linux-kernel - [PATCH AUTOSEL 4.9 2/4] ovl: skip getxattr of security labels

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Message-Id: <20210208180000.2092497-2-sashal@kernel.org>
Date:   Mon,  8 Feb 2021 12:59:58 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Amir Goldstein <amir73il@...il.com>,
        Michael Labriola <michael.d.labriola@...il.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Sasha Levin <sashal@...nel.org>, linux-unionfs@...r.kernel.org
Subject: [PATCH AUTOSEL 4.9 2/4] ovl: skip getxattr of security labels

From: Amir Goldstein <amir73il@...il.com>

[ Upstream commit 03fedf93593c82538b18476d8c4f0e8f8435ea70 ]

When inode has no listxattr op of its own (e.g. squashfs) vfs_listxattr
calls the LSM inode_listsecurity hooks to list the xattrs that LSMs will
intercept in inode_getxattr hooks.

When selinux LSM is installed but not initialized, it will list the
security.selinux xattr in inode_listsecurity, but will not intercept it
in inode_getxattr.  This results in -ENODATA for a getxattr call for an
xattr returned by listxattr.

This situation was manifested as overlayfs failure to copy up lower
files from squashfs when selinux is built-in but not initialized,
because ovl_copy_xattr() iterates the lower inode xattrs by
vfs_listxattr() and vfs_getxattr().

ovl_copy_xattr() skips copy up of security labels that are indentified by
inode_copy_up_xattr LSM hooks, but it does that after vfs_getxattr().
Since we are not going to copy them, skip vfs_getxattr() of the security
labels.

Reported-by: Michael Labriola <michael.d.labriola@...il.com>
Tested-by: Michael Labriola <michael.d.labriola@...il.com>
Link: https://lore.kernel.org/linux-unionfs/2nv9d47zt7.fsf@aldarion.sourceruckus.org/
Signed-off-by: Amir Goldstein <amir73il@...il.com>
Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/overlayfs/copy_up.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 299dbf59f28f8..3a583aa1fafeb 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -92,6 +92,14 @@ int ovl_copy_xattr(struct dentry *old, struct dentry *new)

 		if (ovl_is_private_xattr(name))
 			continue;
+
+		error = security_inode_copy_up_xattr(name);
+		if (error < 0 && error != -EOPNOTSUPP)
+			break;
+		if (error == 1) {
+			error = 0;
+			continue; /* Discard */
+		}
 retry:
 		size = vfs_getxattr(old, name, value, value_size);
 		if (size == -ERANGE)
@@ -115,13 +123,6 @@ int ovl_copy_xattr(struct dentry *old, struct dentry *new)
 			goto retry;
 		}

-		error = security_inode_copy_up_xattr(name);
-		if (error < 0 && error != -EOPNOTSUPP)
-			break;
-		if (error == 1) {
-			error = 0;
-			continue; /* Discard */
-		}
 		error = vfs_setxattr(new, name, value, size, 0);
 		if (error)
 			break;
-- 
2.27.0