RE: [PATCH 05/11] iov_iter: merge the compat case into rw_copy_check_uvector

David Laight
2021-01-08T11:51:40Z

From: Christoph Hellwig <hch@lst.de>
> Sent: 21 September 2020 15:34
>
> Stop duplicating the iovec verify code, and instead add add a
> __import_iovec helper that does the whole verify and import, but takes
> a bool compat to decided on the native or compat layout. This also
> ends up massively simplifying the calling conventions.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> lib/iov_iter.c | 195 ++++++++++++++++++-------------------------------
> 1 file changed, 70 insertions(+), 125 deletions(-)
>
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index a64867501a7483..8bfa47b63d39aa 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -10,6 +10,7 @@
> #include <net/checksum.h>
> #include <linux/scatterlist.h>
> #include <linux/instrumented.h>
> +#include <linux/compat.h>
>
> #define PIPE_PARANOIA /* for now */
>
> @@ -1650,43 +1651,76 @@ const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags)
> }
> EXPORT_SYMBOL(dup_iter);
>
> -static ssize_t rw_copy_check_uvector(int type,
> - const struct iovec __user *uvector, unsigned long nr_segs,
> - unsigned long fast_segs, struct iovec *fast_pointer,
> - struct iovec **ret_pointer)
> +static int compat_copy_iovecs_from_user(struct iovec *iov,
> + const struct iovec __user *uvector, unsigned long nr_segs)
> +{
> + const struct compat_iovec __user *uiov =
> + (const struct compat_iovec __user *)uvector;
> + unsigned long i;
> + int ret = -EFAULT;
> +
> + if (!user_access_begin(uvector, nr_segs * sizeof(*uvector)))
> + return -EFAULT;

I little bit late, but the above isn't quite right.
It should be sizeof(*iouv) - the length is double what it should be.

Not that access_ok() can fail for compat addresses
and the extra length won't matter for architectures that
need the address/length to open an address hole into userspace.

David

-
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