Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965886AbeAOMlR (ORCPT + 1 other); Mon, 15 Jan 2018 07:41:17 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:46868 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965463AbeAOMlM (ORCPT ); Mon, 15 Jan 2018 07:41:12 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot+b0efb8e572d01bce1ae0@syzkaller.appspotmail.com, syzbot+6c15e9744f75f2364773@syzkaller.appspotmail.com, syzbot+d2f5524fb46fd3b312ee@syzkaller.appspotmail.com, syzbot+61d23c95395cc90dbc2b@syzkaller.appspotmail.com, syzbot+0d363c942452cca68c01@syzkaller.appspotmail.com, Daniel Borkmann , Alexei Starovoitov , Jiri Slaby Subject: [PATCH 4.4 69/87] bpf, array: fix overflow in max_entries and undefined behavior in index_mask Date: Mon, 15 Jan 2018 13:35:08 +0100 Message-Id: <20180115123356.998907077@linuxfoundation.org> X-Mailer: git-send-email 2.15.1 In-Reply-To: <20180115123349.252309699@linuxfoundation.org> References: <20180115123349.252309699@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Daniel Borkmann commit bbeb6e4323dad9b5e0ee9f60c223dd532e2403b1 upstream. syzkaller tried to alloc a map with 0xfffffffd entries out of a userns, and thus unprivileged. With the recently added logic in b2157399cc98 ("bpf: prevent out-of-bounds speculation") we round this up to the next power of two value for max_entries for unprivileged such that we can apply proper masking into potentially zeroed out map slots. However, this will generate an index_mask of 0xffffffff, and therefore a + 1 will let this overflow into new max_entries of 0. This will pass allocation, etc, and later on map access we still enforce on the original attr->max_entries value which was 0xfffffffd, therefore triggering GPF all over the place. Thus bail out on overflow in such case. Moreover, on 32 bit archs roundup_pow_of_two() can also not be used, since fls_long(max_entries - 1) can result in 32 and 1UL << 32 in 32 bit space is undefined. Therefore, do this by hand in a 64 bit variable. This fixes all the issues triggered by syzkaller's reproducers. Fixes: b2157399cc98 ("bpf: prevent out-of-bounds speculation") Reported-by: syzbot+b0efb8e572d01bce1ae0@syzkaller.appspotmail.com Reported-by: syzbot+6c15e9744f75f2364773@syzkaller.appspotmail.com Reported-by: syzbot+d2f5524fb46fd3b312ee@syzkaller.appspotmail.com Reported-by: syzbot+61d23c95395cc90dbc2b@syzkaller.appspotmail.com Reported-by: syzbot+0d363c942452cca68c01@syzkaller.appspotmail.com Signed-off-by: Daniel Borkmann Signed-off-by: Alexei Starovoitov Signed-off-by: Jiri Slaby Signed-off-by: Greg Kroah-Hartman --- kernel/bpf/arraymap.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) --- a/kernel/bpf/arraymap.c +++ b/kernel/bpf/arraymap.c @@ -23,6 +23,7 @@ static struct bpf_map *array_map_alloc(u u32 elem_size, array_size, index_mask, max_entries; bool unpriv = !capable(CAP_SYS_ADMIN); struct bpf_array *array; + u64 mask64; /* check sanity of attributes */ if (attr->max_entries == 0 || attr->key_size != 4 || @@ -38,13 +39,25 @@ static struct bpf_map *array_map_alloc(u elem_size = round_up(attr->value_size, 8); max_entries = attr->max_entries; - index_mask = roundup_pow_of_two(max_entries) - 1; - if (unpriv) + /* On 32 bit archs roundup_pow_of_two() with max_entries that has + * upper most bit set in u32 space is undefined behavior due to + * resulting 1U << 32, so do it manually here in u64 space. + */ + mask64 = fls_long(max_entries - 1); + mask64 = 1ULL << mask64; + mask64 -= 1; + + index_mask = mask64; + if (unpriv) { /* round up array size to nearest power of 2, * since cpu will speculate within index_mask limits */ max_entries = index_mask + 1; + /* Check for overflows. */ + if (max_entries < attr->max_entries) + return ERR_PTR(-E2BIG); + } /* check round_up into zero and u32 overflow */ if (elem_size == 0 ||