[PATCH 2/3] lib, uaccess: add failure injection to usercopy functions

[albert.linde@gmail.com]

From: Albert van der Linde <alinde@google.com>

To test fault-tolerance of usercopy accesses, introduce fault injection
in usercopy functions.

Adds failure injection to usercopy functions. If a failure is expected
we return either the failure or the total amount of bytes. As many
usercopy functions can fail partially, permit also partial failures:
e.g., copy_from_user can fail copying between 0 and n.

Signed-off-by: Albert van der Linde <alinde@google.com>
---
 include/linux/uaccess.h | 31 ++++++++++++++++++++++++++-----
 lib/iov_iter.c          | 20 +++++++++++++++++---
 lib/strncpy_from_user.c |  3 +++
 lib/usercopy.c          | 13 +++++++++++--
 4 files changed, 57 insertions(+), 10 deletions(-)

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 94b285411659..79e736077ef4 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -2,6 +2,7 @@
 #ifndef __LINUX_UACCESS_H__
 #define __LINUX_UACCESS_H__
 
+#include <linux/fault-inject-usercopy.h>
 #include <linux/instrumented.h>
 #include <linux/sched.h>
 #include <linux/thread_info.h>
@@ -82,10 +83,14 @@ __copy_from_user_inatomic(void *to, const void __user *from, unsigned long n)
 static __always_inline __must_check unsigned long
 __copy_from_user(void *to, const void __user *from, unsigned long n)
 {
+	long not_copied = should_fail_usercopy(n);
+
+	if (not_copied < 0)
+		not_copied = n;
 	might_fault();
 	instrument_copy_from_user(to, from, n);
 	check_object_size(to, n, false);
-	return raw_copy_from_user(to, from, n);
+	return not_copied + raw_copy_from_user(to, from, n - not_copied);
 }
 
 /**
@@ -104,18 +109,26 @@ __copy_from_user(void *to, const void __user *from, unsigned long n)
 static __always_inline __must_check unsigned long
 __copy_to_user_inatomic(void __user *to, const void *from, unsigned long n)
 {
+	long not_copied = should_fail_usercopy(n);
+
+	if (not_copied < 0)
+		not_copied = n;
 	instrument_copy_to_user(to, from, n);
 	check_object_size(from, n, true);
-	return raw_copy_to_user(to, from, n);
+	return not_copied + raw_copy_to_user(to, from, n - not_copied);
 }
 
 static __always_inline __must_check unsigned long
 __copy_to_user(void __user *to, const void *from, unsigned long n)
 {
+	long not_copied = should_fail_usercopy(n);
+
+	if (not_copied < 0)
+		not_copied = n;
 	might_fault();
 	instrument_copy_to_user(to, from, n);
 	check_object_size(from, n, true);
-	return raw_copy_to_user(to, from, n);
+	return not_copied + raw_copy_to_user(to, from, n - not_copied);
 }
 
 #ifdef INLINE_COPY_FROM_USER
@@ -123,10 +136,14 @@ static inline __must_check unsigned long
 _copy_from_user(void *to, const void __user *from, unsigned long n)
 {
 	unsigned long res = n;
+	long not_copied = should_fail_usercopy(n);
+
+	if (not_copied < 0)
+		not_copied = n;
 	might_fault();
 	if (likely(access_ok(from, n))) {
 		instrument_copy_from_user(to, from, n);
-		res = raw_copy_from_user(to, from, n);
+		res = not_copied + raw_copy_from_user(to, from, n - not_copied);
 	}
 	if (unlikely(res))
 		memset(to + (n - res), 0, res);
@@ -141,10 +158,14 @@ _copy_from_user(void *, const void __user *, unsigned long);
 static inline __must_check unsigned long
 _copy_to_user(void __user *to, const void *from, unsigned long n)
 {
+	long not_copied = should_fail_usercopy(n);
+
+	if (not_copied < 0)
+		not_copied = n;
 	might_fault();
 	if (access_ok(to, n)) {
 		instrument_copy_to_user(to, from, n);
-		n = raw_copy_to_user(to, from, n);
+		n = not_copied + raw_copy_to_user(to, from, n - not_copied);
 	}
 	return n;
 }
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 5e40786c8f12..c55c9bff9b0c 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -2,6 +2,7 @@
 #include <crypto/hash.h>
 #include <linux/export.h>
 #include <linux/bvec.h>
+#include <linux/fault-inject-usercopy.h>
 #include <linux/uio.h>
 #include <linux/pagemap.h>
 #include <linux/slab.h>
@@ -139,18 +140,26 @@
 
