Re: [PATCH] firmware: tegra: bpmp: refactor deprecated strncpy

[Kees Cook]

On Wed, Sep 13, 2023 at 07:38:44PM +, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We should prefer more robust and less ambiguous string interfaces.
> 
> It seems like the filename stored at `namevirt` is expected to be
> NUL-terminated.

This took me a bit to establish, but yes: buf[256] is used to store
filename, so it'll always be %NUL-terminated with the 256 bytes, which
is the same size used to allocate virtname, which means it will always
be %NUL-terminated.

> 
> A suitable replacement is `strscpy_pad` due to the fact that it
> guarantees NUL-termination on the destination buffer whilst maintaining
> the NUL-padding behavior that strncpy provides.
> 
> Link: 
> https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
>  [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-harden...@vger.kernel.org
> Signed-off-by: Justin Stitt 

This one looks weird because namevirt seems unused, but I assume there's
some kind of DMA side-effect happening somewhere?

But, yes, after digging around here, I think this all looks right.

Reviewed-by: Kees Cook 

-- 
Kees Cook

[PATCH] firmware: tegra: bpmp: refactor deprecated strncpy

[Justin Stitt]

`strncpy` is deprecated for use on NUL-terminated destination strings [1].

We should prefer more robust and less ambiguous string interfaces.

It seems like the filename stored at `namevirt` is expected to be
NUL-terminated.

A suitable replacement is `strscpy_pad` due to the fact that it
guarantees NUL-termination on the destination buffer whilst maintaining
the NUL-padding behavior that strncpy provides.

Link: 
https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
 [1]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-harden...@vger.kernel.org
Signed-off-by: Justin Stitt 
---
Note: compile tested only.
---
 drivers/firmware/tegra/bpmp-debugfs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/tegra/bpmp-debugfs.c 
b/drivers/firmware/tegra/bpmp-debugfs.c
index 6dfe3d34109e..bbcdd9fed3fb 100644
--- a/drivers/firmware/tegra/bpmp-debugfs.c
+++ b/drivers/firmware/tegra/bpmp-debugfs.c
@@ -610,7 +610,7 @@ static int debugfs_show(struct seq_file *m, void *p)
}
 
len = strlen(filename);
-   strncpy(namevirt, filename, namesize);
+   strscpy_pad(namevirt, filename, namesize);
 
err = mrq_debugfs_read(bpmp, namephys, len, dataphys, datasize,
   );
@@ -661,7 +661,7 @@ static ssize_t debugfs_store(struct file *file, const char 
__user *buf,
}
 
len = strlen(filename);
-   strncpy(namevirt, filename, namesize);
+   strscpy_pad(namevirt, filename, namesize);
 
if (copy_from_user(datavirt, buf, count)) {
err = -EFAULT;

---
base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
change-id: 20230913-strncpy-drivers-firmware-tegra-bpmp-debugfs-c-54f7baaf32c0

Best regards,
--
Justin Stitt