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authorKent Overstreet <kent.overstreet@gmail.com>2012-02-08 22:07:18 +0100
committerJens Axboe <axboe@kernel.dk>2012-02-08 22:07:18 +0100
commit5abebfdd02450fa1349daacf242e70b3736581e3 (patch)
tree6dc62283b65c71fc22c643635c773fef42d9a978 /fs/bio.c
parent4609dff6b5d11e1ed5ff935e15f9f6022acb312b (diff)
downloadvexpress-lsk-5abebfdd02450fa1349daacf242e70b3736581e3.tar.gz
bio: don't overflow in bio_get_nr_vecs()
There were two places bio_get_nr_vecs() could overflow: First, it did a left shift to convert from sectors to bytes immediately before dividing by PAGE_SIZE. If PAGE_SIZE ever was less than 512 a great many things would break, so dividing by PAGE_SIZE >> 9 is safe and will generate smaller code too. The nastier overflow was in the DIV_ROUND_UP() (that's what the code was effectively doing, anyways). If n + d overflowed, the whole thing would return 0 which breaks things rather effectively. bio_get_nr_vecs() doesn't claim to give an exact value anyways, so the DIV_ROUND_UP() is silly; we could do a straight divide except if a device's queue_max_sectors was less than PAGE_SIZE we'd return 0. So we just add 1; this should always be safe - things will break badly if bio_get_nr_vecs() returns > BIO_MAX_PAGES (bio_alloc() will suddenly start failing) but it's queue_max_segments that must guard against this, if queue_max_sectors is preventing this from happen things are going to explode on architectures with different PAGE_SIZE. Signed-off-by: Kent Overstreet <koverstreet@google.com> Cc: Tejun Heo <tj@kernel.org> Acked-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'fs/bio.c')
-rw-r--r--fs/bio.c10
1 files changed, 3 insertions, 7 deletions
diff --git a/fs/bio.c b/fs/bio.c
index b1fe82cf88c..b980ecde026 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -505,13 +505,9 @@ EXPORT_SYMBOL(bio_clone);
int bio_get_nr_vecs(struct block_device *bdev)
{
struct request_queue *q = bdev_get_queue(bdev);
- int nr_pages;
-
- nr_pages = ((queue_max_sectors(q) << 9) + PAGE_SIZE - 1) >> PAGE_SHIFT;
- if (nr_pages > queue_max_segments(q))
- nr_pages = queue_max_segments(q);
-
- return nr_pages;
+ return min_t(unsigned,
+ queue_max_segments(q),
+ queue_max_sectors(q) / (PAGE_SIZE >> 9) + 1);
}
EXPORT_SYMBOL(bio_get_nr_vecs);