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>
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@@ -581,11 +581,12 @@ int security_inode_readlink(struct dentry *dentry)
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return security_ops->inode_readlink(dentry);
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}
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int security_inode_follow_link(struct dentry *dentry)
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int security_inode_follow_link(struct dentry *dentry, struct inode *inode,
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bool rcu)
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{
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if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
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if (unlikely(IS_PRIVATE(inode)))
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return 0;
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return security_ops->inode_follow_link(dentry);
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return security_ops->inode_follow_link(dentry, inode, rcu);
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}
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int security_inode_permission(struct inode *inode, int mask)
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