Commit bda0be7a authored by NeilBrown's avatar NeilBrown Committed by Al Viro
Browse files

security: make inode_follow_link RCU-walk aware 



inode_follow_link now takes an inode and rcu flag as well as the
dentry.

inode is used in preference to d_backing_inode(dentry), particularly
in RCU-walk mode.

selinux_inode_follow_link() gets dentry_has_perm() and
inode_has_perm() open-coded into it so that it can call
avc_has_perm_flags() in way that is safe if LOOKUP_RCU is set.

Calling avc_has_perm_flags() with rcu_read_lock() held means
that when avc_has_perm_noaudit calls avc_compute_av(), the attempt
to rcu_read_unlock() before calling security_compute_av() will not
actually drop the RCU read-lock.

However as security_compute_av() is completely in a read_lock()ed
region, it should be safe with the RCU read-lock held.

Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 7b20ea25

fs/namei.c

+3 −2
Original line number Diff line number Diff line
@@ -881,8 +881,9 @@ const char *get_link(struct nameidata *nd) 


	touch_atime(&last->link);



	error = security_inode_follow_link(dentry);

	if (error)

	error = security_inode_follow_link(dentry, inode,

					   nd->flags & LOOKUP_RCU);

	if (unlikely(error))

		return ERR_PTR(error);



	nd->last_type = LAST_BIND;

include/linux/security.h

+9 −3
Original line number Diff line number Diff line
@@ -476,6 +476,8 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts) 
 * @inode_follow_link:

 *	Check permission to follow a symbolic link when looking up a pathname.

 *	@dentry contains the dentry structure for the link.

 *	@inode contains the inode, which itself is not stable in RCU-walk

 *	@rcu indicates whether we are in RCU-walk mode.

 *	Return 0 if permission is granted.

 * @inode_permission:

 *	Check permission before accessing an inode.  This hook is called by the
@@ -1551,7 +1553,8 @@ struct security_operations { 
	int (*inode_rename) (struct inode *old_dir, struct dentry *old_dentry,

			     struct inode *new_dir, struct dentry *new_dentry);

	int (*inode_readlink) (struct dentry *dentry);

	int (*inode_follow_link) (struct dentry *dentry);

	int (*inode_follow_link) (struct dentry *dentry, struct inode *inode,

				  bool rcu);

	int (*inode_permission) (struct inode *inode, int mask);

	int (*inode_setattr)	(struct dentry *dentry, struct iattr *attr);

	int (*inode_getattr) (const struct path *path);
@@ -1837,7 +1840,8 @@ int security_inode_rename(struct inode *old_dir, struct dentry *old_dentry, 
			  struct inode *new_dir, struct dentry *new_dentry,

			  unsigned int flags);

int security_inode_readlink(struct dentry *dentry);

int security_inode_follow_link(struct dentry *dentry);

int security_inode_follow_link(struct dentry *dentry, struct inode *inode,

			       bool rcu);

int security_inode_permission(struct inode *inode, int mask);

int security_inode_setattr(struct dentry *dentry, struct iattr *attr);

int security_inode_getattr(const struct path *path);
@@ -2239,7 +2243,9 @@ static inline int security_inode_readlink(struct dentry *dentry) 
	return 0;

}



static inline int security_inode_follow_link(struct dentry *dentry)

static inline int security_inode_follow_link(struct dentry *dentry,

					     struct inode *inode,

					     bool rcu)

{

	return 0;

}

security/capability.c

+2 −1
Original line number Diff line number Diff line
@@ -209,7 +209,8 @@ static int cap_inode_readlink(struct dentry *dentry) 
	return 0;

}



static int cap_inode_follow_link(struct dentry *dentry)

static int cap_inode_follow_link(struct dentry *dentry, struct inode *inode,

				 bool rcu)

{

	return 0;

}

security/security.c

+4 −3
Original line number Diff line number Diff line
@@ -581,11 +581,12 @@ int security_inode_readlink(struct dentry *dentry) 
	return security_ops->inode_readlink(dentry);

}



int security_inode_follow_link(struct dentry *dentry)

int security_inode_follow_link(struct dentry *dentry, struct inode *inode,

			       bool rcu)

{

	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))

	if (unlikely(IS_PRIVATE(inode)))

		return 0;

	return security_ops->inode_follow_link(dentry);

	return security_ops->inode_follow_link(dentry, inode, rcu);

}



int security_inode_permission(struct inode *inode, int mask)

security/selinux/hooks.c

+14 −2
Original line number Diff line number Diff line
@@ -2861,11 +2861,23 @@ static int selinux_inode_readlink(struct dentry *dentry) 
	return dentry_has_perm(cred, dentry, FILE__READ);

}



static int selinux_inode_follow_link(struct dentry *dentry)

static int selinux_inode_follow_link(struct dentry *dentry, struct inode *inode,

				     bool rcu)

{

	const struct cred *cred = current_cred();

	struct common_audit_data ad;

	struct inode_security_struct *isec;

	u32 sid;



	return dentry_has_perm(cred, dentry, FILE__READ);

	validate_creds(cred);



	ad.type = LSM_AUDIT_DATA_DENTRY;

	ad.u.dentry = dentry;

	sid = cred_sid(cred);

	isec = inode->i_security;



	return avc_has_perm_flags(sid, isec->sid, isec->sclass, FILE__READ, &ad,

				  rcu ? MAY_NOT_BLOCK : 0);

}



static noinline int audit_inode_permission(struct inode *inode,

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