kasan: detect negative size in memory operation function

Patch series "fix the missing underflow in memory operation function", v4.

The patchset helps to produce a KASAN report when size is negative in
memory operation functions.  It is helpful for programmer to solve an
undefined behavior issue.  Patch 1 based on Dmitry's review and
suggestion, patch 2 is a test in order to verify the patch 1.

[1]https://bugzilla.kernel.org/show_bug.cgi?id=199341
[2]https://lore.kernel.org/linux-arm-kernel/[email protected]/

This patch (of 2):

KASAN missed detecting size is a negative number in memset(), memcpy(),
and memmove(), it will cause out-of-bounds bug.  So needs to be detected
by KASAN.

If size is a negative number, then it has a reason to be defined as
out-of-bounds bug type.  Casting negative numbers to size_t would indeed
turn up as a large size_t and its value will be larger than ULONG_MAX/2,
so that this can qualify as out-of-bounds.

KASAN report is shown below:

 BUG: KASAN: out-of-bounds in kmalloc_memmove_invalid_size+0x70/0xa0
 Read of size 18446744073709551608 at addr ffffff8069660904 by task cat/72

 CPU: 2 PID: 72 Comm: cat Not tainted 5.4.0-rc1-next-20191004ajb-00001-gdb8af2f372b2-dirty #1
 Hardware name: linux,dummy-virt (DT)
 Call trace:
  dump_backtrace+0x0/0x288
  show_stack+0x14/0x20
  dump_stack+0x10c/0x164
  print_address_description.isra.9+0x68/0x378
  __kasan_report+0x164/0x1a0
  kasan_report+0xc/0x18
  check_memory_region+0x174/0x1d0
  memmove+0x34/0x88
  kmalloc_memmove_invalid_size+0x70/0xa0

[1] https://bugzilla.kernel.org/show_bug.cgi?id=199341

[[email protected]: fix -Wdeclaration-after-statement warn]
  Link: http://lkml.kernel.org/r/[email protected]
[[email protected]: fix objtool warning]
  Link: http://lkml.kernel.org/r/[email protected]
Reported-by: kernel test robot <[email protected]>
Reported-by: Dmitry Vyukov <[email protected]>
Suggested-by: Dmitry Vyukov <[email protected]>
Signed-off-by: Walter Wu <[email protected]>
Signed-off-by: Qian Cai <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Reviewed-by: Dmitry Vyukov <[email protected]>
Reviewed-by: Andrey Ryabinin <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

Author: truhuan

include/linux/kasan.h

@@ -190,7 +190,7 @@ void kasan_init_tags(void);
 
 void *kasan_reset_tag(const void *addr);
 
-void kasan_report(unsigned long addr, size_t size,
+bool kasan_report(unsigned long addr, size_t size,
 		bool is_write, unsigned long ip);
 
 #else /* CONFIG_KASAN_SW_TAGS */

mm/kasan/common.c

@@ -105,7 +105,8 @@ EXPORT_SYMBOL(__kasan_check_write);
 #undef memset
 void *memset(void *addr, int c, size_t len)
 {
-	check_memory_region((unsigned long)addr, len, true, _RET_IP_);
+	if (!check_memory_region((unsigned long)addr, len, true, _RET_IP_))
+		return NULL;
 
 	return __memset(addr, c, len);
 }
@@ -114,8 +115,9 @@ void *memset(void *addr, int c, size_t len)
 #undef memmove
 void *memmove(void *dest, const void *src, size_t len)
 {
-	check_memory_region((unsigned long)src, len, false, _RET_IP_);
-	check_memory_region((unsigned long)dest, len, true, _RET_IP_);
+	if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
+	    !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
+		return NULL;
 
 	return __memmove(dest, src, len);
 }
@@ -124,8 +126,9 @@ void *memmove(void *dest, const void *src, size_t len)
 #undef memcpy
 void *memcpy(void *dest, const void *src, size_t len)
 {
-	check_memory_region((unsigned long)src, len, false, _RET_IP_);
-	check_memory_region((unsigned long)dest, len, true, _RET_IP_);
+	if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
+	    !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
+		return NULL;
 
 	return __memcpy(dest, src, len);
 }
@@ -634,12 +637,21 @@ void kasan_free_shadow(const struct vm_struct *vm)
 #endif
 
 extern void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip);
+extern bool report_enabled(void);
 
