[PATCH 5.7 060/204] bcache: fix overflow in offset_to_stripe()

Greg Kroah-Hartman
2020-08-20T13:06:18Z

From: Coly Li <colyli@suse.de>

commit 7a1481267999c02abf4a624515c1b5c7c1fccbd6 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/md/bcache/bcache.h | 2 +-
drivers/md/bcache/writeback.c | 14 +++++++++-----
drivers/md/bcache/writeback.h | 19 +++++++++++++++++--
3 files changed, 27 insertions(+), 8 deletions(-)

--- 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;
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -523,15 +523,19 @@ void bcache_dev_sectors_dirty_add(struct
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) {
@@ -571,12 +575,12 @@ static bool dirty_pred(struct keybuf *bu
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;
--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -52,10 +52,22 @@ static inline uint64_t bcache_dev_sector
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_dir
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))