/

and list the rest.

I know Linus doesn't like links to the patch, but I find them useful, and
even more useful when the patch has a link to previous versions. ;-)

I see that you did add it to the "link" above, which is probably fine too.

-- Steve

> ---
>  kernel/trace/trace_osnoise.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
> index fd259da0aa64..337bc0eb5d71 100644
> --- a/kernel/trace/trace_osnoise.c
> +++ b/kernel/trace/trace_osnoise.c
> @@ -2322,6 +2322,9 @@ osnoise_cpus_write(struct file *filp, const char
> __user *ubuf, size_t count, int running, err;
>  	char *buf __free(kfree) = NULL;
>  
> +	if (count < 1)
> +		return 0;
> +
>  	buf = kmalloc(count, GFP_KERNEL);
>  	if (!buf)
>  		return -ENOMEM;