On Tue, May 5, 2020 at 9:07 PM Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
>
> The "buflen" value comes from the user and there is a potential that it
> could be zero. In do_handle_to_path() we know that "handle->handle_bytes"
> is non-zero and we do:
>
> handle_dwords = handle->handle_bytes >> 2;
>
> So values 1-3 become zero. Then in ovl_fh_to_dentry() we do:
>
> int len = fh_len << 2;
>
> So now len is in the "0,4-128" range and a multiple of 4. But if
> "buflen" is zero it will try to copy negative bytes when we do the
> memcpy in ovl_fid_to_fh().
>
> memcpy(&fh->fb, fid, buflen - OVL_FH_WIRE_OFFSET);
>
> And that will lead to a crash. Thanks to Amir Goldstein for his help
> with this patch.
>
> Fixes: cbe7fba8edfc: ("ovl: make sure that real fid is 32bit aligned in memory")
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> ---
> fs/overlayfs/export.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
> index 475c61f53f0fe..0e58213ace6d7 100644
> --- a/fs/overlayfs/export.c
> +++ b/fs/overlayfs/export.c
> @@ -776,6 +776,9 @@ static struct ovl_fh *ovl_fid_to_fh(struct fid *fid, int buflen, int fh_type)
> {
> struct ovl_fh *fh;
>
> + if (buflen <= OVL_FH_WIRE_OFFSET)
> + return ERR_PTR(-EINVAL);
> +
Sorry, I should have been more specific.
This check belongs after fh_type != OVL_FILEID_V0
because it is only relevant for OVL_FILEID_V0.
For OVL_FILEID_V1 len properly checked by ovl_check_fh_len().
Otherwise feel free to add:
Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
Thanks,
Amir.
