md/raid10: initialize r10_bio->read_slot before use.

commit 93decc563637c4288380912eac0eb42fb246cc04 upstream.

In __make_request() a new r10bio is allocated and passed to
raid10_read_request(). The read_slot member of the bio is not
initialized, and the raid10_read_request() uses it to index an
array. This leads to occasional panics.

Fix by initializing the field to invalid value and checking for
valid value in raid10_read_request().

Cc: stable@vger.kernel.org
Signed-off-by: Kevin Vigor <kvigor@gmail.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index d08d77b9674fffdf875f244faf30e31c95337224..419ecdd914f4cff14bb81a36fa226a9b0f1e3ed2 100644 (file)
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1120,7 +1120,7 @@ static void raid10_read_request(struct mddev *mddev, struct bio *bio,
        struct md_rdev *err_rdev = NULL;
        gfp_t gfp = GFP_NOIO;
 
-       if (r10_bio->devs[slot].rdev) {
+       if (slot >= 0 && r10_bio->devs[slot].rdev) {
                /*
                 * This is an error retry, but we cannot
                 * safely dereference the rdev in the r10_bio,
@@ -1513,6 +1513,7 @@ static void __make_request(struct mddev *mddev, struct bio *bio, int sectors)
        r10_bio->mddev = mddev;
        r10_bio->sector = bio->bi_iter.bi_sector;
        r10_bio->state = 0;
+       r10_bio->read_slot = -1;
        memset(r10_bio->devs, 0, sizeof(r10_bio->devs[0]) * conf->copies);
 
        if (bio_data_dir(bio) == READ)