bcache: fix overflow in offset_to_stripe()

offset_to_stripe() returns the stripe number (in type unsigned int) from
an offset (in type uint64_t) by the following calculation,
	do_div(offset, d->stripe_size);
For large capacity backing device (e.g. 18TB) with small stripe size
(e.g. 4KB), the result is 4831838208 and exceeds UINT_MAX. The actual
returned value which caller receives is 536870912, due to the overflow.

Indeed in bcache_device_init(), bcache_device->nr_stripes is limited in
range [1, INT_MAX]. Therefore all valid stripe numbers in bcache are
in range [0, bcache_dev->nr_stripes - 1].

This patch adds a upper limition check in offset_to_stripe(): the max
valid stripe number should be less than bcache_device->nr_stripes. If
the calculated stripe number from do_div() is equal to or larger than
bcache_device->nr_stripe, -EINVAL will be returned. (Normally nr_stripes
is less than INT_MAX, exceeding upper limitation doesn't mean overflow,
therefore -EOVERFLOW is not used as error code.)

This patch also changes nr_stripes' type of struct bcache_device from
'unsigned int' to 'int', and return value type of offset_to_stripe()
from 'unsigned int' to 'int', to match their exact data ranges.

All locations where bcache_device->nr_stripes and offset_to_stripe() are
referenced also get updated for the above type change.

Reported-and-tested-by: Ken Raeburn <raeburn@redhat.com>
Signed-off-by: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org
Link: https://bugzilla.redhat.com/show_bug.cgi?id=1783075
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 3c708e8..2d1743c 100644 (file)
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -264,7 +264,7 @@ struct bcache_device {
 #define BCACHE_DEV_UNLINK_DONE         2
 #define BCACHE_DEV_WB_RUNNING          3
 #define BCACHE_DEV_RATE_DW_RUNNING     4
-       unsigned int            nr_stripes;
+       int                     nr_stripes;
        unsigned int            stripe_size;
        atomic_t                *stripe_sectors_dirty;
        unsigned long           *full_dirty_stripes;

diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 5397a2c..4f4ad6b 100644 (file)
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -521,15 +521,19 @@ void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned int inode,
                                  uint64_t offset, int nr_sectors)
 {
        struct bcache_device *d = c->devices[inode];
-       unsigned int stripe_offset, stripe, sectors_dirty;
+       unsigned int stripe_offset, sectors_dirty;
+       int stripe;
 
        if (!d)
                return;
 
+       stripe = offset_to_stripe(d, offset);
+       if (stripe < 0)
+               return;
+
        if (UUID_FLASH_ONLY(&c->uuids[inode]))
                atomic_long_add(nr_sectors, &c->flash_dev_dirty_sectors);
 
-       stripe = offset_to_stripe(d, offset);
        stripe_offset = offset & (d->stripe_size - 1);
 
        while (nr_sectors) {
@@ -569,12 +573,12 @@ static bool dirty_pred(struct keybuf *buf, struct bkey *k)
 static void refill_full_stripes(struct cached_dev *dc)
 {
        struct keybuf *buf = &dc->writeback_keys;
-       unsigned int start_stripe, stripe, next_stripe;
+       unsigned int start_stripe, next_stripe;
+       int stripe;
        bool wrapped = false;
 
        stripe = offset_to_stripe(&dc->disk, KEY_OFFSET(&buf->last_scanned));
-
-       if (stripe >= dc->disk.nr_stripes)
+       if (stripe < 0)
                stripe = 0;
 
        start_stripe = stripe;

diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h
index b029843..3f1230e 100644 (file)
--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -52,10 +52,22 @@ static inline uint64_t bcache_dev_sectors_dirty(struct bcache_device *d)
        return ret;
 }
 
-static inline unsigned int offset_to_stripe(struct bcache_device *d,
+static inline int offset_to_stripe(struct bcache_device *d,
                                        uint64_t offset)
 {
        do_div(offset, d->stripe_size);
+
+       /* d->nr_stripes is in range [1, INT_MAX] */
+       if (unlikely(offset >= d->nr_stripes)) {
+               pr_err("Invalid stripe %llu (>= nr_stripes %d).\n",
+                       offset, d->nr_stripes);
+               return -EINVAL;
+       }
+
+       /*
+        * Here offset is definitly smaller than INT_MAX,
+        * return it as int will never overflow.
+        */
        return offset;
 }
 
@@ -63,7 +75,10 @@ static inline bool bcache_dev_stripe_dirty(struct cached_dev *dc,
                                           uint64_t offset,
                                           unsigned int nr_sectors)
 {
-       unsigned int stripe = offset_to_stripe(&dc->disk, offset);
+       int stripe = offset_to_stripe(&dc->disk, offset);
+
+       if (stripe < 0)
+               return false;
 
        while (1) {
                if (atomic_read(dc->disk.stripe_sectors_dirty + stripe))