strncpy is deprecated and as such we should prefer less ambiguous and
more robust string interfaces [1].
There's a lot of manual memory management to get a prefix and name into
a string. Let's use an easier to understand and more robust interface in
scnprintf() to accomplish the same task while enabling us to check for
possible truncation, resulting in a soft warning.
Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: [email protected]
Signed-off-by: Justin Stitt <[email protected]>
---
Split from https://lore.kernel.org/all/[email protected]/
with feedback from Christoph H.
---
fs/xfs/xfs_xattr.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/fs/xfs/xfs_xattr.c b/fs/xfs/xfs_xattr.c
index 364104e1b38a..bc7246eaebdd 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, name);
+
+ if (actual_len < combined_len)
+ xfs_warn(context->dp->i_mount,
+ "cannot completely copy %s%s to context buffer resulting in truncation",
+ prefix, name);
compute_size:
context->count += prefix_len + namelen + 1;
---
base-commit: c85af715cac0a951eea97393378e84bb49384734
change-id: 20240405-strncpy-xattr-split2-0a3aff0c6a20
Best regards,
--
Justin Stitt <[email protected]>
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 != ?
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.
How was this tested?
Hi,
On Tue, Apr 9, 2024 at 6:32 AM Christoph Hellwig <[email protected]> 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
On Tue, Apr 9, 2024 at 5:23 PM Justin Stitt <[email protected]> wrote:
>
> Hi,
>
> On Tue, Apr 9, 2024 at 6:32 AM Christoph Hellwig <[email protected]> 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;
> ---
I copy pasted from vim -> gmail and it completely ate all my tabs.
When I actually send the new patch, if needed, it will be formatted
correctly :)
>
>
>
> >
> > 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
On Tue, Apr 09, 2024 at 05:27:34PM -0700, Justin Stitt wrote:
> On Tue, Apr 9, 2024 at 5:23 PM Justin Stitt <[email protected]> wrote:
> >
> > Hi,
> >
> > On Tue, Apr 9, 2024 at 6:32 AM Christoph Hellwig <[email protected]> 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;
> > ---
>
> I copy pasted from vim -> gmail and it completely ate all my tabs.
> When I actually send the new patch, if needed, it will be formatted
> correctly :)
Yeah, the "%.*s" version looks better.
> >
> >
> >
> > >
> > > 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
Would you mind adding "-g attr,label" into the mix so that you're running all
the functional tests for xattr and fs label functionality?
--D
> >
> > Thanks
> > Justin
>