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apparmor: fix aa_xattrs_match() may sleep while holding a RCU lock 

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: 8e51f9087f ("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>
This commit is contained in:
John Johansen 2020-01-02 05:31:22 -08:00
parent 20d4e80d25
commit 8c62ed27a1
3 changed files with 45 additions and 41 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
security/apparmor/apparmorfs.c
View File

@ -623,7 +623,7 @@ static __poll_t ns_revision_poll(struct file *file, poll_table *pt)
void __aa_bump_ns_revision(struct aa_ns *ns)
{
ns->revision++;
WRITE_ONCE(ns->revision, ns->revision + 1);
wake_up_interruptible(&ns->wait);
}

80
security/apparmor/domain.c
View File

@ -317,6 +317,7 @@ static int aa_xattrs_match(const struct linux_binprm *bprm,
if (!bprm || !profile->xattr_count)
return 0;
might_sleep();
/* transition from exec match to xattr set */
state = aa_dfa_null_transition(profile->xmatch, state);
@ -361,10 +362,11 @@ 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
@ -374,12 +376,11 @@ 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;
@ -388,6 +389,8 @@ static struct aa_profile *__attach_match(const struct linux_binprm *bprm,
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))
@ -413,16 +416,32 @@ static struct aa_profile *__attach_match(const struct linux_binprm *bprm,
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
*
@ -445,43 +464,28 @@ static struct aa_profile *__attach_match(const struct linux_binprm *bprm,
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)

4
security/apparmor/policy.c
View File

@ -1125,8 +1125,8 @@ ssize_t aa_remove_profiles(struct aa_ns *policy_ns, struct aa_label *subj,
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 */
@ -1138,9 +1138,9 @@ ssize_t aa_remove_profiles(struct aa_ns *policy_ns, struct aa_label *subj,
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);
}