alpha: fix broken network checksum

Mikulas Patocka · mattst88 · commit 0ef38d70d411 · 2014-01-31T09:21:55.000-08:00
The patch 3ddc5b4 breaks networking on alpha (there is a follow-up fix 5cfe8f1, but networking is still broken even with the second patch). The patch 3ddc5b4 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
@@ -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;
 }

Original file line number	Diff line number	Diff line change
`@@ -378,6 +378,11 @@ csum_partial_copy_from_user(const void __user src, void dst, int len,`
`378`	`378`	`__wsum`
`379`	`379`	`csum_partial_copy_nocheck(const void src, void dst, int len, __wsum sum)`
`380`	`380`	`{`
`381`		`- return csum_partial_copy_from_user((__force const void __user *)src,`
`382`		`- dst, len, sum, NULL);`
	`381`	`+ __wsum checksum;`
	`382`	`+ mm_segment_t oldfs = get_fs();`
	`383`	`+ set_fs(KERNEL_DS);`
	`384`	`+ checksum = csum_partial_copy_from_user((__force const void __user *)src,`
	`385`	`+ dst, len, sum, NULL);`
	`386`	`+ set_fs(oldfs);`
	`387`	`+ return checksum;`
`383`	`388`	`}`