bpf: Replace strncpy() with strscpy()

Using strncpy() on NUL-terminated strings is considered deprecated[1].
Moreover, if the length of 'task->comm' is less than the destination buffer
size, strncpy() will NUL-pad the destination buffer, which is a needless
performance penalty.

Replacing strncpy() with strscpy() fixes all these issues.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings

Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20220304070408.233658-1-ytcoode@gmail.com

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index ae64110..315053e 100644 (file)
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -225,13 +225,8 @@ BPF_CALL_2(bpf_get_current_comm, char *, buf, u32, size)
        if (unlikely(!task))
                goto err_clear;
 
-       strncpy(buf, task->comm, size);
-
-       /* Verifier guarantees that size > 0. For task->comm exceeding
-        * size, guarantee that buf is %NUL-terminated. Unconditionally
-        * done here to save the size test.
-        */
-       buf[size - 1] = 0;
+       /* Verifier guarantees that size > 0 */
+       strscpy(buf, task->comm, size);
        return 0;
 err_clear:
        memset(buf, 0, size);