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bcache: fix stack corruption by PRECEDING_KEY() 

Recently people report bcache code compiled with gcc9 is broken, one of
the buggy behavior I observe is that two adjacent 4KB I/Os should merge
into one but they don't. Finally it turns out to be a stack corruption
caused by macro PRECEDING_KEY().

See how PRECEDING_KEY() is defined in bset.h,
437 #define PRECEDING_KEY(_k)                                       \
438 ({                                                              \
439         struct bkey *_ret = NULL;                               \
440                                                                 \
441         if (KEY_INODE(_k) || KEY_OFFSET(_k)) {                  \
442                 _ret = &KEY(KEY_INODE(_k), KEY_OFFSET(_k), 0);  \
443                                                                 \
444                 if (!_ret->low)                                 \
445                         _ret->high--;                           \
446                 _ret->low--;                                    \
447         }                                                       \
448                                                                 \
449         _ret;                                                   \
450 })

At line 442, _ret points to address of a on-stack variable combined by
KEY(), the life range of this on-stack variable is in line 442-446,
once _ret is returned to bch_btree_insert_key(), the returned address
points to an invalid stack address and this address is overwritten in
the following called bch_btree_iter_init(). Then argument 'search' of
bch_btree_iter_init() points to some address inside stackframe of
bch_btree_iter_init(), exact address depends on how the compiler
allocates stack space. Now the stack is corrupted.

Fixes: 0eacac2203 ("bcache: PRECEDING_KEY()")
Signed-off-by: Coly Li <colyli@suse.de>
Reviewed-by: Rolf Fokkens <rolf@rolffokkens.nl>
Reviewed-by: Pierre JUHEN <pierre.juhen@orange.fr>
Tested-by: Shenghui Wang <shhuiw@foxmail.com>
Tested-by: Pierre JUHEN <pierre.juhen@orange.fr>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: Nix <nix@esperi.org.uk>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Coly Li 2019-06-10 06:13:34 +08:00 committed by Jens Axboe
parent c326f846eb
commit 31b90956b1
2 changed files with 33 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
drivers/md/bcache/bset.c
View File

@ -887,12 +887,22 @@ unsigned int bch_btree_insert_key(struct btree_keys *b, struct bkey *k,
struct bset *i = bset_tree_last(b)->data;
struct bkey *m, *prev = NULL;
struct btree_iter iter;
struct bkey preceding_key_on_stack = ZERO_KEY;
struct bkey *preceding_key_p = &preceding_key_on_stack;
BUG_ON(b->ops->is_extents && !KEY_SIZE(k));
m = bch_btree_iter_init(b, &iter, b->ops->is_extents
? PRECEDING_KEY(&START_KEY(k))
: PRECEDING_KEY(k));
/*
* If k has preceding key, preceding_key_p will be set to address
* of k's preceding key; otherwise preceding_key_p will be set
* to NULL inside preceding_key().
*/
if (b->ops->is_extents)
preceding_key(&START_KEY(k), &preceding_key_p);
else
preceding_key(k, &preceding_key_p);
m = bch_btree_iter_init(b, &iter, preceding_key_p);
if (b->ops->insert_fixup(b, k, &iter, replace_key))
return status;

34
drivers/md/bcache/bset.h
View File

@ -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)
{