From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Turner Subject: [PATCH v6 04/19] index-helper: add --strict Date: Wed, 27 Apr 2016 16:04:26 -0400 Message-ID: <1461787481-877-5-git-send-email-dturner@twopensource.com> References: <1461787481-877-1-git-send-email-dturner@twopensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: David Turner To: git@vger.kernel.org, pclouds@gmail.com X-From: git-owner@vger.kernel.org Wed Apr 27 22:06:57 2016 Return-path: Envelope-to: gcvg-git-2@plane.gmane.org Received: from vger.kernel.org ([209.132.180.67]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1avVjb-0003mY-8m for gcvg-git-2@plane.gmane.org; Wed, 27 Apr 2016 22:06:55 +0200 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753718AbcD0UGj convert rfc822-to-quoted-printable (ORCPT ); Wed, 27 Apr 2016 16:06:39 -0400 Received: from mail-qg0-f47.google.com ([209.85.192.47]:32931 "EHLO mail-qg0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753289AbcD0UFP (ORCPT ); Wed, 27 Apr 2016 16:05:15 -0400 Received: by mail-qg0-f47.google.com with SMTP id f92so21851399qgf.0 for ; Wed, 27 Apr 2016 13:05:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=twopensource-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=u1ayJN0OnKkGPQLe/5cPzcSb0lKMpcGYve1swLPH/uw=; b=CYMEaqr9H8rJLG8nUcprrWrGadxzVYu4l99PhG0FYW4cYyVKlMqGZc1K5hBVkadd5c u7WAwRtjbxaG4QeHdQpkxB888gCWqKw3LhR5LGloQAg+CENAoZG88dGdWYWZz4jYPKlc 4fDXHe0AtXUdzN7TKJJKxVgMNNE3007yOMUe59zJxYREqczSq5A725nDahil2mSx595I Bi1JFocwENgidVbBeZkXKnBWKmYbNv+HUbSpZz4gZfKiToUdlvQk5Jl7ihKqThsp5quP 91ntlh3yRPJTWd/4rve3nQPRGtbuVDTKkbRCVd7jElJIKz+TF1Ryv43ABy3P0+tOYi1p QGxQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=u1ayJN0OnKkGPQLe/5cPzcSb0lKMpcGYve1swLPH/uw=; b=Rr0UM/uxPp3l65fctloV6MkOjSmXeEcSHaR4ofUt//PIeDXN095nXNN5wfS//6GSxF 0YNakja7NE6+Lp64701/urs0t5JISw62hu3dsOrvhpUTKmebISF5xW4RQjeBgOjMimPD Tzx3pdYd+WNez9xYa1auw7H1f7VVCb3V8zOBioTJSPZ7iAt5yh6oUiB/XqRDTMwwh/hn oXm8/4UNejYz5SQ25jNLS0npRjP38exy1srrBvXTz8W8wglj/aiZMVh3MXNKrBR1D3Mk 9vF6yqsZxz5G+lxOWY4HKkYiZVbfYn0vCRxh2zPOi3tirWuCbblTRCP1rLkicdM6daNG LGGQ== X-Gm-Message-State: AOPr4FUDGI+yHFprt+k6oaf99Ornzkra5QL2lpOXmok3afg4rddRrqog/yjNxKKPvwiF8w== X-Received: by 10.140.238.76 with SMTP id j73mr11022276qhc.24.1461787513848; Wed, 27 Apr 2016 13:05:13 -0700 (PDT) Received: from ubuntu.twitter.biz ([192.133.79.145]) by smtp.gmail.com with ESMTPSA id r124sm1700085qhr.48.2016.04.27.13.05.12 (version=TLSv1/SSLv3 cipher=OTHER); Wed, 27 Apr 2016 13:05:13 -0700 (PDT) X-Mailer: git-send-email 2.4.2.767.g62658d5-twtrsrc In-Reply-To: <1461787481-877-1-git-send-email-dturner@twopensource.com> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Archived-At: =46rom: Nguy=E1=BB=85n Th=C3=A1i Ng=E1=BB=8Dc Duy There are "holes" in the index-helper approach because the shared memory is not verified again by git. If $USER is compromised, shared memory could be modified. But anyone who could do this could already modify $GIT_DIR/index. A more realistic risk is some bugs in index-helper that produce corrupt shared memory. --strict is added to avoid that. Strictly speaking there's still a very small gap where corrupt shared memory could still be read by git: after we write the trailing SHA-1 in the shared memory (thus signaling "this shm is ready") and before verify_shm() detects an error. Signed-off-by: Nguy=E1=BB=85n Th=C3=A1i Ng=E1=BB=8Dc Duy Signed-off-by: David Turner --- Documentation/git-index-helper.txt | 9 +++++++ cache.h | 1 + index-helper.c | 48 ++++++++++++++++++++++++++++++= ++++++++ read-cache.c | 9 ++++--- 4 files changed, 64 insertions(+), 3 deletions(-) diff --git a/Documentation/git-index-helper.txt b/Documentation/git-ind= ex-helper.txt index 77687c0..a5c058f 100644 --- a/Documentation/git-index-helper.txt +++ b/Documentation/git-index-helper.txt @@ -22,6 +22,15 @@ OPTIONS Exit if the cached index is not accessed for `` seconds. Specify 0 to wait forever. Default is 600. =20 +--strict:: +--no-strict:: + Strict mode makes index-helper verify the shared memory after + it's created. If the result does not match what's read from + $GIT_DIR/index, the shared memory is destroyed. This makes + index-helper take more than double the amount of time required + for reading an index, but because it will happen in the + background, it's not noticable. `--strict` is enabled by default. + NOTES ----- =20 diff --git a/cache.h b/cache.h index 43fb314..4b678e9 100644 --- a/cache.h +++ b/cache.h @@ -336,6 +336,7 @@ struct index_state { keep_mmap : 1, from_shm : 1, to_shm : 1, + always_verify_trailing_sha1 : 1, initialized : 1; struct hashmap name_hash; struct hashmap dir_hash; diff --git a/index-helper.c b/index-helper.c index 976e913..5cadd0d 100644 --- a/index-helper.c +++ b/index-helper.c @@ -17,6 +17,7 @@ struct shm { =20 static struct shm shm_index; static struct shm shm_base_index; +static int to_verify =3D 1; =20 static void release_index_shm(struct shm *is) { @@ -111,11 +112,56 @@ static void share_index(struct index_state *istat= e, struct shm *is) hashcpy((unsigned char *)new_mmap + istate->mmap_size - 20, is->sha1)= ; } =20 +static int verify_shm(void) +{ + int i; + struct index_state istate; + memset(&istate, 0, sizeof(istate)); + istate.always_verify_trailing_sha1 =3D 1; + istate.to_shm =3D 1; + i =3D read_index(&istate); + if (i !=3D the_index.cache_nr) + goto done; + for (; i < the_index.cache_nr; i++) { + struct cache_entry *base, *ce; + /* namelen is checked separately */ + const unsigned int ondisk_flags =3D + CE_STAGEMASK | CE_VALID | CE_EXTENDED_FLAGS; + unsigned int ce_flags, base_flags, ret; + base =3D the_index.cache[i]; + ce =3D istate.cache[i]; + if (ce->ce_namelen !=3D base->ce_namelen || + strcmp(ce->name, base->name)) { + warning("mismatch at entry %d", i); + break; + } + ce_flags =3D ce->ce_flags; + base_flags =3D base->ce_flags; + /* only on-disk flags matter */ + ce->ce_flags &=3D ondisk_flags; + base->ce_flags &=3D ondisk_flags; + ret =3D memcmp(&ce->ce_stat_data, &base->ce_stat_data, + offsetof(struct cache_entry, name) - + offsetof(struct cache_entry, ce_stat_data)); + ce->ce_flags =3D ce_flags; + base->ce_flags =3D base_flags; + if (ret) { + warning("mismatch at entry %d", i); + break; + } + } +done: + discard_index(&istate); + return i =3D=3D the_index.cache_nr; +} + static void share_the_index(void) { if (the_index.split_index && the_index.split_index->base) share_index(the_index.split_index->base, &shm_base_index); share_index(&the_index, &shm_index); + if (to_verify && !verify_shm()) + cleanup_shm(); discard_index(&the_index); } =20 @@ -255,6 +301,8 @@ int main(int argc, char **argv) struct option options[] =3D { OPT_INTEGER(0, "exit-after", &idle_in_seconds, N_("exit if not used after some seconds")), + OPT_BOOL(0, "strict", &to_verify, + "verify shared memory after creating"), OPT_END() }; =20 diff --git a/read-cache.c b/read-cache.c index 81dfb4e..9eedf03 100644 --- a/read-cache.c +++ b/read-cache.c @@ -1671,9 +1671,12 @@ int do_read_index(struct index_state *istate, co= nst char *path, int must_exist) =20 istate->mmap =3D mmap; istate->mmap_size =3D mmap_size; - if (try_shm(istate) && - verify_hdr(istate->mmap, istate->mmap_size) < 0) - goto unmap; + if (try_shm(istate)) { + if (verify_hdr(istate->mmap, istate->mmap_size) < 0) + goto unmap; + } else if (istate->always_verify_trailing_sha1 && + verify_hdr(istate->mmap, istate->mmap_size) < 0) + goto unmap; hdr =3D mmap =3D istate->mmap; mmap_size =3D istate->mmap_size; if (!istate->keep_mmap) --=20 2.4.2.767.g62658d5-twtrsrc