alpha: fix broken network checksum

The patch 2457d966ca51d61c57daaa310b83c049b586685c breaks networking on
alpha (there is a follow-up fix 5d1701cfe208409d51234408a06b4aaf46c2259f,
but networking is still broken even with the second patch).

The patch 2457d966ca51d61c57daaa310b83c049b586685c 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.

Cc: stable@vger.kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Matt Turner <mattst88@gmail.com>

diff --git a/arch/alpha/lib/csum_partial_copy.c b/arch/alpha/lib/csum_partial_copy.c
index ff3c10721caf67be1873f5c5b88623fc65fd89ea..5675dca8dbb1412e0b2fcea1c748ec9d757a3e8c 100644 (file)
--- a/arch/alpha/lib/csum_partial_copy.c
+++ b/arch/alpha/lib/csum_partial_copy.c
@@ -378,6 +378,11 @@ csum_partial_copy_from_user(const void __user *src, void *dst, int len,
 __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;
 }