-void kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip)
+bool kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip)
 {
 	unsigned long flags = user_access_save();
-	__kasan_report(addr, size, is_write, ip);
+	bool ret = false;
+
+	if (likely(report_enabled())) {
+		__kasan_report(addr, size, is_write, ip);
+		ret = true;
+	}
+
 	user_access_restore(flags);
+
+	return ret;
 }
 
 #ifdef CONFIG_MEMORY_HOTPLUG

mm/kasan/generic.c

@@ -173,17 +173,18 @@ static __always_inline bool check_memory_region_inline(unsigned long addr,
 	if (unlikely(size == 0))
 		return true;
 
+	if (unlikely(addr + size < addr))
+		return !kasan_report(addr, size, write, ret_ip);
+
 	if (unlikely((void *)addr <
 		kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
-		kasan_report(addr, size, write, ret_ip);
-		return false;
+		return !kasan_report(addr, size, write, ret_ip);
 	}
 
 	if (likely(!memory_is_poisoned(addr, size)))
 		return true;
 
-	kasan_report(addr, size, write, ret_ip);
-	return false;
+	return !kasan_report(addr, size, write, ret_ip);
 }
 
 bool check_memory_region(unsigned long addr, size_t size, bool write,

mm/kasan/generic_report.c

@@ -110,6 +110,17 @@ static const char *get_wild_bug_type(struct kasan_access_info *info)
 
 const char *get_bug_type(struct kasan_access_info *info)
 {
+	/*
+	 * If access_size is a negative number, then it has reason to be
+	 * defined as out-of-bounds bug type.
+	 *
+	 * Casting negative numbers to size_t would indeed turn up as
+	 * a large size_t and its value will be larger than ULONG_MAX/2,
+	 * so that this can qualify as out-of-bounds.
+	 */
+	if (info->access_addr + info->access_size < info->access_addr)
+		return "out-of-bounds";
+
 	if (addr_has_shadow(info->access_addr))
 		return get_shadow_bug_type(info);
 	return get_wild_bug_type(info);

mm/kasan/kasan.h

@@ -153,7 +153,7 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,
 void *find_first_bad_addr(void *addr, size_t size);
 const char *get_bug_type(struct kasan_access_info *info);
 
-void kasan_report(unsigned long addr, size_t size,
+bool kasan_report(unsigned long addr, size_t size,
 		bool is_write, unsigned long ip);
 void kasan_report_invalid_free(void *object, unsigned long ip);
 

mm/kasan/report.c

@@ -446,7 +446,7 @@ static void print_shadow_for_address(const void *addr)
 	}
 }
 
-static bool report_enabled(void)
+bool report_enabled(void)
 {
 	if (current->kasan_depth)
 		return false;
@@ -478,9 +478,6 @@ void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned lon
 	void *untagged_addr;
 	unsigned long flags;
 
-	if (likely(!report_enabled()))
-		return;
-
 	disable_trace_on_warning();
 
 	tagged_addr = (void *)addr;

mm/kasan/tags.c

@@ -86,6 +86,9 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,
 	if (unlikely(size == 0))
 		return true;
 
+	if (unlikely(addr + size < addr))
+		return !kasan_report(addr, size, write, ret_ip);
+
 	tag = get_tag((const void *)addr);
 
 	/*
@@ -111,15 +114,13 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,
 	untagged_addr = reset_tag((const void *)addr);
 	if (unlikely(untagged_addr <
 			kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
-		kasan_report(addr, size, write, ret_ip);
-		return false;
+		return !kasan_report(addr, size, write, ret_ip);
 	}
 	shadow_first = kasan_mem_to_shadow(untagged_addr);
 	shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1);
 	for (shadow = shadow_first; shadow <= shadow_last; shadow++) {
 		if (*shadow != tag) {
-			kasan_report(addr, size, write, ret_ip);
-			return false;
+			return !kasan_report(addr, size, write, ret_ip);
 		}
 	}
 

mm/kasan/tags_report.c

@@ -60,6 +60,17 @@ const char *get_bug_type(struct kasan_access_info *info)
 	}
 
 #endif
+	/*
+	 * If access_size is a negative number, then it has reason to be
+	 * defined as out-of-bounds bug type.
+	 *
+	 * Casting negative numbers to size_t would indeed turn up as
+	 * a large size_t and its value will be larger than ULONG_MAX/2,
+	 * so that this can qualify as out-of-bounds.
+	 */
+	if (info->access_addr + info->access_size < info->access_addr)
+		return "out-of-bounds";
+
 	return "invalid-access";
 }