> Subject: [PATCH v2 1/3] udmabuf: fix racy memfd sealing check
>
> The current check_memfd_seals() is racy: Since we first do
> check_memfd_seals() and then udmabuf_pin_folios() without holding any
> relevant lock across both, F_SEAL_WRITE can be set in between.
> This is problematic because we can end up holding pins to pages in a
> write-sealed memfd.
>
> Fix it using the inode lock, that's probably the easiest way.
> In the future, we might want to consider moving this logic into memfd,
> especially if anyone else wants to use memfd_pin_folios().
>
> Reported-by: Julian Orth <ju.o...@gmail.com>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219106
> Closes:
> https://lore.kernel.org/r/CAG48ez0w8HrFEZtJkfmkVKFDhE5aP7nz=obrimeTg
> pd+stk...@mail.gmail.com
> Fixes: fbb0de795078 ("Add udmabuf misc device")
> Cc: sta...@vger.kernel.org
> Signed-off-by: Jann Horn <ja...@google.com>
> ---
> drivers/dma-buf/udmabuf.c | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index
> 8ce1f074c2d32a0a9f59ff7184359e37d56548c6..c1d8c2766d6d36fc5fe1b3d73
> 057f6e01ec6678f 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -436,14 +436,19 @@ static long udmabuf_create(struct miscdevice
> *device,
> goto err;
> }
>
> + /*
> + * Take the inode lock to protect against concurrent
> + * memfd_add_seals(), which takes this lock in write mode.
> + */
Thank you for adding comments.
Acked-by: Vivek Kasireddy <vivek.kasire...@intel.com>
> + inode_lock_shared(file_inode(memfd));
> ret = check_memfd_seals(memfd);
> - if (ret < 0) {
> - fput(memfd);
> - goto err;
> - }
> + if (ret)
> + goto out_unlock;
>
> ret = udmabuf_pin_folios(ubuf, memfd, list[i].offset,
> list[i].size, folios);
> +out_unlock:
> + inode_unlock_shared(file_inode(memfd));
> fput(memfd);
> if (ret)
> goto err;
>
> --
> 2.47.0.338.g60cca15819-goog
