On Fri, Nov 3, 2023 at 3:38 AM Philipp Stanner wrote:
>
> ioctl.c utilizes memdup_user() to copy a userspace array. This is done
> without an overflow-check.
>
> Use the new wrapper memdup_array_user() to copy the array more safely.
>
> Suggested-by: Dave Airlie <airlied@xxxxxxxxxx>
> Signed-off-by: Philipp Stanner <pstanner@xxxxxxxxxx>
> ---
> Linus recently merged this new wrapper for Kernel v6.7
The following overflow check is performed just before the usage of
memdup_user():
if (nsegs > UINT_MAX / sizeof(__u64))
goto out;
This was introduced by commit 1ecd3c7ea76488 ("nilfs2: avoid
overflowing segment numbers in nilfs_ioctl_clean_segments()") to avoid
overflowing nsegs * sizeof(__u64) in the subsequent call to
memdup_user().
I learned about memdup_array_user() this time, and it seems to check
for overflow when multiplying two size_t arguments (i.e. the number of
elements and size of the array to be copied).
Since size_t is 32-bit or 64-bit depending on the architecture, I
think the overflow check that memdup_array_user() does
is included in the above upper limit check by UINT_MAX.
So, for security reasons, I don't think this change is necessary. (Am
I missing something?)
In terms of cleanup, I think the clarification this patch brings is
good, but in that case, I'm concerned about the duplication of
overflow checks.
Thanks,
Ryusuke Konishi
> ---
> fs/nilfs2/ioctl.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
> index 40ffade49f38..6a9dceebb18d 100644
> --- a/fs/nilfs2/ioctl.c
> +++ b/fs/nilfs2/ioctl.c
> @@ -877,11 +877,11 @@ static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
>
> /*
> * argv[4] points to segment numbers this ioctl cleans. We
> - * use kmalloc() for its buffer because memory used for the
> - * segment numbers is enough small.
> + * use kmalloc() for its buffer because the memory used for the
> + * segment numbers is small enough.
> */
> - kbufs[4] = memdup_user((void __user *)(unsigned long)argv[4].v_base,
> - nsegs * sizeof(__u64));
> + kbufs[4] = memdup_array_user((void __user *)(unsigned long)argv[4].v_base,
> + nsegs, sizeof(__u64));
> if (IS_ERR(kbufs[4])) {
> ret = PTR_ERR(kbufs[4]);
> goto out;
> --
> 2.41.0
>
