[PATCH v2 3/3] io_uring: don't assume uaddr alignment in io_vec_fill_bvec

[Pavel Begunkov <asml.silence@gmail.com>]

There is no guaranteed alignment for user pointers. Don't use mask
trickery and adjust the offset by bv_offset.

Cc: stable@vger.kernel.org
Reported-by: David Hildenbrand <david@redhat.com>
Fixes: 9ef4cbbcb4ac3 ("io_uring: add infra for importing vectored reg buffers")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/rsrc.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 8b06c732d136..c58fe736f297 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -1336,7 +1336,6 @@ static int io_vec_fill_bvec(int ddir, struct iov_iter *iter,
 {
 	unsigned long folio_size = 1 << imu->folio_shift;
 	unsigned long folio_mask = folio_size - 1;
-	u64 folio_addr = imu->ubuf & ~folio_mask;
 	struct bio_vec *res_bvec = vec->bvec;
 	size_t total_len = 0;
 	unsigned bvec_idx = 0;
@@ -1358,8 +1357,13 @@ static int io_vec_fill_bvec(int ddir, struct iov_iter *iter,
 		if (unlikely(check_add_overflow(total_len, iov_len, &total_len)))
 			return -EOVERFLOW;
 
-		/* by using folio address it also accounts for bvec offset */
-		offset = buf_addr - folio_addr;
+		offset = buf_addr - imu->ubuf;
+		/*
+		 * Only the first bvec can have non zero bv_offset, account it
+		 * here and work with full folios below.
+		 */
+		offset += imu->bvec[0].bv_offset;
+
 		src_bvec = imu->bvec + (offset >> imu->folio_shift);
 		offset &= folio_mask;
 
-- 
2.49.0