[PATCH] dma-buf: Replace strlcpy() with strscpy()

[PATCH] dma-buf: Replace strlcpy() with strscpy()

[Kees Cook]

strlcpy() reads the entire source buffer first. This read may exceed
the destination size limit. This is both inefficient and can lead
to linear read overflows if a source string is not NUL-terminated[1].
Additionally, it returns the size of the source string, not the
resulting size of the destination string. In an effort to remove strlcpy()
completely[2], replace strlcpy() here with strscpy().

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy [1]
Link: https://github.com/KSPP/linux/issues/89 [2]
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Azeem Shaikh <azeemshaikh38@gmail.com>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/dma-buf/dma-buf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 21916bba77d5..8fe5aa67b167 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -46,12 +46,12 @@ static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen)
 {
 	struct dma_buf *dmabuf;
 	char name[DMA_BUF_NAME_LEN];
-	size_t ret = 0;
+	ssize_t ret = 0;
 
 	dmabuf = dentry->d_fsdata;
 	spin_lock(&dmabuf->name_lock);
 	if (dmabuf->name)
-		ret = strlcpy(name, dmabuf->name, DMA_BUF_NAME_LEN);
+		ret = strscpy(name, dmabuf->name, sizeof(name));
 	spin_unlock(&dmabuf->name_lock);
 
 	return dynamic_dname(buffer, buflen, "/%s:%s",
-- 
2.34.1

Re: [PATCH] dma-buf: Replace strlcpy() with strscpy()

[T.J. Mercier]

On Thu, Nov 16, 2023 at 11:14 AM Kees Cook <keescook@chromium.org> wrote:
>
> strlcpy() reads the entire source buffer first. This read may exceed
> the destination size limit. This is both inefficient and can lead
> to linear read overflows if a source string is not NUL-terminated[1].
> Additionally, it returns the size of the source string, not the
> resulting size of the destination string. In an effort to remove strlcpy()
> completely[2], replace strlcpy() here with strscpy().
>
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy [1]
> Link: https://github.com/KSPP/linux/issues/89 [2]
> Cc: Sumit Semwal <sumit.semwal@linaro.org>
> Cc: "Christian König" <christian.koenig@amd.com>
> Cc: Azeem Shaikh <azeemshaikh38@gmail.com>
> Cc: linux-media@vger.kernel.org
> Cc: dri-devel@lists.freedesktop.org
> Cc: linaro-mm-sig@lists.linaro.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: T.J. Mercier <tjmercier@google.com>

strscpy returns -E2BIG when it truncates / force null-terminates which
would provide the wrong argument for dynamic_dname, but
dma_buf_set_name{_user} makes sure we have a null-terminated string of
the appropriate maximum size in dmabuf->name.

Re: [PATCH] dma-buf: Replace strlcpy() with strscpy()

[Christian König]

Am 17.11.23 um 19:50 schrieb T.J. Mercier:
> On Thu, Nov 16, 2023 at 11:14 AM Kees Cook <keescook@chromium.org> wrote:
>> strlcpy() reads the entire source buffer first. This read may exceed
>> the destination size limit. This is both inefficient and can lead
>> to linear read overflows if a source string is not NUL-terminated[1].
>> Additionally, it returns the size of the source string, not the
>> resulting size of the destination string. In an effort to remove strlcpy()
>> completely[2], replace strlcpy() here with strscpy().
>>
>> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy [1]
>> Link: https://github.com/KSPP/linux/issues/89 [2]
>> Cc: Sumit Semwal <sumit.semwal@linaro.org>
>> Cc: "Christian König" <christian.koenig@amd.com>
>> Cc: Azeem Shaikh <azeemshaikh38@gmail.com>
>> Cc: linux-media@vger.kernel.org
>> Cc: dri-devel@lists.freedesktop.org
>> Cc: linaro-mm-sig@lists.linaro.org
>> Signed-off-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: T.J. Mercier <tjmercier@google.com>
>
> strscpy returns -E2BIG when it truncates / force null-terminates which
> would provide the wrong argument for dynamic_dname, but
> dma_buf_set_name{_user} makes sure we have a null-terminated string of
> the appropriate maximum size in dmabuf->name.

Thanks for that background check, I was about to note that this might 
not be a good idea.

Linus pretty clearly stated that he doesn't want to see patches like 
that one here, see this article as well. https://lwn.net/Articles/659214/

I think the commit message gives enough reason to merge the patch, so 
I'm going to push it to drm-misc-next. But please make sure to triple 
check stuff like this before sending.

Thanks,
Christian.