From: Maciej Żenczykowski <[email protected]>
Currently a non-root process can create directories, but cannot
create stuff in the directories it creates.
Example (before this patch):
phone:/ $ id
uid=1000(system) gid=1000(system) groups=1000(system),... context=u:r:su:s0
phone:/ $ cd /config/usb_gadget/g1/configs/
phone:/config/usb_gadget/g1/configs $ ls -lZ
drwxr-xr-x 3 system system u:object_r:configfs:s0 0 2020-12-28 06:03 b.1
phone:/config/usb_gadget/g1/configs $ mkdir b.2
phone:/config/usb_gadget/g1/configs $ ls -lZ
drwxr-xr-x 3 system system u:object_r:configfs:s0 0 2020-12-28 06:03 b.1
drwxr-xr-x 3 root root u:object_r:configfs:s0 0 2020-12-28 06:51 b.2
phone:/config/usb_gadget/g1/configs $ chown system:system b.2
chown: 'b.2' to 'system:system': Operation not permitted
phone:/config/usb_gadget/g1/configs $ ls -lZ b.1
-rw-r--r-- 1 system system u:object_r:configfs:s0 4096 2020-12-28 05:23 MaxPower
-rw-r--r-- 1 system system u:object_r:configfs:s0 4096 2020-12-28 05:23 bmAttributes
lrwxrwxrwx 1 root root u:object_r:configfs:s0 0 2020-12-28 05:23 function0 -> ../../../../usb_gadget/g1/functions/ffs.adb
drwxr-xr-x 2 system system u:object_r:configfs:s0 0 2020-12-28 05:23 strings
phone:/config/usb_gadget/g1/configs $ ln -s ../../../../usb_gadget/g1/functions/ffs.adb b.2/function0
ln: cannot create symbolic link from '../../../../usb_gadget/g1/functions/ffs.adb' to 'b.2/function0': Permission denied
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Joel Becker <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Signed-off-by: Maciej Żenczykowski <[email protected]>
Change-Id: Ia907b2def940197b44aa87b337d37c5dde9c5b91
---
fs/configfs/dir.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index b839dd1b459f..04f18402ef7c 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -1410,6 +1410,21 @@ static int configfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode
else
ret = configfs_attach_item(parent_item, item, dentry, frag);
+ /* inherit uid/gid from process creating the directory */
+ if (!uid_eq(current_fsuid(), GLOBAL_ROOT_UID) ||
+ !gid_eq(current_fsgid(), GLOBAL_ROOT_GID)) {
+ struct inode * inode = d_inode(dentry);
+ struct iattr ia = {
+ .ia_uid = current_fsuid(),
+ .ia_gid = current_fsgid(),
+ .ia_valid = ATTR_UID | ATTR_GID,
+ };
+ inode->i_uid = ia.ia_uid;
+ inode->i_gid = ia.ia_gid;
+ /* (note: the above manual assignments skip the permission checks) */
+ (void)configfs_setattr(dentry, &ia);
+ }
+
spin_lock(&configfs_dirent_lock);
sd->s_type &= ~CONFIGFS_USET_IN_MKDIR;
if (!ret)
--
2.30.0.280.ga3ce27912f-goog
On Sat, Jan 23, 2021 at 12:55:16PM -0800, Maciej Żenczykowski wrote:
> From: Maciej Żenczykowski <[email protected]>
>
> Currently a non-root process can create directories, but cannot
> create stuff in the directories it creates.
Isn't that on purpose?
>
> Example (before this patch):
> phone:/ $ id
> uid=1000(system) gid=1000(system) groups=1000(system),... context=u:r:su:s0
>
> phone:/ $ cd /config/usb_gadget/g1/configs/
>
> phone:/config/usb_gadget/g1/configs $ ls -lZ
> drwxr-xr-x 3 system system u:object_r:configfs:s0 0 2020-12-28 06:03 b.1
>
> phone:/config/usb_gadget/g1/configs $ mkdir b.2
>
> phone:/config/usb_gadget/g1/configs $ ls -lZ
> drwxr-xr-x 3 system system u:object_r:configfs:s0 0 2020-12-28 06:03 b.1
> drwxr-xr-x 3 root root u:object_r:configfs:s0 0 2020-12-28 06:51 b.2
>
> phone:/config/usb_gadget/g1/configs $ chown system:system b.2
> chown: 'b.2' to 'system:system': Operation not permitted
>
> phone:/config/usb_gadget/g1/configs $ ls -lZ b.1
> -rw-r--r-- 1 system system u:object_r:configfs:s0 4096 2020-12-28 05:23 MaxPower
> -rw-r--r-- 1 system system u:object_r:configfs:s0 4096 2020-12-28 05:23 bmAttributes
> lrwxrwxrwx 1 root root u:object_r:configfs:s0 0 2020-12-28 05:23 function0 -> ../../../../usb_gadget/g1/functions/ffs.adb
> drwxr-xr-x 2 system system u:object_r:configfs:s0 0 2020-12-28 05:23 strings
>
> phone:/config/usb_gadget/g1/configs $ ln -s ../../../../usb_gadget/g1/functions/ffs.adb b.2/function0
> ln: cannot create symbolic link from '../../../../usb_gadget/g1/functions/ffs.adb' to 'b.2/function0': Permission denied
>
> Cc: Greg Kroah-Hartman <[email protected]>
> Cc: Joel Becker <[email protected]>
> Cc: Christoph Hellwig <[email protected]>
> Signed-off-by: Maciej Żenczykowski <[email protected]>
> Change-Id: Ia907b2def940197b44aa87b337d37c5dde9c5b91
No need for "Change-Id:" :)
> ---
> fs/configfs/dir.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
> index b839dd1b459f..04f18402ef7c 100644
> --- a/fs/configfs/dir.c
> +++ b/fs/configfs/dir.c
> @@ -1410,6 +1410,21 @@ static int configfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode
> else
> ret = configfs_attach_item(parent_item, item, dentry, frag);
>
> + /* inherit uid/gid from process creating the directory */
> + if (!uid_eq(current_fsuid(), GLOBAL_ROOT_UID) ||
> + !gid_eq(current_fsgid(), GLOBAL_ROOT_GID)) {
> + struct inode * inode = d_inode(dentry);
> + struct iattr ia = {
> + .ia_uid = current_fsuid(),
> + .ia_gid = current_fsgid(),
> + .ia_valid = ATTR_UID | ATTR_GID,
> + };
> + inode->i_uid = ia.ia_uid;
> + inode->i_gid = ia.ia_gid;
> + /* (note: the above manual assignments skip the permission checks) */
> + (void)configfs_setattr(dentry, &ia);
No need for (void), here, right?
And this feels like a big user-visible change, what is going to break
with this?
thanks,
greg k-h
> > Currently a non-root process can create directories, but cannot
> > create stuff in the directories it creates.
>
> Isn't that on purpose?
Is it? What's the use case of being able to create empty directories
you can't use?
Why allow their creation in the first place then?
> > + (void)configfs_setattr(dentry, &ia);
>
> No need for (void), here, right?
Just being clear we're ignoring any potential error return.
> And this feels like a big user-visible change, what is going to break
> with this?
That I don't know, but it's unlikely to break anything, since it's virtually
impossible to use as it is now. If non-root creates the directory, it's
currently root-owned, so can only be used by root (or something with
appropriate caps).
Something with capabilities will be able to use it even if it is no
longer owned by root.