block-map: add __GFP_ZERO flag for alloc_page in function bio_copy_kern

Add __GFP_ZERO flag for alloc_page in function bio_copy_kern to initialize the buffer of a bio.

---
This can cause a kernel-info-leak problem.
0. This problem occurred in function scsi_ioctl. If the parameter cmd is SCSI_IOCTL_SEND_COMMAND, the function scsi_ioctl will call sg_scsi_ioctl to further process.
1. In function sg_scsi_ioctl, it creates a scsi request and calls blk_rq_map_kern to map kernel data to a request.
3. blq_rq_map_kern calls bio_copy_kern to request a bio.
4. bio_copy_kern calls alloc_page to request the buffer of a bio. In the case of reading, it wouldn't fill anything into the buffer.

```
__alloc_pages+0xbbf/0x1090 build/../mm/page_alloc.c:5409
alloc_pages+0x8a5/0xb80
bio_copy_kern build/../block/blk-map.c:449 [inline]
blk_rq_map_kern+0x813/0x1400 build/../block/blk-map.c:640
sg_scsi_ioctl build/../drivers/scsi/scsi_ioctl.c:618 [inline]
scsi_ioctl+0x40c0/0x4600 build/../drivers/scsi/scsi_ioctl.c:932
sg_ioctl_common build/../drivers/scsi/sg.c:1112 [inline]
sg_ioctl+0x3351/0x4c10 build/../drivers/scsi/sg.c:1165
vfs_ioctl build/../fs/ioctl.c:51 [inline]
__do_sys_ioctl build/../fs/ioctl.c:874 [inline]
__se_sys_ioctl+0x2df/0x4a0 build/../fs/ioctl.c:860
__x64_sys_ioctl+0xd8/0x110 build/../fs/ioctl.c:860
do_syscall_x64 build/../arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x54/0xd0 build/../arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x44/0xae
```

5. Then this request will be sent to the disk driver. When bio is finished, bio_copy_kern_endio_read will copy the readed content back to parameter data from the bio. But if the block driver didn't process this request, the buffer of bio is still unitialized.

```
memcpy_from_page build/../include/linux/highmem.h:346 [inline]
memcpy_from_bvec build/../include/linux/bvec.h:207 [inline]
bio_copy_kern_endio_read+0x4a3/0x620 build/../block/blk-map.c:403
bio_endio+0xa7f/0xac0 build/../block/bio.c:1491
req_bio_endio build/../block/blk-mq.c:674 [inline]
blk_update_request+0x1129/0x22d0 build/../block/blk-mq.c:742
scsi_end_request+0x119/0xe40 build/../drivers/scsi/scsi_lib.c:543
scsi_io_completion+0x329/0x810 build/../drivers/scsi/scsi_lib.c:939
scsi_finish_command+0x6e3/0x700 build/../drivers/scsi/scsi.c:199
scsi_complete+0x239/0x640 build/../drivers/scsi/scsi_lib.c:1441
blk_complete_reqs build/../block/blk-mq.c:892 [inline]
blk_done_softirq+0x189/0x260 build/../block/blk-mq.c:897
__do_softirq+0x1ee/0x7c5 build/../kernel/softirq.c:558
```

6. Finally, the internal buffer's content is copied to the user buffer which is specified by the parameter sic->data of sg_scsi_ioctl.

_copy_to_user+0x1c9/0x270 build/../lib/usercopy.c:33
copy_to_user build/../include/linux/uaccess.h:209 [inline]
sg_scsi_ioctl build/../drivers/scsi/scsi_ioctl.c:634 [inline]
scsi_ioctl+0x44d9/0x4600 build/../drivers/scsi/scsi_ioctl.c:932
sg_ioctl_common build/../drivers/scsi/sg.c:1112 [inline]
sg_ioctl+0x3351/0x4c10 build/../drivers/scsi/sg.c:1165
vfs_ioctl build/../fs/ioctl.c:51 [inline]
__do_sys_ioctl build/../fs/ioctl.c:874 [inline]
__se_sys_ioctl+0x2df/0x4a0 build/../fs/ioctl.c:860
__x64_sys_ioctl+0xd8/0x110 build/../fs/ioctl.c:860
do_syscall_x64 build/../arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x54/0xd0 build/../arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x44/0xae
 block/blk-map.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 4526adde0156..c7f71d83eff1 100644
@@ -446,7 +446,7 @@ static struct bio *bio_copy_kern(struct request_queue *q, void *data,
 		if (bytes > len)
 			bytes = len;
 
-		page = alloc_page(GFP_NOIO | gfp_mask);
+		page = alloc_page(GFP_NOIO | __GFP_ZERO | gfp_mask);
 		if (!page)
 			goto cleanup;
 

2.30.1 (Apple Git-130)

but blk_rq_map_kern() does accept gfp_mask for exactly this same case and that is passed on to the bio_copy_kern() unless I'm wrong here, so you need to pass the __GFP_ZERO flag in the step 3 above (sg_scsi_ioctl) and not force zzeroed allocation the generic API..

-ck

no top posting

and there is a way to fix it by passing the right gfp flag for scsi case why modify core code ? in absence of flag I can understand but that is not the case ...

-ck

We only want the zeroing for the payload, and other callers have the same issue, so I think this patch is the right thing to do.

okay, in that case looks good...

Looks good:

Applied, thanks!

[1/1] block-map: add __GFP_ZERO flag for alloc_page in function bio_copy_kern
(no commit info)

Best regards,

Jens Axboe