[PULL 15/45] linux-user: Check for overflow in access_ok

[Peter Maydell <peter.maydell@linaro.org>]

From: Richard Henderson <richard.henderson@linaro.org>

Verify that addr + size - 1 does not wrap around.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210210000223.884088-7-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 linux-user/qemu.h | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index 17aa9921657..441ba6a78bb 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -491,12 +491,19 @@ extern unsigned long guest_stack_size;
 #define VERIFY_READ 0
 #define VERIFY_WRITE 1 /* implies read access */
 
-static inline int access_ok(int type, abi_ulong addr, abi_ulong size)
+static inline bool access_ok(int type, abi_ulong addr, abi_ulong size)
 {
-    return guest_addr_valid(addr) &&
-           (size == 0 || guest_addr_valid(addr + size - 1)) &&
-           page_check_range((target_ulong)addr, size,
-                            (type == VERIFY_READ) ? PAGE_READ : (PAGE_READ | PAGE_WRITE)) == 0;
+    if (!guest_addr_valid(addr)) {
+        return false;
+    }
+    if (size != 0 &&
+        (addr + size - 1 < addr ||
+         !guest_addr_valid(addr + size - 1))) {
+        return false;
+    }
+    return page_check_range((target_ulong)addr, size,
+                            (type == VERIFY_READ) ? PAGE_READ :
+                            (PAGE_READ | PAGE_WRITE)) == 0;
 }
 
 /* NOTE __get_user and __put_user use host pointers and don't check access.
-- 
2.20.1