[PATCH 4.19 08/50] ovl: skip getxattr of security labels

From: Greg Kroah-Hartman
Date: Mon Feb 22 2021 - 07:44:02 EST


From: Amir Goldstein <amir73il@xxxxxxxxx>

[ 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@xxxxxxxxx>
Tested-by: Michael Labriola <michael.d.labriola@xxxxxxxxx>
Link: https://lore.kernel.org/linux-unionfs/2nv9d47zt7.fsf@xxxxxxxxxxxxxxxxxxxxxxxxx/
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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 6eb0b882ad231..e164f489d01d9 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -79,6 +79,14 @@ 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)
@@ -102,13 +110,6 @@ retry:
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