Re: [PATCH] tracing: Resolve stack corruption due to string copy

From: Steven Rostedt
Date: Wed May 03 2017 - 10:00:42 EST

On Wed, 3 May 2017 15:41:14 +0530
Amit Pundir <amit.pundir@xxxxxxxxxx> wrote:

> From: Amey Telawane <ameyt@xxxxxxxxxxxxxx>
> Strcpy has no limit on string being copied which causes
> stack corruption leading to kernel panic. Use strlcpy to
> resolve the issue by providing length of string to be copied.
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Amey Telawane <ameyt@xxxxxxxxxxxxxx>
> [AmitP: Cherry-picked this commit from CodeAurora kernel/msm-3.10
> Signed-off-by: Amit Pundir <amit.pundir@xxxxxxxxxx>
> ---
> This patch featured in Android Security Bulletin for May 2017,
> but it is not upstreamed yet and I couldn't find any previous
> upstream submission as well.
> kernel/trace/trace.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index bd8fb5cfda4d..b227e141e1f1 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -1976,7 +1976,7 @@ static void __trace_find_cmdline(int pid, char comm[])
> map = savedcmd->map_pid_to_cmdline[pid];
> if (map != NO_CMDLINE_MAP)
> - strcpy(comm, get_saved_cmdlines(map));
> + strlcpy(comm, get_saved_cmdlines(map), TASK_COMM_LEN - 1);

Actually it should be TASK_COMM_LEN (without the -1), as all comms
passed in must be of that length. The strlcpy will add '\0' to the
len-1 passed in. Passing in TASK_COMM_LEN-1 will yield a '\0' at

Note, I don't see anyway to trigger a bug. To me this looks simply like
someone saw "strcpy" and said to themselves "oh this is a bug", when
actuality it is not. I don't mind the extra security added, but I don't
think this even needs to go to stable. The reason is that the comm used
within the kernel is always created by the kernel, and always has a
terminating nul character. There's other places in the kernel that will
bug if that is not true.

The comm is set by __set_task_comm() which uses strlcpy().

I'll take this patch, but I'm going to strip the stable tag from it.

-- Steve

> else
> strcpy(comm, "<...>");
> }