• Coly Li's avatar
    bcache: fix stack corruption by PRECEDING_KEY() · 31b90956
    Coly Li authored
    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: 0eacac22 ("bcache: PRECEDING_KEY()")
    Signed-off-by: default avatarColy Li <colyli@suse.de>
    Reviewed-by: default avatarRolf Fokkens <rolf@rolffokkens.nl>
    Reviewed-by: default avatarPierre JUHEN <pierre.juhen@orange.fr>
    Tested-by: default avatarShenghui Wang <shhuiw@foxmail.com>
    Tested-by: default avatarPierre 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: default avatarJens Axboe <axboe@kernel.dk>
    31b90956
bset.h 19 KB