Re: [PATCH] block: bio: Trim bio to sensible size in bio_trim()

Re: [PATCH] block: bio: Trim bio to sensible size in bio_trim()

[linmiaohe]

Jens Axboe <axboe@kernel.dk> wrote:
>On 8/29/20 3:37 AM, Miaohe Lin wrote:
>> Trim bio to sensible size in bio_trim() or something bad may happen.
>
>This really needs a LOT more detail. What is "something bad"? How does this condition trigger to begin with?
>

Many thanks for your reply.

I do this mainly by code review, so I didn't find the condition trigger to begin with. But I think it's better
to do such a check as this is a external Interface. Also If bio_trim() set bio->bi_iter.bi_size to a value larger than the origin one,
we may access the bio_vec past the last one of bio->bi_io_vec in for_each_bvec macro.

>--
>Jens Axboe
>

Re: [PATCH] block: bio: Trim bio to sensible size in bio_trim()

[Jens Axboe]

On 8/29/20 3:37 AM, Miaohe Lin wrote:
> Trim bio to sensible size in bio_trim() or something bad may happen.

This really needs a LOT more detail. What is "something bad"? How does
this condition trigger to begin with?

-- 
Jens Axboe

[PATCH] block: bio: Trim bio to sensible size in bio_trim()

[Miaohe Lin]

Trim bio to sensible size in bio_trim() or something bad may happen.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 block/bio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index a9931f23d933..94e4f97d3d4e 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1509,7 +1509,8 @@ void bio_trim(struct bio *bio, int offset, int size)
 		return;
 
 	bio_advance(bio, offset << 9);
-	bio->bi_iter.bi_size = size;
+	if (likely(bio->bi_iter.bi_size >= size))
+		bio->bi_iter.bi_size = size;
 
 	if (bio_integrity(bio))
 		bio_integrity_trim(bio);
-- 
2.19.1