btrfs: add separate bounds checker for set/get helpers

The bounds checking is now done in map_private_extent_buffer but that
will be removed in following patches and some sanity checks should still
be done.

There are two separate checks to see the kind of out of bounds access:
partial (start offset is in the buffer) or complete (both start and end
are out).
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/struct-funcs.c

@@ -17,6 +17,27 @@ static inline void put_unaligned_le8(u8 val, void *p)
        *(u8 *)p = val;
 }
 
+static bool check_setget_bounds(const struct extent_buffer *eb,
+				const void *ptr, unsigned off, int size)
+{
+	const unsigned long member_offset = (unsigned long)ptr + off;
+
+	if (member_offset > eb->len) {
+		btrfs_warn(eb->fs_info,
+	"bad eb member start: ptr 0x%lx start %llu member offset %lu size %d",
+			(unsigned long)ptr, eb->start, member_offset, size);
+		return false;
+	}
+	if (member_offset + size > eb->len) {
+		btrfs_warn(eb->fs_info,
+	"bad eb member end: ptr 0x%lx start %llu member offset %lu size %d",
+			(unsigned long)ptr, eb->start, member_offset, size);
+		return false;
+	}
+
+	return true;
+}
+
 /*
  * this is some deeply nasty code.
  *
@@ -53,6 +74,7 @@ u##bits btrfs_get_token_##bits(struct btrfs_map_token *token,		\
 									\
 	ASSERT(token);							\
 	ASSERT(token->kaddr);						\
+	ASSERT(check_setget_bounds(token->eb, ptr, off, size));		\
 	if (token->offset <= offset &&					\
 	   (token->offset + PAGE_SIZE >= offset + size)) {	\
 		kaddr = token->kaddr;					\
@@ -87,6 +109,7 @@ u##bits btrfs_get_##bits(const struct extent_buffer *eb,		\
 	int size = sizeof(u##bits);					\
 	u##bits res;							\
 									\
+	ASSERT(check_setget_bounds(eb, ptr, off, size));		\
 	err = map_private_extent_buffer(eb, offset, size,		\
 					&kaddr, &map_start, &map_len);	\
 	if (err) {							\
@@ -114,6 +137,7 @@ void btrfs_set_token_##bits(struct btrfs_map_token *token,		\
 									\
 	ASSERT(token);							\
 	ASSERT(token->kaddr);						\
+	ASSERT(check_setget_bounds(token->eb, ptr, off, size));		\
 	if (token->offset <= offset &&					\
 	   (token->offset + PAGE_SIZE >= offset + size)) {	\
 		kaddr = token->kaddr;					\
@@ -147,6 +171,7 @@ void btrfs_set_##bits(struct extent_buffer *eb, void *ptr,		\
 	unsigned long map_len;						\
 	int size = sizeof(u##bits);					\
 									\
+	ASSERT(check_setget_bounds(eb, ptr, off, size));		\
 	err = map_private_extent_buffer(eb, offset, size,		\
 			&kaddr, &map_start, &map_len);			\
 	if (err) {							\