[PATCH 3.10 202/250] metag/usercopy: Fix alignment error checking

[Willy Tarreau]

From: James Hogan <james.hogan@xxxxxxxxxx>

commit 2257211942bbbf6c798ab70b487d7e62f7835a1a upstream.

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@xxxxxxxxxx>
Cc: linux-metag@xxxxxxxxxxxxxxx
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Signed-off-by: Willy Tarreau <w@xxxxxx>
---
 arch/metag/lib/usercopy.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/arch/metag/lib/usercopy.c b/arch/metag/lib/usercopy.c
index b3ebfe9..a26c889 100644
--- a/arch/metag/lib/usercopy.c
+++ b/arch/metag/lib/usercopy.c
@@ -830,6 +830,8 @@ 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 */
@@ -843,6 +845,8 @@ 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 */
@@ -854,12 +858,6 @@ 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)) {
-- 
2.8.0.rc2.1.gbe9624a