linux-kernel - RE: [PATCH 05/11] iov_iter: merge the compat case into rw_copy_check

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Message-ID: <7167a94511a84f30b18733d56007a7a5@AcuMS.aculab.com>
Date:   Fri, 8 Jan 2021 11:49:27 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Christoph Hellwig' <hch@....de>,
        Alexander Viro <viro@...iv.linux.org.uk>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>, Arnd Bergmann <arnd@...db.de>,
        David Howells <dhowells@...hat.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
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        "io-uring@...r.kernel.org" <io-uring@...r.kernel.org>,
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        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>
Subject: RE: [PATCH 05/11] iov_iter: merge the compat case into
 rw_copy_check_uvector

From: Christoph Hellwig <hch@....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@....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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