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device_cgroup: add proper checking when changing default behavior
Before changing a group's default behavior to ALLOW, we must check if its parent's behavior is also ALLOW. Signed-off-by: Aristeu Rozanski <aris@redhat.com> Cc: Tejun Heo <tj@kernel.org> Cc: Li Zefan <lizefan@huawei.com> Cc: James Morris <jmorris@namei.org> Cc: Pavel Emelyanov <xemul@openvz.org> Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Cc: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -344,6 +344,17 @@ static int parent_has_perm(struct dev_cgroup *childcg,
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return may_access(parent, ex);
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}
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/**
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* may_allow_all - checks if it's possible to change the behavior to
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* allow based on parent's rules.
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* @parent: device cgroup's parent
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* returns: != 0 in case it's allowed, 0 otherwise
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*/
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static inline int may_allow_all(struct dev_cgroup *parent)
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{
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return parent->behavior == DEVCG_DEFAULT_ALLOW;
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}
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/*
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* Modify the exception list using allow/deny rules.
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* CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD
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@ -364,6 +375,8 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
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char temp[12]; /* 11 + 1 characters needed for a u32 */
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int count, rc;
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struct dev_exception_item ex;
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struct cgroup *p = devcgroup->css.cgroup;
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struct dev_cgroup *parent = cgroup_to_devcgroup(p->parent);
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if (!capable(CAP_SYS_ADMIN))
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return -EPERM;
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@ -375,9 +388,13 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
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case 'a':
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switch (filetype) {
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case DEVCG_ALLOW:
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if (!parent_has_perm(devcgroup, &ex))
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if (!may_allow_all(parent))
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return -EPERM;
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dev_exception_clean(devcgroup);
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rc = dev_exceptions_copy(&devcgroup->exceptions,
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&parent->exceptions);
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if (rc)
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return rc;
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devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
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break;
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case DEVCG_DENY:
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