metag/usercopy: Fix alignment error checking

Fix the error checking of the alignment adjustment code in
raw_copy_from_user(), which mistakenly considers it safe to skip the
error check when aligning the source buffer on a 2 or 4 byte boundary.

If the destination buffer was unaligned it may have started to copy
using byte or word accesses, which could well be at the start of a new
(valid) source page. This would result in it appearing to have copied 1
or 2 bytes at the end of the first (invalid) page rather than none at
all.

Fixes: 373cd784d0fc ("metag: Memory handling")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-metag@vger.kernel.org
Cc: stable@vger.kernel.org

1 files changed, 4 insertions, 6 deletions

diff --git a/arch/metag/lib/usercopy.c b/arch/metag/lib/usercopy.c
index b4eb1f17069f..a6ced9691ddb 100644
--- a/arch/metag/lib/usercopy.c
+++ b/arch/metag/lib/usercopy.c
@@ -717,6 +717,8 @@ unsigned long __copy_user_zeroing(void *pdst, const void __user *psrc,
         if ((unsigned long) src & 1) {
                 __asm_copy_from_user_1(dst, src, retn);
                 n--;
+                if (retn)
+                        goto copy_exception_bytes;
         }
         if ((unsigned long) dst & 1) {
                 /* Worst case - byte copy */
@@ -730,6 +732,8 @@ unsigned long __copy_user_zeroing(void *pdst, const void __user *psrc,
         if (((unsigned long) src & 2) && n >= 2) {
                 __asm_copy_from_user_2(dst, src, retn);
                 n -= 2;
+                if (retn)
+                        goto copy_exception_bytes;
         }
         if ((unsigned long) dst & 2) {
                 /* Second worst case - word copy */
@@ -741,12 +745,6 @@ unsigned long __copy_user_zeroing(void *pdst, const void __user *psrc,
                 }
         }
 
-        /* We only need one check after the unalignment-adjustments,
-           because if both adjustments were done, either both or
-           neither reference had an exception.  */
-        if (retn != 0)
-                goto copy_exception_bytes;
-
 #ifdef USE_RAPF
         /* 64 bit copy loop */
         if (!(((unsigned long) src | (unsigned long) dst) & 7)) {