From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B9EDC134A4 for ; Mon, 12 Jun 2023 10:41:25 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1B76BC433EF; Mon, 12 Jun 2023 10:41:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1686566485; bh=zuteXLUzs2XJRYve8URZRigyEklO1ZTKtkGGHiDZdA8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TlcIHmKJmHHYKct8nOPElOU1V7Is4/WV64Ygq5rCiBbXQTgThTfsa2Mc9rXsw27jl g1dZKoefle9sZs3sQ9bTNBubIZvNH/e0M5N7FpAk3vX5QnuieFDhZYkglJ0Cq1h1xo 8I/bKr6tGsx/pdbZN07IrFhwH32/4oiyIDygyQ0c= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Anastasios Papagiannis , Alexei Starovoitov , Jiri Olsa , Daniel Borkmann , Stanislav Fomichev , Yonghong Song , Sasha Levin Subject: [PATCH 6.1 049/132] bpf: Add extra path pointer check to d_path helper Date: Mon, 12 Jun 2023 12:26:23 +0200 Message-ID: <20230612101712.490564448@linuxfoundation.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230612101710.279705932@linuxfoundation.org> References: <20230612101710.279705932@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Jiri Olsa [ Upstream commit f46fab0e36e611a2389d3843f34658c849b6bd60 ] Anastasios reported crash on stable 5.15 kernel with following BPF attached to lsm hook: SEC("lsm.s/bprm_creds_for_exec") int BPF_PROG(bprm_creds_for_exec, struct linux_binprm *bprm) { struct path *path = &bprm->executable->f_path; char p[128] = { 0 }; bpf_d_path(path, p, 128); return 0; } But bprm->executable can be NULL, so bpf_d_path call will crash: BUG: kernel NULL pointer dereference, address: 0000000000000018 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC NOPTI ... RIP: 0010:d_path+0x22/0x280 ... Call Trace: bpf_d_path+0x21/0x60 bpf_prog_db9cf176e84498d9_bprm_creds_for_exec+0x94/0x99 bpf_trampoline_6442506293_0+0x55/0x1000 bpf_lsm_bprm_creds_for_exec+0x5/0x10 security_bprm_creds_for_exec+0x29/0x40 bprm_execve+0x1c1/0x900 do_execveat_common.isra.0+0x1af/0x260 __x64_sys_execve+0x32/0x40 It's problem for all stable trees with bpf_d_path helper, which was added in 5.9. This issue is fixed in current bpf code, where we identify and mark trusted pointers, so the above code would fail even to load. For the sake of the stable trees and to workaround potentially broken verifier in the future, adding the code that reads the path object from the passed pointer and verifies it's valid in kernel space. Fixes: 6e22ab9da793 ("bpf: Add d_path helper") Reported-by: Anastasios Papagiannis Suggested-by: Alexei Starovoitov Signed-off-by: Jiri Olsa Signed-off-by: Daniel Borkmann Acked-by: Stanislav Fomichev Acked-by: Yonghong Song Link: https://lore.kernel.org/bpf/20230606181714.532998-1-jolsa@kernel.org Signed-off-by: Sasha Levin --- kernel/trace/bpf_trace.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 9d4163abadf4e..1642548892a8e 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -903,13 +903,23 @@ static const struct bpf_func_proto bpf_send_signal_thread_proto = { BPF_CALL_3(bpf_d_path, struct path *, path, char *, buf, u32, sz) { + struct path copy; long len; char *p; if (!sz) return 0; - p = d_path(path, buf, sz); + /* + * The path pointer is verified as trusted and safe to use, + * but let's double check it's valid anyway to workaround + * potentially broken verifier. + */ + len = copy_from_kernel_nofault(©, path, sizeof(*path)); + if (len < 0) + return len; + + p = d_path(©, buf, sz); if (IS_ERR(p)) { len = PTR_ERR(p); } else { -- 2.39.2