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debugfs: fix security_locked_down() call for SELinux

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When (ia->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)) is zero, then
the SELinux implementation of the locked_down hook might report a denial
even though the operation would actually be allowed.

To fix this, make sure that security_locked_down() is called only when
the return value will be taken into account (i.e. when changing one of
the problematic attributes).

Note: this was introduced by commit 5496197f9b ("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: 59438b4647 ("security,lockdown,selinux: implement SELinux lockdown")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Link: https://lore.kernel.org/r/20210507125304.144394-1-omosnace@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ondrej Mosnacek 2021-05-07 14:53:04 +02:00 committed by Greg Kroah-Hartman
parent d07f6ca923
commit 5881fa8dc2
1 changed files with 6 additions and 3 deletions
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9
fs/debugfs/inode.c
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@ -45,10 +45,13 @@ static unsigned int debugfs_allow __ro_after_init = 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);
}