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From: Kees Cook <keescook@chromium.org>
Subject: [PATCH 09/36] vfs: Copy struct mount.mnt_id to userspace using put_user()
Date: Tue,  9 Jan 2018 12:55:38 -0800
Message-Id: <1515531365-37423-10-git-send-email-keescook@chromium.org>
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To: linux-kernel@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>, David Windsor <dave@nullcore.net>, Alexander Viro <viro@zeniv.linux.org.uk>, linux-fsdevel@vger.kernel.org, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, Andy Lutomirski <luto@kernel.org>, Christoph Hellwig <hch@infradead.org>, Christoph Lameter <cl@linux.com>, "David S. Miller" <davem@davemloft.net>, Laura Abbott <labbott@redhat.com>, Mark Rutland <mark.rutland@arm.com>, "Martin K. Petersen" <martin.petersen@oracle.com>, Paolo Bonzini <pbonzini@redhat.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Christoffer Dall <christoffer.dall@linaro.org>, Dave Kleikamp <dave.kleikamp@oracle.com>, Jan Kara <jack@suse.cz>, Luis de Bethencourt <luisbg@kernel.org>, Marc Zyngier <marc.zyngier@arm.com>, Rik van Riel <riel@redhat.com>, Matthew Garrett <mjg59@google.com>, linux-arch@vger.kernel.org, netdev@vger.kernel.org, linux-mm@kvack.org, kernel-hardening@lists.openwall.com

From: David Windsor <dave@nullcore.net>

The mnt_id field can be copied with put_user(), so there is no need to
use copy_to_user(). In both cases, hardened usercopy is being bypassed
since the size is constant, and not open to runtime manipulation.

This patch is verbatim from Brad Spengler/PaX Team's PAX_USERCOPY
whitelisting code in the last public patch of grsecurity/PaX based on my
understanding of the code. Changes or omissions from the original code are
mine and don't reflect the original grsecurity/PaX code.

Signed-off-by: David Windsor <dave@nullcore.net>
[kees: adjust commit log]
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 fs/fhandle.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/fhandle.c b/fs/fhandle.c
index 0ace128f5d23..0ee727485615 100644
--- a/fs/fhandle.c
+++ b/fs/fhandle.c
@@ -69,8 +69,7 @@ static long do_sys_name_to_handle(struct path *path,
 	} else
 		retval = 0;
 	/* copy the mount id */
-	if (copy_to_user(mnt_id, &real_mount(path->mnt)->mnt_id,
-			 sizeof(*mnt_id)) ||
+	if (put_user(real_mount(path->mnt)->mnt_id, mnt_id) ||
 	    copy_to_user(ufh, handle,
 			 sizeof(struct file_handle) + handle_bytes))
 		retval = -EFAULT;
-- 
2.7.4

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