On Fri, Aug 27, 2021 at 10:52 PM Kees Cook [off-list ref] wrote:

On Sat, Aug 28, 2021 at 02:47:03AM +0100, Matthew Wilcox wrote:

quoted

On Fri, Aug 27, 2021 at 12:18:57PM -0700, Suren Baghdasaryan wrote:

quoted

+           anon_name = vma_anon_name(vma);
+           if (anon_name) {
+                   seq_pad(m, ' ');
+                   seq_puts(m, "[anon:");
+                   seq_write(m, anon_name, strlen(anon_name));
+                   seq_putc(m, ']');
+           }

Maybe after seq_pad, use: seq_printf(m, "[anon:%s]", anon_name);

Good idea. Will change.

quoted

...

quoted

+   case PR_SET_VMA_ANON_NAME:
+           name = strndup_user((const char __user *)arg,
+                               ANON_VMA_NAME_MAX_LEN);
+
+           if (IS_ERR(name))
+                   return PTR_ERR(name);
+
+           for (pch = name; *pch != '\0'; pch++) {
+                   if (!isprint(*pch)) {
+                           kfree(name);
+                           return -EINVAL;

I think isprint() is too weak a check.  For example, I would suggest
forbidding the following characters: ':', ']', '[', ' '.  Perhaps
isalnum() would be better?  (permit a-zA-Z0-9)  I wouldn't necessarily
be opposed to some punctuation characters, but let's avoid creating
confusion.  Do you happen to know which characters are actually in use
today?

There's some sense in refusing [, ], and :, but removing " " seems
unhelpful for reasonable descriptors. As long as weird stuff is escaped,
I think it's fine. Any parser can just extract with m|\[anon:(.*)\]$|

I see no issue in forbidding '[' and ']' but whitespace and ':' are
currently used by Android. Would forbidding or escaping '[' and ']' be
enough?

For example, just escape it here instead of refusing to take it. Something
like:

        name = strndup_user((const char __user *)arg,
                            ANON_VMA_NAME_MAX_LEN);
        escaped = kasprintf(GFP_KERNEL, "%pE", name);

Did you mean "%*pE" as in
https://www.kernel.org/doc/html/latest/core-api/printk-formats.html#raw-buffer-as-an-escaped-string
?

        if (escaped) {
                kfree(name);
                return -ENOMEM;
        }
        kfree(name);
        name = escaped;

--
Kees Cook