----- Original Message -----
> From: "Mikulas Patocka" <mpatocka@xxxxxxxxxx>
> To: "Mathieu Desnoyers" <mathieu.desnoyers@xxxxxxxxxxxx>, "Richard Henderson" <rth@xxxxxxxxxxx>, "Ivan Kokshaysky"
> <ink@xxxxxxxxxxxxxxxxxxxx>, "Matt Turner" <mattst88@xxxxxxxxx>, linux-alpha@xxxxxxxxxxxxxxx
> Cc: "David Miller" <davem@xxxxxxxxxxxxx>, "Oleg Nesterov" <oleg@xxxxxxxxxx>, "Jay Estabrook"
> <jay.estabrook@xxxxxxxxx>, "Michael Cree" <mcree@xxxxxxxxxxxx>, "Jens Axboe" <axboe@xxxxxxxxx>
> Sent: Wednesday, January 22, 2014 11:04:33 PM
> Subject: [PATCH] alpha: fix broken network checksum
>
> The patch 3ddc5b46a8e90f3c9251338b60191d0a804b0d92 breaks networking on
> alpha (there is a follow-up fix 5cfe8f1ba5eebe6f4b6e5858cdb1a5be4f3272a6,
> but networking is still broken even with the second patch).
>
> The patch 3ddc5b46a8e90f3c9251338b60191d0a804b0d92 makes
> csum_partial_copy_from_user check the pointer with access_ok. However,
> csum_partial_copy_from_user is called also from csum_partial_copy_nocheck
> and csum_partial_copy_nocheck is called on kernel pointers and it is
> supposed not to check pointer validity.
>
> This bug results in ssh session hangs if the system is loaded and bulk
> data are printed to ssh terminal.
>
> This patch fixes csum_partial_copy_nocheck to call set_fs(KERNEL_DS), so
> that access_ok in csum_partial_copy_from_user accepts kernel-space
> addresses.
I see that most architectures implement a csum_partial_copy_generic()
called from csum_partial_copy_nocheck() for this purpose rather than
re-using csum_partial_copy_from_user().
I understand that this fix is the minimal change needed to get things to
work, so I think it's important to pull it in, but it might be a good
thing to consider implementing a csum_partial_copy_generic() for alpha
eventually if performance matters.
Thanks!
Mathieu
>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
>
> ---
> arch/alpha/lib/csum_partial_copy.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> Index: linux-2.6-alpha/arch/alpha/lib/csum_partial_copy.c
> ===================================================================
> --- linux-2.6-alpha.orig/arch/alpha/lib/csum_partial_copy.c 2014-01-23
> 04:44:34.000000000 +0100
> +++ linux-2.6-alpha/arch/alpha/lib/csum_partial_copy.c 2014-01-23
> 04:45:43.000000000 +0100
> @@ -378,6 +378,11 @@ csum_partial_copy_from_user(const void _
> __wsum
> csum_partial_copy_nocheck(const void *src, void *dst, int len, __wsum sum)
> {
> - return csum_partial_copy_from_user((__force const void __user *)src,
> - dst, len, sum, NULL);
> + __wsum checksum;
> + mm_segment_t oldfs = get_fs();
> + set_fs(KERNEL_DS);
> + checksum = csum_partial_copy_from_user((__force const void __user *)src,
> + dst, len, sum, NULL);
> + set_fs(oldfs);
> + return checksum;
> }
>
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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