Make sure that security_locked_down() is checked last so that a bogus
denial is not reported by SELinux when (ia->ia_valid & (ATTR_MODE |
ATTR_UID | ATTR_GID)) is zero.
Note: this was introduced by commit 5496197f9b08 ("debugfs: Restrict
debugfs when the kernel is locked down"), but it didn't matter at that
time, as the SELinux support came in later.
Fixes: 59438b46471a ("security,lockdown,selinux: implement SELinux lockdown")
Signed-off-by: Ondrej Mosnacek <[email protected]>
---
fs/debugfs/inode.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 22e86ae4dd5a..bbfc7898c1aa 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -45,10 +45,13 @@ static unsigned int debugfs_allow = DEFAULT_DEBUGFS_ALLOW_BITS;
static int debugfs_setattr(struct user_namespace *mnt_userns,
struct dentry *dentry, struct iattr *ia)
{
- int ret = security_locked_down(LOCKDOWN_DEBUGFS);
+ int ret;
- if (ret && (ia->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
- return ret;
+ if (ia->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)) {
+ ret = security_locked_down(LOCKDOWN_DEBUGFS);
+ if (ret)
+ return ret;
+ }
return simple_setattr(&init_user_ns, dentry, ia);
}
--
2.31.1
On Fri, May 07, 2021 at 01:41:50PM +0200, Ondrej Mosnacek wrote:
> Make sure that security_locked_down() is checked last so that a bogus
> denial is not reported by SELinux when (ia->ia_valid & (ATTR_MODE |
> ATTR_UID | ATTR_GID)) is zero.
Why would this be "bogus"?
> Note: this was introduced by commit 5496197f9b08 ("debugfs: Restrict
> debugfs when the kernel is locked down"), but it didn't matter at that
> time, as the SELinux support came in later.
>
> Fixes: 59438b46471a ("security,lockdown,selinux: implement SELinux lockdown")
What does this "fix"?
What is happening in selinux that it can not handle this sequence now?
That commit showed up a long time ago, this feels "odd"...
thanks,
greg k-h
On Fri, May 07, 2021 at 02:03:04PM +0200, Greg Kroah-Hartman wrote:
> On Fri, May 07, 2021 at 01:41:50PM +0200, Ondrej Mosnacek wrote:
> > Make sure that security_locked_down() is checked last so that a bogus
> > denial is not reported by SELinux when (ia->ia_valid & (ATTR_MODE |
> > ATTR_UID | ATTR_GID)) is zero.
>
> Why would this be "bogus"?
I presume selinux is logging a denial ... but we don't then actually
deny the operation.
> > Note: this was introduced by commit 5496197f9b08 ("debugfs: Restrict
> > debugfs when the kernel is locked down"), but it didn't matter at that
> > time, as the SELinux support came in later.
> >
> > Fixes: 59438b46471a ("security,lockdown,selinux: implement SELinux lockdown")
>
> What does this "fix"?
>
> What is happening in selinux that it can not handle this sequence now?
> That commit showed up a long time ago, this feels "odd"...
>
> thanks,
>
> greg k-h
On Fri, May 07, 2021 at 01:12:18PM +0100, Matthew Wilcox wrote:
> On Fri, May 07, 2021 at 02:03:04PM +0200, Greg Kroah-Hartman wrote:
> > On Fri, May 07, 2021 at 01:41:50PM +0200, Ondrej Mosnacek wrote:
> > > Make sure that security_locked_down() is checked last so that a bogus
> > > denial is not reported by SELinux when (ia->ia_valid & (ATTR_MODE |
> > > ATTR_UID | ATTR_GID)) is zero.
> >
> > Why would this be "bogus"?
>
> I presume selinux is logging a denial ... but we don't then actually
> deny the operation.
That would be nice to note here...
On Fri, May 7, 2021 at 2:16 PM Greg Kroah-Hartman
<[email protected]> wrote:
> On Fri, May 07, 2021 at 01:12:18PM +0100, Matthew Wilcox wrote:
> > On Fri, May 07, 2021 at 02:03:04PM +0200, Greg Kroah-Hartman wrote:
> > > On Fri, May 07, 2021 at 01:41:50PM +0200, Ondrej Mosnacek wrote:
> > > > Make sure that security_locked_down() is checked last so that a bogus
> > > > denial is not reported by SELinux when (ia->ia_valid & (ATTR_MODE |
> > > > ATTR_UID | ATTR_GID)) is zero.
> > >
> > > Why would this be "bogus"?
> >
> > I presume selinux is logging a denial ... but we don't then actually
> > deny the operation.
>
> That would be nice to note here...
Granted, I didn't do a good job of describing the issue in the patch
description... I'll send a v2 with hopefully a better description.
--
Ondrej Mosnacek
Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.