Re: [PATCH v6 12/12] kernel/kthread: show a warning if kthread's comm is truncated
From: Kees Cook <hidden>
Date: 2021-10-25 21:36:03
Also in:
bpf, linux-fsdevel, linux-mm, linux-rdma, lkml, netdev
On Mon, Oct 25, 2021 at 08:33:15AM +0000, Yafang Shao wrote:
quoted hunk ↗ jump to hunk
Show a warning if task comm is truncated. Below is the result of my test case: truncated kthread comm:I-am-a-kthread-with-lon, pid:14 by 6 characters Suggested-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Yafang Shao <redacted> Reviewed-by: Kees Cook <redacted> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Arnaldo Carvalho de Melo <redacted> Cc: Andrii Nakryiko <redacted> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Kees Cook <redacted> Cc: Petr Mladek <pmladek@suse.com> --- kernel/kthread.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)diff --git a/kernel/kthread.c b/kernel/kthread.c index 5b37a8567168..46b924c92078 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c@@ -399,12 +399,17 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data), if (!IS_ERR(task)) { static const struct sched_param param = { .sched_priority = 0 }; char name[TASK_COMM_LEN]; + int len; /* * task is already visible to other tasks, so updating * COMM must be protected. */ - vsnprintf(name, sizeof(name), namefmt, args); + len = vsnprintf(name, sizeof(name), namefmt, args); + if (len >= TASK_COMM_LEN) {
And since this failure case is slow-path, we could improve the warning
as other had kind of suggested earlier with something like this instead:
char *full_comm;
full_comm = kvasprintf(GFP_KERNEL, namefmt, args);
pr_warn("truncated kthread comm '%s' to '%s' (pid:%d)\n",
full_comm, name);
kfree(full_comm);
}set_task_comm(task, name); /* * root may have changed our (kthreadd's) priority or CPU mask. -- 2.17.1
-- Kees Cook