__string could get a dst string with length less than
TASK_COMM_LEN.

a task->comm possbile change dynamic that can cause
out of bounds access for the dst string buffer.

change it as arrary with same length TASK_COMM_LEN,
this aligns the same usage of include/trace on task->comm.

Signed-off-by: Kassey Li <quic_yingangl@quicinc.com>
---
 include/trace/events/cgroup.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/trace/events/cgroup.h b/include/trace/events/cgroup.h
index dd7d7c9efecd..d0c5f93e3611 100644
--- a/include/trace/events/cgroup.h
+++ b/include/trace/events/cgroup.h
@@ -130,7 +130,7 @@ DECLARE_EVENT_CLASS(cgroup_migrate,
 		__field(	u64,		dst_id			)
 		__field(	int,		pid			)
 		__string(	dst_path,	path			)
-		__string(	comm,		task->comm		)
+		__array(char,   comm, TASK_COMM_LEN)
 	),
 
 	TP_fast_assign(
@@ -139,12 +139,12 @@ DECLARE_EVENT_CLASS(cgroup_migrate,
 		__entry->dst_level = dst_cgrp->level;
 		__assign_str(dst_path, path);
 		__entry->pid = task->pid;
-		__assign_str(comm, task->comm);
+		memcpy(__entry->comm, task->comm, TASK_COMM_LEN);
 	),
 
 	TP_printk("dst_root=%d dst_id=%llu dst_level=%d dst_path=%s pid=%d comm=%s",
 		  __entry->dst_root, __entry->dst_id, __entry->dst_level,
-		  __get_str(dst_path), __entry->pid, __get_str(comm))
+		  __get_str(dst_path), __entry->pid, __entry->comm)
 );
 
 DEFINE_EVENT(cgroup_migrate, cgroup_attach_task,
-- 
2.17.1

hello:
    here is the instance of the problem：
    may you kindly review this change  ?

Unable to handle kernel write to read-only memory at virtual address 
ffffffbcf7450000

Call trace:
  dump_backtrace.cfi_jt+0x0/0x4
  show_stack+0x14/0x1c
  dump_stack+0xa0/0xd8
  die_callback+0x248/0x24c
  notify_die+0x7c/0xf8
  die+0xac/0x290
  die_kernel_fault+0x88/0x98
  die_kernel_fault+0x0/0x98
  do_page_fault+0xa0/0x544
  do_mem_abort+0x60/0x10c
  el1_da+0x1c/0xc4
  trace_event_raw_event_cgroup_migrate+0x124/0x170
  cgroup_attach_task+0x2e8/0x41c
  __cgroup1_procs_write+0x114/0x1ec
  cgroup1_tasks_write+0x10/0x18
  cgroup_file_write+0xa4/0x208
  kernfs_fop_write+0x1f0/0x2f4
  __vfs_write+0x5c/0x200
  vfs_write+0xe0/0x1a0
  ksys_write+0x74/0xdc
  __arm64_sys_write+0x18/0x20
  el0_svc_common+0xc0/0x1a4
  el0_svc_compat_handler+0x18/0x20
  el0_svc_compat+0x8/0x2c



On 9/20/2022 4:49 PM, Kassey Li wrote:
> __string could get a dst string with length less than
> TASK_COMM_LEN.
> 
> a task->comm possbile change dynamic that can cause
> out of bounds access for the dst string buffer.
> 
> change it as arrary with same length TASK_COMM_LEN,
> this aligns the same usage of include/trace on task->comm.
> 
> Signed-off-by: Kassey Li <quic_yingangl@quicinc.com>
> ---
>   include/trace/events/cgroup.h | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/include/trace/events/cgroup.h b/include/trace/events/cgroup.h
> index dd7d7c9efecd..d0c5f93e3611 100644
> --- a/include/trace/events/cgroup.h
> +++ b/include/trace/events/cgroup.h
> @@ -130,7 +130,7 @@ DECLARE_EVENT_CLASS(cgroup_migrate,
>   		__field(	u64,		dst_id			)
>   		__field(	int,		pid			)
>   		__string(	dst_path,	path			)
> -		__string(	comm,		task->comm		)
> +		__array(char,   comm, TASK_COMM_LEN)
>   	),
>   
>   	TP_fast_assign(
> @@ -139,12 +139,12 @@ DECLARE_EVENT_CLASS(cgroup_migrate,
>   		__entry->dst_level = dst_cgrp->level;
>   		__assign_str(dst_path, path);
>   		__entry->pid = task->pid;
> -		__assign_str(comm, task->comm);
> +		memcpy(__entry->comm, task->comm, TASK_COMM_LEN);
>   	),
>   
>   	TP_printk("dst_root=%d dst_id=%llu dst_level=%d dst_path=%s pid=%d comm=%s",
>   		  __entry->dst_root, __entry->dst_id, __entry->dst_level,
> -		  __get_str(dst_path), __entry->pid, __get_str(comm))
> +		  __get_str(dst_path), __entry->pid, __entry->comm)
>   );
>   
>   DEFINE_EVENT(cgroup_migrate, cgroup_attach_task,