linux-kernel - [RFC PATCH 5/8] sg_new_write(): don't bother with access

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Date:   Thu, 17 Oct 2019 20:39:22 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     linux-scsi@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>
Subject: [RFC PATCH 5/8] sg_new_write(): don't bother with access_ok

From: Al Viro <viro@...iv.linux.org.uk>

... just use copy_from_user().  We copy only SZ_SG_IO_HDR bytes,
so that would, strictly speaking, loosen the check.  However,
for call chains via ->write() the caller has actually checked
the entire range and SG_IO passes exactly SZ_SG_IO_HDR for count.
So no visible behaviour changes happen if we check only what
we really need for copyin.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 drivers/scsi/sg.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 2d30e89075e9..3702f66493f7 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -717,8 +717,6 @@ sg_new_write(Sg_fd *sfp, struct file *file, const char __user *buf,
 
 	if (count < SZ_SG_IO_HDR)
 		return -EINVAL;
-	if (!access_ok(buf, count))
-		return -EFAULT; /* protects following copy_from_user()s + get_user()s */
 
 	sfp->cmd_q = 1;	/* when sg_io_hdr seen, set command queuing on */
 	if (!(srp = sg_add_request(sfp))) {
@@ -728,7 +726,7 @@ sg_new_write(Sg_fd *sfp, struct file *file, const char __user *buf,
 	}
 	srp->sg_io_owned = sg_io_owned;
 	hp = &srp->header;
-	if (__copy_from_user(hp, buf, SZ_SG_IO_HDR)) {
+	if (copy_from_user(hp, buf, SZ_SG_IO_HDR)) {
 		sg_remove_request(sfp, srp);
 		return -EFAULT;
 	}
-- 
2.11.0