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Date: Mon, 13 Feb 2017 11:28:30 -0800
From: Kees Cook <keescook@...omium.org>
To: linux-kernel@...r.kernel.org
Cc: kernel-hardening@...ts.openwall.com, Hoeun Ryu <hoeun.ryu@...il.com>
Subject: [PATCH] usercopy: Adjust tests to deal with SMAP/PAN
Under SMAP/PAN/etc, we cannot write directly to userspace memory, so
this rearranges the test bytes to get written through copy_to_user().
Additionally fixes a small memory leak on user memory allocation failure,
and drops the bad copy_from_user() test that would trigger a memcpy()
against userspace on failure.
Signed-off-by: Kees Cook <keescook@...omium.org>
---
lib/test_user_copy.c | 45 ++++++++++++++++++++++++++++++++-------------
1 file changed, 32 insertions(+), 13 deletions(-)
diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c
index 54bd898e356f..ac3a60ba9331 100644
--- a/lib/test_user_copy.c
+++ b/lib/test_user_copy.c
@@ -49,8 +49,8 @@ static int __init test_user_copy_init(void)
zerokmem = kzalloc(PAGE_SIZE * 2, GFP_KERNEL);
if (!zerokmem) {
- kfree(kmem);
- return -ENOMEM;
+ ret = -ENOMEM;
+ goto out_kmem;
}
user_addr = vm_mmap(NULL, 0, PAGE_SIZE * 2,
@@ -58,14 +58,16 @@ static int __init test_user_copy_init(void)
MAP_ANONYMOUS | MAP_PRIVATE, 0);
if (user_addr >= (unsigned long)(TASK_SIZE)) {
pr_warn("Failed to allocate user memory\n");
- kfree(kmem);
- return -ENOMEM;
+ ret = -ENOMEM;
+ goto out_zerokmem;
}
usermem = (char __user *)user_addr;
bad_usermem = (char *)user_addr;
- /* Legitimate usage: none of these should fail. */
+ /*
+ * Legitimate usage: none of these copies should fail.
+ */
ret |= test(copy_from_user(kmem, usermem, PAGE_SIZE),
"legitimate copy_from_user failed");
ret |= test(copy_to_user(usermem, kmem, PAGE_SIZE),
@@ -75,36 +77,53 @@ static int __init test_user_copy_init(void)
ret |= test(put_user(value, (unsigned long __user *)usermem),
"legitimate put_user failed");
- /* Invalid usage: none of these should succeed. */
+ /*
+ * Invalid usage: none of these copies should succeed.
+ */
+
+ /* Prepare kernel memory with check values. */
memset(kmem, 0x5A, PAGE_SIZE);
+ memset(kmem + PAGE_SIZE, 0x5B, PAGE_SIZE);
+
+ /* Reject kernel-to-kernel copies through copy_from_user(). */
ret |= test(!copy_from_user(kmem, (char __user *)(kmem + PAGE_SIZE),
PAGE_SIZE),
"illegal all-kernel copy_from_user passed");
+
+ /* Destination half of buffer should have been zeroed. */
ret |= test(memcmp(zerokmem, kmem, PAGE_SIZE),
"zeroing failure for illegal all-kernel copy_from_user");
- memset(bad_usermem, 0x5A, PAGE_SIZE);
+
+#if 0
+ /*
+ * When running with SMAP/PAN/etc, this will Oops the kernel
+ * due to the zeroing of userspace memory on failure. This needs
+ * to be tested in LKDTM instead, since this test module does not
+ * expect to explode.
+ */
ret |= test(!copy_from_user(bad_usermem, (char __user *)kmem,
PAGE_SIZE),
"illegal reversed copy_from_user passed");
- ret |= test(memcmp(zerokmem, bad_usermem, PAGE_SIZE),
- "zeroing failure for illegal reversed copy_from_user");
+#endif
ret |= test(!copy_to_user((char __user *)kmem, kmem + PAGE_SIZE,
PAGE_SIZE),
"illegal all-kernel copy_to_user passed");
ret |= test(!copy_to_user((char __user *)kmem, bad_usermem,
PAGE_SIZE),
"illegal reversed copy_to_user passed");
- memset(kmem, 0x5A, PAGE_SIZE);
+
+ value = 0x5A;
ret |= test(!get_user(value, (unsigned long __user *)kmem),
"illegal get_user passed");
- ret |= test(memcmp(zerokmem, kmem, sizeof(value)),
- "zeroing failure for illegal get_user");
+ ret |= test(value != 0, "zeroing failure for illegal get_user");
ret |= test(!put_user(value, (unsigned long __user *)kmem),
"illegal put_user passed");
vm_munmap(user_addr, PAGE_SIZE * 2);
- kfree(kmem);
+out_zerokmem:
kfree(zerokmem);
+out_kmem:
+ kfree(kmem);
if (ret == 0) {
pr_info("tests passed.\n");
--
2.7.4
--
Kees Cook
Pixel Security
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