Re: [PATCH v2] inode: debugfs_create_dir uses mode permission from parent
From: Greg KH
Date: Fri Apr 27 2018 - 09:49:52 EST
I'm going to add Kees and the kernel-hardning list here, as I'd like
their opinions for the patch below.
Kees, do you have any problems with this patch? I know you worked on
making debugfs more "secure" from non-root users, this should still keep
the intial mount permissions all fine, right? Anything I'm not
considering here?
thanks,
greg k-h
On Fri, Apr 27, 2018 at 02:35:47PM +0200, Thomas Richter wrote:
> Currently function debugfs_create_dir() creates a new
> directory in the debugfs (usually mounted /sys/kernel/debug)
> with permission rwxr-xr-x. This is hard coded.
>
> Change this to use the parent directory permission.
>
> Output before the patch:
> root@s8360047 ~]# tree -dp -L 1 /sys/kernel/debug/
> /sys/kernel/debug/
> âââ [drwxr-xr-x] bdi
> âââ [drwxr-xr-x] block
> âââ [drwxr-xr-x] dasd
> âââ [drwxr-xr-x] device_component
> âââ [drwxr-xr-x] extfrag
> âââ [drwxr-xr-x] hid
> âââ [drwxr-xr-x] kprobes
> âââ [drwxr-xr-x] kvm
> âââ [drwxr-xr-x] memblock
> âââ [drwxr-xr-x] pm_qos
> âââ [drwxr-xr-x] qdio
> âââ [drwxr-xr-x] s390
> âââ [drwxr-xr-x] s390dbf
> âââ [drwx------] tracing
>
> 14 directories
> [root@s8360047 linux]#
>
> Output after the patch:
> [root@s8360047 ~]# tree -dp -L 1 /sys/kernel/debug/
> sys/kernel/debug/
> âââ [drwx------] bdi
> âââ [drwx------] block
> âââ [drwx------] dasd
> âââ [drwx------] device_component
> âââ [drwx------] extfrag
> âââ [drwx------] hid
> âââ [drwx------] kprobes
> âââ [drwx------] kvm
> âââ [drwx------] memblock
> âââ [drwx------] pm_qos
> âââ [drwx------] qdio
> âââ [drwx------] s390
> âââ [drwx------] s390dbf
> âââ [drwx------] tracing
>
> 14 directories
> [root@s8360047 linux]#
>
> Here is the full diff output done with:
> [root@s8360047 ~]# diff -u treefull.before treefull.after |
> sed 's-^- # -' > treefull.diff
> # --- treefull.before 2018-04-27 13:22:04.532824564 +0200
> # +++ treefull.after 2018-04-27 13:24:12.106182062 +0200
> # @@ -1,55 +1,55 @@
> # /sys/kernel/debug/
> # -âââ [drwxr-xr-x] bdi
> # -â âââ [drwxr-xr-x] 1:0
> # -â âââ [drwxr-xr-x] 1:1
> # -â âââ [drwxr-xr-x] 1:10
> # -â âââ [drwxr-xr-x] 1:11
> # -â âââ [drwxr-xr-x] 1:12
> # -â âââ [drwxr-xr-x] 1:13
> # -â âââ [drwxr-xr-x] 1:14
> # -â âââ [drwxr-xr-x] 1:15
> # -â âââ [drwxr-xr-x] 1:2
> # -â âââ [drwxr-xr-x] 1:3
> # -â âââ [drwxr-xr-x] 1:4
> # -â âââ [drwxr-xr-x] 1:5
> # -â âââ [drwxr-xr-x] 1:6
> # -â âââ [drwxr-xr-x] 1:7
> # -â âââ [drwxr-xr-x] 1:8
> # -â âââ [drwxr-xr-x] 1:9
> # -â âââ [drwxr-xr-x] 94:0
> # -âââ [drwxr-xr-x] block
> # -âââ [drwxr-xr-x] dasd
> # -â âââ [drwxr-xr-x] 0.0.e18a
> # -â âââ [drwxr-xr-x] dasda
> # -â âââ [drwxr-xr-x] global
> # -âââ [drwxr-xr-x] device_component
> # -âââ [drwxr-xr-x] extfrag
> # -âââ [drwxr-xr-x] hid
> # -âââ [drwxr-xr-x] kprobes
> # -âââ [drwxr-xr-x] kvm
> # -âââ [drwxr-xr-x] memblock
> # -âââ [drwxr-xr-x] pm_qos
> # -âââ [drwxr-xr-x] qdio
> # -â âââ [drwxr-xr-x] 0.0.f5f2
> # -âââ [drwxr-xr-x] s390
