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userns: limit the maximum depth of user_namespace->parent chain
commit 8742f229b635bf1c1c84a3dfe5e47c814c20b5c8 upstream. Ensure that user_namespace->parent chain can't grow too much. Currently we use the hardroded 32 as limit. Reported-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -23,6 +23,7 @@ struct user_namespace {
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struct uid_gid_map projid_map;
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struct uid_gid_map projid_map;
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atomic_t count;
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atomic_t count;
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struct user_namespace *parent;
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struct user_namespace *parent;
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int level;
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kuid_t owner;
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kuid_t owner;
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kgid_t group;
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kgid_t group;
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unsigned int proc_inum;
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unsigned int proc_inum;
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@ -62,6 +62,9 @@ int create_user_ns(struct cred *new)
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kgid_t group = new->egid;
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kgid_t group = new->egid;
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int ret;
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int ret;
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if (parent_ns->level > 32)
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return -EUSERS;
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/*
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/*
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* Verify that we can not violate the policy of which files
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* Verify that we can not violate the policy of which files
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* may be accessed that is specified by the root directory,
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* may be accessed that is specified by the root directory,
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@ -92,6 +95,7 @@ int create_user_ns(struct cred *new)
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atomic_set(&ns->count, 1);
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atomic_set(&ns->count, 1);
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/* Leave the new->user_ns reference with the new user namespace. */
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/* Leave the new->user_ns reference with the new user namespace. */
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ns->parent = parent_ns;
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ns->parent = parent_ns;
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ns->level = parent_ns->level + 1;
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ns->owner = owner;
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ns->owner = owner;
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ns->group = group;
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ns->group = group;
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