linux-kernel - [PATCH 1/2] ecryptfs: fix uid translation for setxattr on security.capability

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Message-Id: <20210119162204.2081137-2-mszeredi@redhat.com>
Date:   Tue, 19 Jan 2021 17:22:03 +0100
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     "Eric W . Biederman" <ebiederm@...ssion.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-unionfs@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Tyler Hicks <code@...icks.com>
Subject: [PATCH 1/2] ecryptfs: fix uid translation for setxattr on security.capability

Prior to commit 7c03e2cda4a5 ("vfs: move cap_convert_nscap() call into
vfs_setxattr()") the translation of nscap->rootid did not take stacked
filesystems (overlayfs and ecryptfs) into account.

That patch fixed the overlay case, but made the ecryptfs case worse.

Restore old the behavior for ecryptfs that existed before the overlayfs
fix.  This does not fix ecryptfs's handling of complex user namespace
setups, but it does make sure existing setups don't regress.

Reported-by: Eric W. Biederman <ebiederm@...ssion.com>
Cc: Tyler Hicks <code@...icks.com>
Fixes: 7c03e2cda4a5 ("vfs: move cap_convert_nscap() call into vfs_setxattr()")
Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
---
 fs/ecryptfs/inode.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
index e23752d9a79f..58d0f7187997 100644
--- a/fs/ecryptfs/inode.c
+++ b/fs/ecryptfs/inode.c
@@ -1016,15 +1016,19 @@ ecryptfs_setxattr(struct dentry *dentry, struct inode *inode,
 {
 	int rc;
 	struct dentry *lower_dentry;
+	struct inode *lower_inode;
 
 	lower_dentry = ecryptfs_dentry_to_lower(dentry);
-	if (!(d_inode(lower_dentry)->i_opflags & IOP_XATTR)) {
+	lower_inode = d_inode(lower_dentry);
+	if (!(lower_inode->i_opflags & IOP_XATTR)) {
 		rc = -EOPNOTSUPP;
 		goto out;
 	}
-	rc = vfs_setxattr(lower_dentry, name, value, size, flags);
+	inode_lock(lower_inode);
+	rc = __vfs_setxattr_locked(lower_dentry, name, value, size, flags, NULL);
+	inode_unlock(lower_inode);
 	if (!rc && inode)
-		fsstack_copy_attr_all(inode, d_inode(lower_dentry));
+		fsstack_copy_attr_all(inode, lower_inode);
 out:
 	return rc;
 }
-- 
2.26.2