fs: Avoid premature clearing of capabilities (030b533c) · Commits · 戴 / test

Currently, notify_change() clears capabilities or IMA attributes by calling security_inode_killpriv() before calling into ->setattr. Thus it happens before any other permission checks in inode_change_ok() and user is thus allowed to trigger clearing of capabilities or IMA attributes for any file he can look up e.g. by calling chown for that file. This is unexpected and can lead to user DoSing a system. Fix the problem by calling security_inode_killpriv() at the end of inode_change_ok() instead of from notify_change(). At that moment we are sure user has permissions to do the requested change. References: CVE-2015-1350 Reviewed-by:

Christoph Hellwig <hch@lst.de> Signed-off-by:

Jan Kara <jack@suse.cz>

fs/attr.c

+14 −6

Original line number	Diff line number	Diff line
		@@ -47,7 +47,7 @@ int setattr_prepare(struct dentry dentry, struct iattr attr)

		/* If force is set do it anyway. */
		if (ia_valid & ATTR_FORCE)
		return 0;
		goto kill_priv;

		/* Make sure a caller can chown. */
		if ((ia_valid & ATTR_UID) &&
		@@ -80,6 +80,16 @@ int setattr_prepare(struct dentry dentry, struct iattr attr)
		return -EPERM;
		}

		kill_priv:
		/* User has permission for the change */
		if (ia_valid & ATTR_KILL_PRIV) {
		int error;

		error = security_inode_killpriv(dentry);
		if (error)
		return error;
		}

		return 0;
		}
		EXPORT_SYMBOL(setattr_prepare);
		@@ -220,13 +230,11 @@ int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **de
		if (!(ia_valid & ATTR_MTIME_SET))
		attr->ia_mtime = now;
		if (ia_valid & ATTR_KILL_PRIV) {
		attr->ia_valid &= ~ATTR_KILL_PRIV;
		ia_valid &= ~ATTR_KILL_PRIV;
		error = security_inode_need_killpriv(dentry);
		if (error > 0)
		error = security_inode_killpriv(dentry);
		if (error)
		if (error < 0)
		return error;
		if (error == 0)
		ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
		}

		/*

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