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authorNeilBrown <neilb@suse.de>2015-03-23 13:37:39 +1100
committerAl Viro <viro@zeniv.linux.org.uk>2015-05-11 08:13:11 -0400
commitbda0be7ad994812960e9f8f2d2757f72cb4a96cb (patch)
treef769e7c4511b64432438f82a8426248e75a8ad7b
parent7b20ea2579238f5e0da4bc93276c1b63c960c9ef (diff)
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: NeilBrown <neilb@suse.de> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--fs/namei.c5
-rw-r--r--include/linux/security.h12
-rw-r--r--security/capability.c3
-rw-r--r--security/security.c7
-rw-r--r--security/selinux/hooks.c16
5 files changed, 32 insertions, 11 deletions
diff --git a/fs/namei.c b/fs/namei.c
index 33b655de0ec0..0fa7af23cff6 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -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;
diff --git a/include/linux/security.h b/include/linux/security.h
index 62a66202ecf1..52febde52479 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -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;
}
diff --git a/security/capability.c b/security/capability.c
index fae99db180ca..7d3f38fe02ba 100644
--- a/security/capability.c
+++ b/security/capability.c
@@ -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;
}
diff --git a/security/security.c b/security/security.c
index d7c30b03e144..04c8feca081a 100644
--- a/security/security.c
+++ b/security/security.c
@@ -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)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index d56a82967d5e..ffa5a642629a 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -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,