 static int copyout(void __user *to, const void *from, size_t n)
 {
+	long not_copied = should_fail_usercopy(n);
+
+	if (not_copied < 0)
+		return not_copied;
 	if (access_ok(to, n)) {
 		instrument_copy_to_user(to, from, n);
-		n = raw_copy_to_user(to, from, n);
+		n = not_copied + raw_copy_to_user(to, from, n - not_copied);
 	}
 	return n;
 }
 
 static int copyin(void *to, const void __user *from, size_t n)
 {
+	long not_copied = should_fail_usercopy(n);
+
+	if (not_copied < 0)
+		return not_copied;
 	if (access_ok(from, n)) {
 		instrument_copy_from_user(to, from, n);
-		n = raw_copy_from_user(to, from, n);
+		n = not_copied + raw_copy_from_user(to, from, n - not_copied);
 	}
 	return n;
 }
@@ -640,9 +649,14 @@ EXPORT_SYMBOL(_copy_to_iter);
 #ifdef CONFIG_ARCH_HAS_UACCESS_MCSAFE
 static int copyout_mcsafe(void __user *to, const void *from, size_t n)
 {
+	long not_copied = should_fail_usercopy(n);
+
+	if (not_copied < 0)
+		return not_copied;
 	if (access_ok(to, n)) {
 		instrument_copy_to_user(to, from, n);
-		n = copy_to_user_mcsafe((__force void *) to, from, n);
+		n = not_copied + copy_to_user_mcsafe((__force void *) to,
+			       from, n - not_copied);
 	}
 	return n;
 }
diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
index 34696a348864..f65973007931 100644
--- a/lib/strncpy_from_user.c
+++ b/lib/strncpy_from_user.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/compiler.h>
 #include <linux/export.h>
+#include <linux/fault-inject-usercopy.h>
 #include <linux/kasan-checks.h>
 #include <linux/thread_info.h>
 #include <linux/uaccess.h>
@@ -101,6 +102,8 @@ long strncpy_from_user(char *dst, const char __user *src, long count)
 	might_fault();
 	if (unlikely(count <= 0))
 		return 0;
+	if (should_fail_usercopy(count))
+		return -EFAULT;
 
 	max_addr = user_addr_max();
 	src_addr = (unsigned long)untagged_addr(src);
diff --git a/lib/usercopy.c b/lib/usercopy.c
index b26509f112f9..e79716b4634b 100644
--- a/lib/usercopy.c
+++ b/lib/usercopy.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/bitops.h>
+#include <linux/fault-inject-usercopy.h>
 #include <linux/instrumented.h>
 #include <linux/uaccess.h>
 
@@ -9,10 +10,14 @@
 unsigned long _copy_from_user(void *to, const void __user *from, unsigned long n)
 {
 	unsigned long res = n;
+	long not_copied = should_fail_usercopy(n);
+
+	if (not_copied < 0)
+		not_copied = n;
 	might_fault();
 	if (likely(access_ok(from, n))) {
 		instrument_copy_from_user(to, from, n);
-		res = raw_copy_from_user(to, from, n);
+		res = not_copied + raw_copy_from_user(to, from, n - not_copied);
 	}
 	if (unlikely(res))
 		memset(to + (n - res), 0, res);
@@ -24,10 +29,14 @@ EXPORT_SYMBOL(_copy_from_user);
 #ifndef INLINE_COPY_TO_USER
 unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n)
 {
+	long not_copied = should_fail_usercopy(n);
+
+	if (not_copied < 0)
+		not_copied = n;
 	might_fault();
 	if (likely(access_ok(to, n))) {
 		instrument_copy_to_user(to, from, n);
-		n = raw_copy_to_user(to, from, n);
+		n = not_copied + raw_copy_to_user(to, from, n - not_copied);
 	}
 	return n;
 }
-- 
2.28.0.297.g1956fa8f8d-goog