> # -â âââ [drwxr-xr-x] stsi
> # -âââ [drwxr-xr-x] s390dbf
> # -â âââ [drwxr-xr-x] 0.0.e18a
> # -â âââ [drwxr-xr-x] cio_crw
> # -â âââ [drwxr-xr-x] cio_msg
> # -â âââ [drwxr-xr-x] cio_trace
> # -â âââ [drwxr-xr-x] dasd
> # -â âââ [drwxr-xr-x] kvm-trace
> # -â âââ [drwxr-xr-x] lgr
> # -â âââ [drwxr-xr-x] qdio_0.0.f5f2
> # -â âââ [drwxr-xr-x] qdio_error
> # -â âââ [drwxr-xr-x] qdio_setup
> # -â âââ [drwxr-xr-x] qeth_card_0.0.f5f0
> # -â âââ [drwxr-xr-x] qeth_control
> # -â âââ [drwxr-xr-x] qeth_msg
> # -â âââ [drwxr-xr-x] qeth_setup
> # -â âââ [drwxr-xr-x] vmcp
> # -â âââ [drwxr-xr-x] vmur
> # +âââ [drwx------] bdi
> # +â âââ [drwx------] 1:0
> # +â âââ [drwx------] 1:1
> # +â âââ [drwx------] 1:10
> # +â âââ [drwx------] 1:11
> # +â âââ [drwx------] 1:12
> # +â âââ [drwx------] 1:13
> # +â âââ [drwx------] 1:14
> # +â âââ [drwx------] 1:15
> # +â âââ [drwx------] 1:2
> # +â âââ [drwx------] 1:3
> # +â âââ [drwx------] 1:4
> # +â âââ [drwx------] 1:5
> # +â âââ [drwx------] 1:6
> # +â âââ [drwx------] 1:7
> # +â âââ [drwx------] 1:8
> # +â âââ [drwx------] 1:9
> # +â âââ [drwx------] 94:0
> # +âââ [drwx------] block
> # +âââ [drwx------] dasd
> # +â âââ [drwx------] 0.0.e18a
> # +â âââ [drwx------] dasda
> # +â âââ [drwx------] global
> # +âââ [drwx------] device_component
> # +âââ [drwx------] extfrag
> # +âââ [drwx------] hid
> # +âââ [drwx------] kprobes
> # +âââ [drwx------] kvm
> # +âââ [drwx------] memblock
> # +âââ [drwx------] pm_qos
> # +âââ [drwx------] qdio
> # +â âââ [drwx------] 0.0.f5f2
> # +âââ [drwx------] s390
> # +â âââ [drwx------] stsi
> # +âââ [drwx------] s390dbf
> # +â âââ [drwx------] 0.0.e18a
> # +â âââ [drwx------] cio_crw
> # +â âââ [drwx------] cio_msg
> # +â âââ [drwx------] cio_trace
> # +â âââ [drwx------] dasd
> # +â âââ [drwx------] kvm-trace
> # +â âââ [drwx------] lgr
> # +â âââ [drwx------] qdio_0.0.f5f2
> # +â âââ [drwx------] qdio_error
> # +â âââ [drwx------] qdio_setup
> # +â âââ [drwx------] qeth_card_0.0.f5f0
> # +â âââ [drwx------] qeth_control
> # +â âââ [drwx------] qeth_msg
> # +â âââ [drwx------] qeth_setup
> # +â âââ [drwx------] vmcp
> # +â âââ [drwx------] vmur
> # âââ [drwx------] tracing
> # âââ [drwxr-xr-x] events
> # â âââ [drwxr-xr-x] alarmtimer
>
> Fixes: edac65eaf8d5c ("debugfs: take mode-dependent parts of debugfs_get_inode() into callers")
> Signed-off-by: Thomas Richter <tmricht@xxxxxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
> fs/debugfs/inode.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
> index 13b0135..a913b12 100644
> --- a/fs/debugfs/inode.c
> +++ b/fs/debugfs/inode.c
> @@ -512,7 +512,9 @@ struct dentry *debugfs_create_dir(const char *name, struct dentry *parent)
> if (unlikely(!inode))
> return failed_creating(dentry);
>
> - inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
> + if (!parent)
> + parent = debugfs_mount->mnt_root;
> + inode->i_mode = S_IFDIR | ((d_inode(parent)->i_mode & 0770));
> inode->i_op = &simple_dir_inode_operations;
> inode->i_fop = &simple_dir_operations;
>
> --
> 2.9.3