[PATCH 6/7] test_user_copy: Check user string accessors

[James Hogan]

Add basic success/failure checking of the user string functions which
copy or find the length of userland strings.

The following cases are checked:
- strncpy_from_user() with legitimate user to kernel addresses, illegal
  all-kernel and reversed addresses, and legitimate all-kernel
  addresses.
- strnlen_user()/strlen_user() with a legitimate user address, an
  illegal kernel address, and a legitimate kernel address.

This caught a bug in the MIPS Enhanced Virtual Memory (EVA)
implementation:
test_user_copy: illegal strlen_user passed

Due to strlen_user() accidentally always using normal kernel loads, and
the EVA user/kernel address ranges overlapping.

New tests:
- legitimate strncpy_from_user
- legitimate strnlen_user
- legitimate strlen_user
- illegal all-kernel strncpy_from_user
- illegal reversed strncpy_from_user
- illegal strnlen_user
- illegal strlen_user
- legitimate all-kernel strncpy_from_user
- legitimate kernel strnlen_user
- legitimate kernel strlen_user

Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
 lib/test_user_copy.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c
index 6cbdb0a15ca2..6d05ec5f6cfa 100644
--- a/lib/test_user_copy.c
+++ b/lib/test_user_copy.c
@@ -72,6 +72,12 @@ static int __init test_user_copy_init(void)
 		    "legitimate put_user failed");
 	ret |= test(clear_user(usermem, PAGE_SIZE) != 0,
 		    "legitimate clear_user passed");
+	ret |= test(strncpy_from_user(kmem, usermem, PAGE_SIZE) < 0,
+		    "legitimate strncpy_from_user failed");
+	ret |= test(strnlen_user(usermem, PAGE_SIZE) == 0,
+		    "legitimate strnlen_user failed");
+	ret |= test(strlen_user(usermem) == 0,
+		    "legitimate strlen_user failed");
 
 	ret |= test(!access_ok(VERIFY_READ, usermem, PAGE_SIZE * 2),
 		    "legitimate access_ok VERIFY_READ failed");
@@ -122,6 +128,16 @@ static int __init test_user_copy_init(void)
 		    "illegal put_user passed");
 	ret |= test(clear_user((char __user *)kmem, PAGE_SIZE) != PAGE_SIZE,
 		    "illegal kernel clear_user passed");
+	ret |= test(strncpy_from_user(kmem, (char __user *)(kmem + PAGE_SIZE),
+				      PAGE_SIZE) >= 0,
+		    "illegal all-kernel strncpy_from_user passed");
+	ret |= test(strncpy_from_user(bad_usermem, (char __user *)kmem,
+				      PAGE_SIZE) >= 0,
+		    "illegal reversed strncpy_from_user passed");
+	ret |= test(strnlen_user((char __user *)kmem, PAGE_SIZE) != 0,
+		    "illegal strnlen_user passed");
+	ret |= test(strlen_user((char __user *)kmem) != 0,
+		    "illegal strlen_user passed");
 
 	/*
 	 * If unchecked user accesses (__*) on this architecture cannot access
@@ -201,6 +217,13 @@ static int __init test_user_copy_init(void)
 		    "legitimate kernel put_user failed");
 	ret |= test(clear_user((char __user *)kmem, PAGE_SIZE) != 0,
 		    "legitimate kernel clear_user failed");
+	ret |= test(strncpy_from_user(kmem, (char __user *)(kmem + PAGE_SIZE),
+				      PAGE_SIZE) < 0,
+		    "legitimate all-kernel strncpy_from_user failed");
+	ret |= test(strnlen_user((char __user *)kmem, PAGE_SIZE) == 0,
+		    "legitimate kernel strnlen_user failed");
+	ret |= test(strlen_user((char __user *)kmem) == 0,
+		    "legitimate kernel strlen_user failed");
 
 	ret |= test(!access_ok(VERIFY_READ, (char __user *)kmem, PAGE_SIZE * 2),
 		    "legitimate kernel access_ok VERIFY_READ failed");
-- 
2.3.6

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