Hi,
On Tue, Apr 9, 2024 at 6:32 AM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>
> On Fri, Apr 05, 2024 at 07:45:08PM +0000, Justin Stitt wrote:
> > - memcpy(offset, prefix, prefix_len);
> > - offset += prefix_len;
> > - strncpy(offset, (char *)name, namelen); /* real name */
> > - offset += namelen;
> > - *offset = '\0';
> > +
> > + combined_len = prefix_len + namelen;
> > +
> > + /* plus one byte for \0 */
> > + actual_len = scnprintf(offset, combined_len + 1, "%s%s", prefix, name);
> > +
> > + if (actual_len < combined_len)
>
> Shouldn't this be a != ?
I guess it could be. It's a truncation check so I figured just
checking if the amount of bytes actually copied was less than the
total would suffice.
>
> That being said I think this is actually wrong - the attr names are
> not NULL-terminated on disk, which is why we have the explicit
> zero terminataion above.
Gotcha, in which case we could use the "%.*s" format specifier which
allows for a length argument. Does something like this look better?
diff --git a/fs/xfs/xfs_xattr.c b/fs/xfs/xfs_xattr.c
index 364104e1b38a..1b7e886e0f29 100644
--- a/fs/xfs/xfs_xattr.c
+++ b/fs/xfs/xfs_xattr.c
@@ -206,6 +206,7 @@ __xfs_xattr_put_listent(
{
char *offset;
int arraytop;
+ size_t combined_len, actual_len;
if (context->count < 0 || context->seen_enough)
return;
@@ -220,11 +221,16 @@ __xfs_xattr_put_listent(
return;
}
offset = context->buffer + context->count;
- memcpy(offset, prefix, prefix_len);
- offset += prefix_len;
- strncpy(offset, (char *)name, namelen); /* real name */
- offset += namelen;
- *offset = '\0';
+
+ combined_len = prefix_len + namelen;
+
+ /* plus one byte for \0 */
+ actual_len = scnprintf(offset, combined_len + 1, "%.*s%.*s",
+ prefix_len, prefix, namelen, name);
+
+ if (actual_len < combined_len)
+ xfs_warn(context->dp->i_mount,
+ "cannot completely copy context buffer resulting in truncation");
compute_size:
context->count += prefix_len + namelen + 1;
---
>
> How was this tested?
With https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git/about/
but using scripts + image from: https://github.com/tytso/xfstests-bld
here's the output log: https://pastebin.com/V2gFhbNZ wherein I ran the
5 default ones (I think?):
| Ran: generic/475 generic/476 generic/521 generic/522 generic/642
| Passed all 5 tests
Thanks
Justin
