[PATCH 4.19 073/115] apparmor: fix aa_xattrs_match() may sleep while holding a RCU lock

Greg Kroah-Hartman
2020-01-07T21:16:51Z

From: John Johansen <john.johansen@canonical.com>

commit 8c62ed27a12c00e3db1c9f04bc0f272bdbb06734 upstream.

aa_xattrs_match() is unfortunately calling vfs_getxattr_alloc() from a
context protected by an rcu_read_lock. This can not be done as
vfs_getxattr_alloc() may sleep regardles of the gfp_t value being
passed to it.

Fix this by breaking the rcu_read_lock on the policy search when the
xattr match feature is requested and restarting the search if a policy
changes occur.

Fixes: 8e51f9087f40 ("apparmor: Add support for attaching profiles via xattr, presence and value")
Reported-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
security/apparmor/apparmorfs.c | 2 -
security/apparmor/domain.c | 80 +++++++++++++++++++++--------------------
security/apparmor/policy.c | 4 +-
3 files changed, 45 insertions(+), 41 deletions(-)

--- a/security/apparmor/apparmorfs.c
+++ b/security/apparmor/apparmorfs.c
@@ -593,7 +593,7 @@ static __poll_t ns_revision_poll(struct

void __aa_bump_ns_revision(struct aa_ns *ns)
{
- ns->revision++;
+ WRITE_ONCE(ns->revision, ns->revision + 1);
wake_up_interruptible(&ns->wait);
}

--- a/security/apparmor/domain.c
+++ b/security/apparmor/domain.c
@@ -321,6 +321,7 @@ static int aa_xattrs_match(const struct

if (!bprm || !profile->xattr_count)
return 0;
+ might_sleep();

/* transition from exec match to xattr set */
state = aa_dfa_null_transition(profile->xmatch, state);
@@ -365,10 +366,11 @@ out:
}

/**
- * __attach_match_ - find an attachment match
+ * find_attach - do attachment search for unconfined processes
* @bprm - binprm structure of transitioning task
- * @name - to match against (NOT NULL)
+ * @ns: the current namespace (NOT NULL)
* @head - profile list to walk (NOT NULL)
+ * @name - to match against (NOT NULL)
* @info - info message if there was an error (NOT NULL)
*
* Do a linear search on the profiles in the list. There is a matching
@@ -378,12 +380,11 @@ out:
*
* Requires: @head not be shared or have appropriate locks held
*
- * Returns: profile or NULL if no match found
+ * Returns: label or NULL if no match found
*/
-static struct aa_profile *__attach_match(const struct linux_binprm *bprm,
- const char *name,
- struct list_head *head,
- const char **info)
+static struct aa_label *find_attach(const struct linux_binprm *bprm,
+ struct aa_ns *ns, struct list_head *head,
+ const char *name, const char **info)
{
int candidate_len = 0, candidate_xattrs = 0;
bool conflict = false;
@@ -392,6 +393,8 @@ static struct aa_profile *__attach_match
AA_BUG(!name);
AA_BUG(!head);

+ rcu_read_lock();
+restart:
list_for_each_entry_rcu(profile, head, base.list) {
if (profile->label.flags & FLAG_NULL &&
&profile->label == ns_unconfined(profile->ns))
@@ -417,16 +420,32 @@ static struct aa_profile *__attach_match
perm = dfa_user_allow(profile->xmatch, state);
/* any accepting state means a valid match. */
if (perm & MAY_EXEC) {
- int ret;
+ int ret = 0;

if (count < candidate_len)
continue;

- ret = aa_xattrs_match(bprm, profile, state);
- /* Fail matching if the xattrs don't match */
- if (ret < 0)
- continue;
+ if (bprm && profile->xattr_count) {
+ long rev = READ_ONCE(ns->revision);

+ if (!aa_get_profile_not0(profile))
+ goto restart;
+ rcu_read_unlock();
+ ret = aa_xattrs_match(bprm, profile,
+ state);
+ rcu_read_lock();
+ aa_put_profile(profile);
+ if (rev !=
+ READ_ONCE(ns->revision))
+ /* policy changed */
+ goto restart;
+ /*
+ * Fail matching if the xattrs don't
+ * match
+ */
+ if (ret < 0)
+ continue;
+ }
/*
* TODO: allow for more flexible best match
*
@@ -449,43 +468,28 @@ static struct aa_profile *__attach_match
candidate_xattrs = ret;
conflict = false;
}
- } else if (!strcmp(profile->base.name, name))
+ } else if (!strcmp(profile->base.name, name)) {
/*
* old exact non-re match, without conditionals such
* as xattrs. no more searching required
*/
- return profile;
+ candidate = profile;
+ goto out;
+ }
}

- if (conflict) {
- *info = "conflicting profile attachments";
+ if (!candidate || conflict) {
+ if (conflict)
+ *info = "conflicting profile attachments";
+ rcu_read_unlock();
return NULL;
}

- return candidate;
-}
-
-/**
- * find_attach - do attachment search for unconfined processes
- * @bprm - binprm structure of transitioning task
- * @ns: the current namespace (NOT NULL)
- * @list: list to search (NOT NULL)
- * @name: the executable name to match against (NOT NULL)
- * @info: info message if there was an error
- *
- * Returns: label or NULL if no match found
- */
-static struct aa_label *find_attach(const struct linux_binprm *bprm,
- struct aa_ns *ns, struct list_head *list,
- const char *name, const char **info)
-{
- struct aa_profile *profile;
-
- rcu_read_lock();
- profile = aa_get_profile(__attach_match(bprm, name, list, info));
+out:
+ candidate = aa_get_newest_profile(candidate);
rcu_read_unlock();

- return profile ? &profile->label : NULL;
+ return &candidate->label;
}

static const char *next_name(int xtype, const char *name)
--- a/security/apparmor/policy.c
+++ b/security/apparmor/policy.c
@@ -1126,8 +1126,8 @@ ssize_t aa_remove_profiles(struct aa_ns
if (!name) {
/* remove namespace - can only happen if fqname[0] == ':' */
mutex_lock_nested(&ns->parent->lock, ns->level);
- __aa_remove_ns(ns);
__aa_bump_ns_revision(ns);
+ __aa_remove_ns(ns);
mutex_unlock(&ns->parent->lock);
} else {
/* remove profile */
@@ -1139,9 +1139,9 @@ ssize_t aa_remove_profiles(struct aa_ns
goto fail_ns_lock;
}
name = profile->base.hname;
+ __aa_bump_ns_revision(ns);
__remove_profile(profile);
__aa_labelset_update_subtree(ns);
- __aa_bump_ns_revision(ns);
mutex_unlock(&ns->lock);
}