[PATCH v2 3/9] metag/usercopy: Add early abort to copy_to_user

[James Hogan <james.hogan@imgtec.com>]

When copying to userland on Meta, if any faults are encountered
immediately abort the copy instead of continuing on and repeatedly
faulting, and worse potentially copying further bytes successfully to
subsequent valid pages.

Fixes: 373cd784d0fc ("metag: Memory handling")
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-metag@vger.kernel.org
Cc: stable@vger.kernel.org
---
 arch/metag/lib/usercopy.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+), 0 deletions(-)

diff --git a/arch/metag/lib/usercopy.c b/arch/metag/lib/usercopy.c
index a6ced9691ddb..714d8562aa20 100644
--- a/arch/metag/lib/usercopy.c
+++ b/arch/metag/lib/usercopy.c
@@ -538,23 +538,31 @@ unsigned long __copy_user(void __user *pdst, const void *psrc,
 	if ((unsigned long) src & 1) {
 		__asm_copy_to_user_1(dst, src, retn);
 		n--;
+		if (retn)
+			return retn + n;
 	}
 	if ((unsigned long) dst & 1) {
 		/* Worst case - byte copy */
 		while (n > 0) {
 			__asm_copy_to_user_1(dst, src, retn);
 			n--;
+			if (retn)
+				return retn + n;
 		}
 	}
 	if (((unsigned long) src & 2) && n >= 2) {
 		__asm_copy_to_user_2(dst, src, retn);
 		n -= 2;
+		if (retn)
+			return retn + n;
 	}
 	if ((unsigned long) dst & 2) {
 		/* Second worst case - word copy */
 		while (n >= 2) {
 			__asm_copy_to_user_2(dst, src, retn);
 			n -= 2;
+			if (retn)
+				return retn + n;
 		}
 	}
 
@@ -569,6 +577,8 @@ unsigned long __copy_user(void __user *pdst, const void *psrc,
 		while (n >= 8) {
 			__asm_copy_to_user_8x64(dst, src, retn);
 			n -= 8;
+			if (retn)
+				return retn + n;
 		}
 	}
 	if (n >= RAPF_MIN_BUF_SIZE) {
@@ -581,6 +591,8 @@ unsigned long __copy_user(void __user *pdst, const void *psrc,
 		while (n >= 8) {
 			__asm_copy_to_user_8x64(dst, src, retn);
 			n -= 8;
+			if (retn)
+				return retn + n;
 		}
 	}
 #endif
@@ -588,11 +600,15 @@ unsigned long __copy_user(void __user *pdst, const void *psrc,
 	while (n >= 16) {
 		__asm_copy_to_user_16(dst, src, retn);
 		n -= 16;
+		if (retn)
+			return retn + n;
 	}
 
 	while (n >= 4) {
 		__asm_copy_to_user_4(dst, src, retn);
 		n -= 4;
+		if (retn)
+			return retn + n;
 	}
 
 	switch (n) {
@@ -609,6 +625,10 @@ unsigned long __copy_user(void __user *pdst, const void *psrc,
 		break;
 	}
 
+	/*
+	 * If we get here, retn correctly reflects the number of failing
+	 * bytes.
+	 */
 	return retn;
 }
 EXPORT_SYMBOL(__copy_user);
-- 
git-series 0.8.10