Date:   Tue, 25 Jul 2017 20:50:36 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Daniel Micay <danielmicay@...il.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] fortify: Use WARN instead of BUG for now

While CONFIG_FORTIFY_SOURCE continues to shake out, don't unconditionally
use BUG(), opting instead for WARN(). At the same time, expand the runtime
detection to provide a better hint about what went wrong.

Cc: Daniel Micay <danielmicay@...il.com>
Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
Sending to akpm, since fortify went through -mm originally.
---
 include/linux/string.h | 48 ++++++++++++++++++++++++++++++------------------
 lib/string.c           | 19 +++++++++++++++----
 2 files changed, 45 insertions(+), 22 deletions(-)

diff --git a/include/linux/string.h b/include/linux/string.h
index a467e617eeb0..97468047b965 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -197,7 +197,10 @@ static inline const char *kbasename(const char *path)
 #define __FORTIFY_INLINE extern __always_inline __attribute__((gnu_inline))
 #define __RENAME(x) __asm__(#x)
 
-void fortify_panic(const char *name) __noreturn __cold;
+void fortify_read_overflow(const char *func) __cold;
+void fortify_read_overflow2(const char *func) __cold;
+void fortify_write_overflow(const char *func) __cold;
+
 void __read_overflow(void) __compiletime_error("detected read beyond size of object passed as 1st parameter");
 void __read_overflow2(void) __compiletime_error("detected read beyond size of object passed as 2nd parameter");
 void __write_overflow(void) __compiletime_error("detected write beyond size of object passed as 1st parameter");
@@ -209,7 +212,7 @@ __FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size)
 	if (__builtin_constant_p(size) && p_size < size)
 		__write_overflow();
 	if (p_size < size)
-		fortify_panic(__func__);
+		fortify_write_overflow(__func__);
 	return __builtin_strncpy(p, q, size);
 }
 
@@ -219,7 +222,7 @@ __FORTIFY_INLINE char *strcat(char *p, const char *q)
 	if (p_size == (size_t)-1)
 		return __builtin_strcat(p, q);
 	if (strlcat(p, q, p_size) >= p_size)
-		fortify_panic(__func__);
+		fortify_write_overflow(__func__);
 	return p;
 }
 
@@ -231,7 +234,7 @@ __FORTIFY_INLINE __kernel_size_t strlen(const char *p)
 		return __builtin_strlen(p);
 	ret = strnlen(p, p_size);
 	if (p_size <= ret)
-		fortify_panic(__func__);
+		fortify_read_overflow(__func__);
 	return ret;
 }
 
@@ -241,7 +244,7 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char *p, __kernel_size_t maxlen)
 	size_t p_size = __builtin_object_size(p, 0);
 	__kernel_size_t ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size);
 	if (p_size <= ret && maxlen != ret)
-		fortify_panic(__func__);
+		fortify_read_overflow(__func__);
 	return ret;
 }
 
@@ -260,7 +263,7 @@ __FORTIFY_INLINE size_t strlcpy(char *p, const char *q, size_t size)
 		if (__builtin_constant_p(len) && len >= p_size)
 			__write_overflow();
 		if (len >= p_size)
-			fortify_panic(__func__);
+			fortify_write_overflow(__func__);
 		__builtin_memcpy(p, q, len);
 		p[len] = '\0';
 	}
@@ -278,7 +281,7 @@ __FORTIFY_INLINE char *strncat(char *p, const char *q, __kernel_size_t count)
 	p_len = strlen(p);
 	copy_len = strnlen(q, count);
 	if (p_size < p_len + copy_len + 1)
-		fortify_panic(__func__);
+		fortify_write_overflow(__func__);
 	__builtin_memcpy(p + p_len, q, copy_len);
 	p[p_len + copy_len] = '\0';
 	return p;
@@ -290,7 +293,7 @@ __FORTIFY_INLINE void *memset(void *p, int c, __kernel_size_t size)
 	if (__builtin_constant_p(size) && p_size < size)
 		__write_overflow();
 	if (p_size < size)
-		fortify_panic(__func__);
+		fortify_write_overflow(__func__);
 	return __builtin_memset(p, c, size);
 }
 
