From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jann Horn Subject: [PATCH] bpf: fix double-fdput in replace_map_fd_with_map_ptr() Date: Tue, 26 Apr 2016 22:26:26 +0200 Message-ID: <1461702386-17490-1-git-send-email-jannh@google.com> Cc: netdev@vger.kernel.org, Jann Horn To: David Miller Return-path: Received: from mail-wm0-f53.google.com ([74.125.82.53]:37758 "EHLO mail-wm0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753829AbcDZU0c (ORCPT ); Tue, 26 Apr 2016 16:26:32 -0400 Received: by mail-wm0-f53.google.com with SMTP id n3so21736116wmn.0 for ; Tue, 26 Apr 2016 13:26:31 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: When bpf(BPF_PROG_LOAD, ...) was invoked with a BPF program whose bytecode references a non-map file descriptor as a map file descriptor, the error handling code called fdput() twice instead of once (in __bpf_map_get() and in replace_map_fd_with_map_ptr()). If the file descriptor table of the current task is shared, this causes f_count to be decremented too much, allowing the struct file to be freed while it is still in use (use-after-free). This can be exploited to gain root privileges by an unprivileged user. This bug was introduced in commit 0246e64d9a5f ("bpf: handle pseudo BPF_LD_IMM64 insn"), but is only exploitable since commit 1be7f75d1668 ("bpf: enable non-root eBPF programs") because previously, CAP_SYS_ADMIN was required to reach the vulnerable code. (posted publicly according to request by maintainer) Signed-off-by: Jann Horn Signed-off-by: Linus Torvalds --- kernel/bpf/verifier.c | 1 - 1 file changed, 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 2e08f8e..8291251 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2029,7 +2029,6 @@ static int replace_map_fd_with_map_ptr(struct verifier_env *env) if (IS_ERR(map)) { verbose("fd %d is not pointing to valid bpf_map\n", insn->imm); - fdput(f); return PTR_ERR(map); } -- 2.8.0.rc3.226.g39d4020