Re: [PATCH] fs/ntfs3: fix KMSAN uninit-value in ni_create_attr_list

[Nirbhay Sharma]

On 10/7/25 4:08 AM, Nirbhay Sharma wrote:
> The call to kmalloc() to allocate the attribute list buffer is given a
> size of al_aligned(rs). This size can be larger than the data
> subsequently copied into the buffer, leaving trailing bytes uninitialized.
>
> This can trigger a KMSAN "uninit-value" warning if that memory is
> later accessed.
>
> Fix this by using kzalloc() instead, which ensures the entire
> allocated buffer is zero-initialized, preventing the warning.
>
> Reported-by: syzbot+83c9dd5c0dcf6184fdbf@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=83c9dd5c0dcf6184fdbf
> Signed-off-by: Nirbhay Sharma <nirbhay.lkd@xxxxxxxxx>
> ---
> The following syzbot test commands were used to verify the fix against
> both linux-next and a specific mainline commit. Both kernels were
> configured with CONFIG_KMSAN=y, and no KMSAN warnings were observed
> with the patch applied.
>
> An attempt to test against the latest mainline tip failed due to an
> unrelated boot failure in the SCSI subsystem (KMSAN: use-after-free in
> scsi_get_vpd_buf). Therefore, testing was done on the last known-good
> mainline commit below.
>
> For mainline commit 9b0d551bcc05 ("Merge tag 'pull-misc' of..."):
> #syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 9b0d551bcc05
>
> For the linux-next branch:
> #syz test: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
>
>   fs/ntfs3/frecord.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/ntfs3/frecord.c b/fs/ntfs3/frecord.c
> index 8f9fe1d7a690..4fe8da7fc034 100644
> --- a/fs/ntfs3/frecord.c
> +++ b/fs/ntfs3/frecord.c
> @@ -767,7 +767,7 @@ int ni_create_attr_list(struct ntfs_inode *ni)
>   	 * Skip estimating exact memory requirement.
>   	 * Looks like one record_size is always enough.
>   	 */
> -	le = kmalloc(al_aligned(rs), GFP_NOFS);
> +	le = kzalloc(al_aligned(rs), GFP_NOFS);
>   	if (!le)
>   		return -ENOMEM;
>   
Hi Konstantin,

I sent this patch about 3 weeks ago and haven't heard back yet. I wanted
to check if there are any concerns with the patch or if any changes are
needed. The fix addresses a KMSAN uninit-value bug and has been tested
successfully on both linux-next and the commit from the syzbot report.

Please let me know if you need any additional information or testing.

Thanks,
Nirbhay