@@ -303,9 +306,12 @@ __FORTIFY_INLINE void *memcpy(void *p, const void *q, __kernel_size_t size)
 			__write_overflow();
 		if (q_size < size)
 			__read_overflow2();
+	} else {
+		if (p_size < size)
+			fortify_write_overflow(__func__);
+		if (q_size < size)
+			fortify_read_overflow2(__func__);
 	}
-	if (p_size < size || q_size < size)
-		fortify_panic(__func__);
 	return __builtin_memcpy(p, q, size);
 }
 
@@ -318,9 +324,12 @@ __FORTIFY_INLINE void *memmove(void *p, const void *q, __kernel_size_t size)
 			__write_overflow();
 		if (q_size < size)
 			__read_overflow2();
+	} else {
+		if (p_size < size)
+			fortify_write_overflow(__func__);
+		if (q_size < size)
+			fortify_read_overflow2(__func__);
 	}
-	if (p_size < size || q_size < size)
-		fortify_panic(__func__);
 	return __builtin_memmove(p, q, size);
 }
 
@@ -331,7 +340,7 @@ __FORTIFY_INLINE void *memscan(void *p, int c, __kernel_size_t size)
 	if (__builtin_constant_p(size) && p_size < size)
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(__func__);
+		fortify_read_overflow(__func__);
 	return __real_memscan(p, c, size);
 }
 
@@ -344,9 +353,12 @@ __FORTIFY_INLINE int memcmp(const void *p, const void *q, __kernel_size_t size)
 			__read_overflow();
 		if (q_size < size)
 			__read_overflow2();
+	} else {
+		if (p_size < size)
+			fortify_read_overflow(__func__);
+		if (q_size < size)
+			fortify_read_overflow2(__func__);
 	}
-	if (p_size < size || q_size < size)
-		fortify_panic(__func__);
 	return __builtin_memcmp(p, q, size);
 }
 
@@ -356,7 +368,7 @@ __FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size)
 	if (__builtin_constant_p(size) && p_size < size)
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(__func__);
+		fortify_read_overflow(__func__);
 	return __builtin_memchr(p, c, size);
 }
 
@@ -367,7 +379,7 @@ __FORTIFY_INLINE void *memchr_inv(const void *p, int c, size_t size)
 	if (__builtin_constant_p(size) && p_size < size)
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(__func__);
+		fortify_read_overflow(__func__);
 	return __real_memchr_inv(p, c, size);
 }
 
@@ -378,7 +390,7 @@ __FORTIFY_INLINE void *kmemdup(const void *p, size_t size, gfp_t gfp)
 	if (__builtin_constant_p(size) && p_size < size)
 		__read_overflow();
 	if (p_size < size)
-		fortify_panic(__func__);
+		fortify_read_overflow(__func__);
 	return __real_kmemdup(p, size, gfp);
 }
 
diff --git a/lib/string.c b/lib/string.c
index ebbb99c775bd..0fb68ec9a455 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -979,9 +979,20 @@ char *strreplace(char *s, char old, char new)
 }
 EXPORT_SYMBOL(strreplace);
 
-void fortify_panic(const char *name)
+void fortify_read_overflow(const char *func)
 {
-	pr_emerg("detected buffer overflow in %s\n", name);
-	BUG();
+	WARN(1, "detected read beyond size of object passed as 1st parameter in %s\n", func);
 }
-EXPORT_SYMBOL(fortify_panic);
+EXPORT_SYMBOL(fortify_read_overflow);
+
+void fortify_read_overflow2(const char *func)
+{
+	WARN(1, "detected read beyond size of object passed as 2nd parameter in %s\n", func);
+}
+EXPORT_SYMBOL(fortify_read_overflow2);
+
+void fortify_write_overflow(const char *func)
+{
+	WARN(1, "detected write beyond size of object passed as 1st parameter in %s\n", func);
+}
+EXPORT_SYMBOL(fortify_write_overflow);
-- 
2.7.4


-- 
Kees Cook
Pixel Security

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