On Wed, Nov 10, 2021 at 09:28:12AM +0100, David Hildenbrand wrote:

On 08.11.21 09:38, Yafang Shao wrote:

quoted

Make sure the string set to task comm is always nul terminated.

strlcpy: "the result is always a valid NUL-terminated string that fits
in the buffer"

The only difference seems to be that strscpy_pad() pads the remainder
with zeroes.

Is this description correct and I am missing something important?

Yes, this makes sure it's zero padded just to be robust against full
tsk->comm copies that got noticed in other places.

The only other change is that we want to remove strlcpy() from the
kernel generally since it can trigger out-of-bound reads on the source
string[1].

So, in this case, the most robust version is to use strscpy_pad().

-Kees

[1] https://github.com/KSPP/linux/issues/89

quoted

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: Alexei Starovoitov <redacted>
Cc: Andrii Nakryiko <redacted>
Cc: Michal Miroslaw <mirq-linux@rere.qmqm.pl> 
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: David Hildenbrand <redacted>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <redacted>
Cc: Petr Mladek <pmladek@suse.com>
---
 fs/exec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/exec.c b/fs/exec.c
index a098c133d8d7..404156b5b314 100644
--- a/fs/exec.c
+++ b/fs/exec.c

@@ -1224,7 +1224,7 @@ void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
 {
 	task_lock(tsk);
 	trace_task_rename(tsk, buf);
-	strlcpy(tsk->comm, buf, sizeof(tsk->comm));
+	strscpy_pad(tsk->comm, buf, sizeof(tsk->comm));
 	task_unlock(tsk);
 	perf_event_comm(tsk, exec);
 }

-- 
Thanks,

David / dhildenb

-- 
Kees Cook