vfs: coredumping fix

fix: http://bugzilla.kernel.org/show_bug.cgi?id=3043

only allow coredumping to the same uid that the coredumping
task runs under.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Acked-by: NAlan Cox <alan@redhat.com>
Acked-by: NChristoph Hellwig <hch@lst.de>
Acked-by: NAl Viro <viro@ftp.linux.org.uk>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/exec.c

@@ -1780,6 +1780,12 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs)
 	   but keep the previous behaviour for now. */
 	if (!ispipe && !S_ISREG(inode->i_mode))
 		goto close_fail;
+	/*
+	 * Dont allow local users get cute and trick others to coredump
+	 * into their pre-created files:
+	 */
+	if (inode->i_uid != current->fsuid)
+		goto close_fail;
 	if (!file->f_op)
 		goto close_fail;
 	if (!file->f_op->write)