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Date: Fri, 27 Apr 2018 15:49:37 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Kees Cook <keescook@...omium.org>,
Thomas Richter <tmricht@...ux.ibm.com>
Cc: kernel-hardening@...ts.openwall.com, brueckner@...ux.vnet.ibm.com,
schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] inode: debugfs_create_dir uses mode permission from
parent
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@...60047 ~]# tree -dp -L 1 /sys/kernel/debug/
> /sys/kernel/debug/
> ├── [drwxr-xr-x] bdi
> ├── [drwxr-xr-x] block
> ├── [drwxr-xr-x] dasd
> ├── [drwxr-xr-x] device_component
> ├── [drwxr-xr-x] extfrag
> ├── [drwxr-xr-x] hid
> ├── [drwxr-xr-x] kprobes
> ├── [drwxr-xr-x] kvm
> ├── [drwxr-xr-x] memblock
> ├── [drwxr-xr-x] pm_qos
> ├── [drwxr-xr-x] qdio
> ├── [drwxr-xr-x] s390
> ├── [drwxr-xr-x] s390dbf
> └── [drwx------] tracing
>
> 14 directories
> [root@...60047 linux]#
>
> Output after the patch:
> [root@...60047 ~]# tree -dp -L 1 /sys/kernel/debug/
> sys/kernel/debug/
> ├── [drwx------] bdi
> ├── [drwx------] block
> ├── [drwx------] dasd
> ├── [drwx------] device_component
> ├── [drwx------] extfrag
> ├── [drwx------] hid
> ├── [drwx------] kprobes
> ├── [drwx------] kvm
> ├── [drwx------] memblock
> ├── [drwx------] pm_qos
> ├── [drwx------] qdio
> ├── [drwx------] s390
> ├── [drwx------] s390dbf
> └── [drwx------] tracing
>
> 14 directories
> [root@...60047 linux]#
>
> Here is the full diff output done with:
> [root@...60047 ~]# 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/
> # -├── [drwxr-xr-x] bdi
> # -│ ├── [drwxr-xr-x] 1:0
> # -│ ├── [drwxr-xr-x] 1:1
> # -│ ├── [drwxr-xr-x] 1:10
> # -│ ├── [drwxr-xr-x] 1:11
> # -│ ├── [drwxr-xr-x] 1:12
> # -│ ├── [drwxr-xr-x] 1:13
> # -│ ├── [drwxr-xr-x] 1:14
> # -│ ├── [drwxr-xr-x] 1:15
> # -│ ├── [drwxr-xr-x] 1:2
> # -│ ├── [drwxr-xr-x] 1:3
> # -│ ├── [drwxr-xr-x] 1:4
> # -│ ├── [drwxr-xr-x] 1:5
> # -│ ├── [drwxr-xr-x] 1:6
> # -│ ├── [drwxr-xr-x] 1:7
> # -│ ├── [drwxr-xr-x] 1:8
> # -│ ├── [drwxr-xr-x] 1:9
> # -│ └── [drwxr-xr-x] 94:0
> # -├── [drwxr-xr-x] block
> # -├── [drwxr-xr-x] dasd
> # -│ ├── [drwxr-xr-x] 0.0.e18a
> # -│ ├── [drwxr-xr-x] dasda
> # -│ └── [drwxr-xr-x] global
> # -├── [drwxr-xr-x] device_component
> # -├── [drwxr-xr-x] extfrag
> # -├── [drwxr-xr-x] hid
> # -├── [drwxr-xr-x] kprobes
> # -├── [drwxr-xr-x] kvm
> # -├── [drwxr-xr-x] memblock
> # -├── [drwxr-xr-x] pm_qos
> # -├── [drwxr-xr-x] qdio
> # -│ └── [drwxr-xr-x] 0.0.f5f2
> # -├── [drwxr-xr-x] s390
> # -│ └── [drwxr-xr-x] stsi
> # -├── [drwxr-xr-x] s390dbf
> # -│ ├── [drwxr-xr-x] 0.0.e18a
> # -│ ├── [drwxr-xr-x] cio_crw
> # -│ ├── [drwxr-xr-x] cio_msg
> # -│ ├── [drwxr-xr-x] cio_trace
> # -│ ├── [drwxr-xr-x] dasd
> # -│ ├── [drwxr-xr-x] kvm-trace
> # -│ ├── [drwxr-xr-x] lgr
> # -│ ├── [drwxr-xr-x] qdio_0.0.f5f2
> # -│ ├── [drwxr-xr-x] qdio_error
> # -│ ├── [drwxr-xr-x] qdio_setup
> # -│ ├── [drwxr-xr-x] qeth_card_0.0.f5f0
> # -│ ├── [drwxr-xr-x] qeth_control
> # -│ ├── [drwxr-xr-x] qeth_msg
> # -│ ├── [drwxr-xr-x] qeth_setup
> # -│ ├── [drwxr-xr-x] vmcp
> # -│ └── [drwxr-xr-x] vmur
> # +├── [drwx------] bdi
> # +│ ├── [drwx------] 1:0
> # +│ ├── [drwx------] 1:1
> # +│ ├── [drwx------] 1:10
> # +│ ├── [drwx------] 1:11
> # +│ ├── [drwx------] 1:12
> # +│ ├── [drwx------] 1:13
> # +│ ├── [drwx------] 1:14
> # +│ ├── [drwx------] 1:15
> # +│ ├── [drwx------] 1:2
> # +│ ├── [drwx------] 1:3
> # +│ ├── [drwx------] 1:4
> # +│ ├── [drwx------] 1:5
> # +│ ├── [drwx------] 1:6
> # +│ ├── [drwx------] 1:7
> # +│ ├── [drwx------] 1:8
> # +│ ├── [drwx------] 1:9
> # +│ └── [drwx------] 94:0
> # +├── [drwx------] block
> # +├── [drwx------] dasd
> # +│ ├── [drwx------] 0.0.e18a
> # +│ ├── [drwx------] dasda
> # +│ └── [drwx------] global
> # +├── [drwx------] device_component
> # +├── [drwx------] extfrag
> # +├── [drwx------] hid
> # +├── [drwx------] kprobes
> # +├── [drwx------] kvm
> # +├── [drwx------] memblock
> # +├── [drwx------] pm_qos
> # +├── [drwx------] qdio
> # +│ └── [drwx------] 0.0.f5f2
> # +├── [drwx------] s390
> # +│ └── [drwx------] stsi
> # +├── [drwx------] s390dbf
> # +│ ├── [drwx------] 0.0.e18a
> # +│ ├── [drwx------] cio_crw
> # +│ ├── [drwx------] cio_msg
> # +│ ├── [drwx------] cio_trace
> # +│ ├── [drwx------] dasd
> # +│ ├── [drwx------] kvm-trace
> # +│ ├── [drwx------] lgr
> # +│ ├── [drwx------] qdio_0.0.f5f2
> # +│ ├── [drwx------] qdio_error
> # +│ ├── [drwx------] qdio_setup
> # +│ ├── [drwx------] qeth_card_0.0.f5f0
> # +│ ├── [drwx------] qeth_control
> # +│ ├── [drwx------] qeth_msg
> # +│ ├── [drwx------] qeth_setup
> # +│ ├── [drwx------] vmcp
> # +│ └── [drwx------] vmur
> # └── [drwx------] tracing
> # ├── [drwxr-xr-x] events
> # │ ├── [drwxr-xr-x] alarmtimer
>
> Fixes: edac65eaf8d5c ("debugfs: take mode-dependent parts of debugfs_get_inode() into callers")
> Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
> 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
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