This is a note to let you know that I've just added the patch titled
btrfs: check if root is readonly while setting security xattr
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-check-if-root-is-readonly-while-setting-security-xattr.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From b51111271b0352aa596c5ae8faf06939e91b3b68 Mon Sep 17 00:00:00 2001
From: Goldwyn Rodrigues <rgoldwyn@xxxxxxx>
Date: Tue, 16 Aug 2022 16:42:56 -0500
Subject: btrfs: check if root is readonly while setting security xattr
From: Goldwyn Rodrigues <rgoldwyn@xxxxxxx>
commit b51111271b0352aa596c5ae8faf06939e91b3b68 upstream.
For a filesystem which has btrfs read-only property set to true, all
write operations including xattr should be denied. However, security
xattr can still be changed even if btrfs ro property is true.
This happens because xattr_permission() does not have any restrictions
on security.*, system.* and in some cases trusted.* from VFS and
the decision is left to the underlying filesystem. See comments in
xattr_permission() for more details.
This patch checks if the root is read-only before performing the set
xattr operation.
Testcase:
DEV=/dev/vdb
MNT=/mnt
mkfs.btrfs -f $DEV
mount $DEV $MNT
echo "file one" > $MNT/f1
setfattr -n "security.one" -v 2 $MNT/f1
btrfs property set /mnt ro true
setfattr -n "security.one" -v 1 $MNT/f1
umount $MNT
CC: stable@xxxxxxxxxxxxxxx # 4.9+
Reviewed-by: Qu Wenruo <wqu@xxxxxxxx>
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/xattr.c | 3 +++
1 file changed, 3 insertions(+)
--- a/fs/btrfs/xattr.c
+++ b/fs/btrfs/xattr.c
@@ -375,6 +375,9 @@ static int btrfs_xattr_handler_get(const
struct dentry *unused, struct inode *inode,
const char *name, void *buffer, size_t size)
{
+ if (btrfs_root_readonly(BTRFS_I(inode)->root))
+ return -EROFS;
+
name = xattr_full_name(handler, name);
return __btrfs_getxattr(inode, name, buffer, size);
}
Patches currently in stable-queue which might be from rgoldwyn@xxxxxxx are
queue-4.9/btrfs-check-if-root-is-readonly-while-setting-security-xattr.patch
