linux-kernel - [PATCH] floppy: Do not copy a kernel pointer to user memory in FDGETPRM ioctl

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Date:   Wed,  7 Mar 2018 16:02:45 -0800
From:   Brian Belleville <bbellevi@....edu>
To:     Jiri Kosina <jikos@...nel.org>, linux-kernel@...r.kernel.org
Cc:     Brian Belleville <bbellevi@....edu>
Subject: [PATCH] floppy: Do not copy a kernel pointer to user memory in FDGETPRM ioctl

The final field of a floppy_struct is the field "name", which is a
pointer to a string in kernel memory. The kernel pointer should not be
copied to user memory. The FDGETPRM ioctl copies a floppy_struct to
user memory, including the "name" field. This pointer cannot be used
by the user, and it will leak a kernel address to user-space, which
will reveal the location of kernel code and data and undermine KASLR
protection. Instead, copy the floppy_struct except for the "name"
field.

Signed-off-by: Brian Belleville <bbellevi@....edu>
---
 drivers/block/floppy.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index eae484a..4d4a422 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -3470,6 +3470,7 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
 					  (struct floppy_struct **)&outparam);
 		if (ret)
 			return ret;
+		size = offsetof(struct floppy_struct, name);
 		break;
 	case FDMSGON:
 		UDP->flags |= FTD_MSG;
-- 
2.7.4