[PATCH] fortify: Use WARN instead of BUG for now

Kees Cook
2017-07-26T03:50:40Z

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@gmail.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Kees Cook <keescook@chromium.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