[PATCH] lib/iov_iter: fix bvec iterator setup

[PATCH] lib/iov_iter: fix bvec iterator setup

[Ming Lei]

.bi_size of bvec iterator should be initialized as real max size for
walking, and .bi_bvec_done just counts how many bytes need to be
skipped in the 1st bvec, so .bi_size isn't related with .bi_bvec_done.

This patch fixes bvec iterator initialization, and the inner `size`
check isn't needed any more, so revert Eric Dumazet's commit
7bc802acf193 ("iov-iter: do not return more bytes than requested in
iov_iter_extract_bvec_pages()").

Cc: Eric Dumazet <edumazet@google.com>
Fixes: e4e535bff2bc ("iov_iter: don't require contiguous pages in iov_iter_extract_bvec_pages")
Reported-by: syzbot+71abe7ab2b70bca770fd@syzkaller.appspotmail.com
Tested-by: syzbot+71abe7ab2b70bca770fd@syzkaller.appspotmail.com
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
Hi Jens,

If possible, please merge this one with Eric's commit.


 lib/iov_iter.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 3026bdcb4738..4a54c7af62c0 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1700,7 +1700,7 @@ static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,
 		skip = 0;
 	}
 	bi.bi_idx = 0;
-	bi.bi_size = maxsize + skip;
+	bi.bi_size = maxsize;
 	bi.bi_bvec_done = skip;
 
 	maxpages = want_pages_array(pages, maxsize, skip, maxpages);
@@ -1724,10 +1724,6 @@ static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,
 		(*pages)[k++] = bv.bv_page;
 		size += bv.bv_len;
 
-		if (size >= maxsize) {
-			size = maxsize;
-			break;
-		}
 		if (k >= maxpages)
 			break;
 
-- 
2.46.0

Re: [PATCH] lib/iov_iter: fix bvec iterator setup

[Jens Axboe]

On 11/1/24 7:42 PM, Ming Lei wrote:
> .bi_size of bvec iterator should be initialized as real max size for
> walking, and .bi_bvec_done just counts how many bytes need to be
> skipped in the 1st bvec, so .bi_size isn't related with .bi_bvec_done.
> 
> This patch fixes bvec iterator initialization, and the inner `size`
> check isn't needed any more, so revert Eric Dumazet's commit
> 7bc802acf193 ("iov-iter: do not return more bytes than requested in
> iov_iter_extract_bvec_pages()").
> 
> Cc: Eric Dumazet <edumazet@google.com>
> Fixes: e4e535bff2bc ("iov_iter: don't require contiguous pages in iov_iter_extract_bvec_pages")
> Reported-by: syzbot+71abe7ab2b70bca770fd@syzkaller.appspotmail.com
> Tested-by: syzbot+71abe7ab2b70bca770fd@syzkaller.appspotmail.com
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> Hi Jens,
> 
> If possible, please merge this one with Eric's commit.

I can just swap them out.

-- 
Jens Axboe