** Tags added: patch
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https://bugs.launchpad.net/bugs/2009065
Title:
overlayfs mounts as R/O over idmapped mount
Status in linux package in Ubuntu:
Incomplete
Bug description:
Reproducer:
create unprivileged LXC container
$ lxc launch ubuntu:22.04 idmap-test
$ lxc exec idmap-test bash
check that root is idmapped by:
$ cat /proc/self/mountinfo | grep idmap
780 675 8:1 /var/snap/lxd/common/lxd/storage-
pools/default/containers/idmap-test/rootfs / rw,relatime,idmapped
shared:323 master:319 - ext4 /dev/sda1 rw,discard,errors=remount-ro
$ mkdir {work,upper,lower,ovl}
$ mount -t overlay overlay -o lowerdir=lower,upperdir=upper,workdir=work ovl
$ touch ovl/test
touch: cannot touch 'ovl/test': Read-only file system
The problem is in __vfs_removexattr_noperm() function that called from
ovl_workdir_create().
In dmesg I can see an error:
overlayfs: failed to create directory work/work (errno: 1); mounting read-only
Reproducible on:
# uname -a
Linux ubuntu 5.19.0-32-generic #33~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Mon Jan
30 17:03:34 UTC 2 x86_64 x86_64 x86_64 GNU/Linux
# cat /etc/os-release
PRETTY_NAME="Ubuntu 22.04.1 LTS"
Suspicious commit:
https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/jammy/commit/fs/overlayfs/overlayfs.h?h=Ubuntu-hwe-5.19-5.19.0-32.33_22.04.1&id=3418435738af5730918fafbdfe2905a98ce2ef05
Chunk:
+ inode_lock(inode);
+ err = __vfs_setxattr_noperm(&init_user_ns, dentry, name, value, size,
flags);
+ inode_unlock(inode);
should be:
+ inode_lock(inode);
+ err = __vfs_setxattr_noperm(ovl_upper_mnt_userns(ofs), dentry, name,
value, size, flags);
+ inode_unlock(inode);
I'll send a patch soon.
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