bcache: fix stack corruption by PRECEDING_KEY()

[thirdparty/kernel/stable.git] / drivers / md / bcache / bset.h

diff --git a/drivers/md/bcache/bset.h b/drivers/md/bcache/bset.h
index bac76aabca6d7977abfecfaee4d884719f3699f4..c71365e7c1fac7fc87b051b10e8697edbe29f8c4 100644 (file)
--- a/drivers/md/bcache/bset.h
+++ b/drivers/md/bcache/bset.h
@@ -434,20 +434,26 @@ static inline bool bch_cut_back(const struct bkey *where, struct bkey *k)
        return __bch_cut_back(where, k);
 }
 
-#define PRECEDING_KEY(_k)                                      \
-({                                                             \
-       struct bkey *_ret = NULL;                               \
-                                                               \
-       if (KEY_INODE(_k) || KEY_OFFSET(_k)) {                  \
-               _ret = &KEY(KEY_INODE(_k), KEY_OFFSET(_k), 0);  \
-                                                               \
-               if (!_ret->low)                                 \
-                       _ret->high--;                           \
-               _ret->low--;                                    \
-       }                                                       \
-                                                               \
-       _ret;                                                   \
-})
+/*
+ * Pointer '*preceding_key_p' points to a memory object to store preceding
+ * key of k. If the preceding key does not exist, set '*preceding_key_p' to
+ * NULL. So the caller of preceding_key() needs to take care of memory
+ * which '*preceding_key_p' pointed to before calling preceding_key().
+ * Currently the only caller of preceding_key() is bch_btree_insert_key(),
+ * and it points to an on-stack variable, so the memory release is handled
+ * by stackframe itself.
+ */
+static inline void preceding_key(struct bkey *k, struct bkey **preceding_key_p)
+{
+       if (KEY_INODE(k) || KEY_OFFSET(k)) {
+               (**preceding_key_p) = KEY(KEY_INODE(k), KEY_OFFSET(k), 0);
+               if (!(*preceding_key_p)->low)
+                       (*preceding_key_p)->high--;
+               (*preceding_key_p)->low--;
+       } else {
+               (*preceding_key_p) = NULL;
+       }
+}
 
 static inline bool bch_ptr_invalid(struct btree_keys *b, const struct bkey *k)
 {