linux-kernel - [RFC PATCH 7/8] sg_write(): get rid of access_ok()/__copy_from_user()/__get

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Message-Id: <20191017193925.25539-7-viro@ZenIV.linux.org.uk>
Date:   Thu, 17 Oct 2019 20:39:24 +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 7/8] sg_write(): get rid of access_ok()/__copy_from_user()/__get_user()

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

Just use plain copy_from_user() and get_user().  Note that while
a buf-derived pointer gets stored into ->dxferp, all places that
actually use the resulting value feed it either to import_iovec()
or to import_single_range(), and both will do validation.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 drivers/scsi/sg.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 9f6534a025cd..f3d090b93cdf 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -612,11 +612,9 @@ sg_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos)
 	      scsi_block_when_processing_errors(sdp->device)))
 		return -ENXIO;
 
-	if (!access_ok(buf, count))
-		return -EFAULT;	/* protects following copy_from_user()s + get_user()s */
 	if (count < SZ_SG_HEADER)
 		return -EIO;
-	if (__copy_from_user(&old_hdr, buf, SZ_SG_HEADER))
+	if (copy_from_user(&old_hdr, buf, SZ_SG_HEADER))
 		return -EFAULT;
 	blocking = !(filp->f_flags & O_NONBLOCK);
 	if (old_hdr.reply_len < 0)
@@ -626,7 +624,7 @@ sg_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos)
 		return -EIO;	/* The minimum scsi command length is 6 bytes. */
 
 	buf += SZ_SG_HEADER;
-	if (__get_user(opcode, buf))
+	if (get_user(opcode, buf))
 		return -EFAULT;
 
 	if (!(srp = sg_add_request(sfp))) {
@@ -676,7 +674,7 @@ sg_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos)
 	hp->flags = input_size;	/* structure abuse ... */
 	hp->pack_id = old_hdr.pack_id;
 	hp->usr_ptr = NULL;
-	if (__copy_from_user(cmnd, buf, cmd_size))
+	if (copy_from_user(cmnd, buf, cmd_size))
 		return -EFAULT;
 	/*
 	 * SG_DXFER_TO_FROM_DEV is functionally equivalent to SG_DXFER_FROM_DEV,
-- 
2.11.0