From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Turner Subject: [PATCH v2 04/17] index-helper: add --strict Date: Fri, 18 Mar 2016 21:04:37 -0400 Message-ID: <1458349490-1704-5-git-send-email-dturner@twopensource.com> References: <1458349490-1704-1-git-send-email-dturner@twopensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE To: git@vger.kernel.org, pclouds@gmail.com, Johannes Schindelin X-From: git-owner@vger.kernel.org Sat Mar 19 02:06:25 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 1ah5LU-0008I6-2z for gcvg-git-2@plane.gmane.org; Sat, 19 Mar 2016 02:06:24 +0100 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754177AbcCSBGT convert rfc822-to-quoted-printable (ORCPT ); Fri, 18 Mar 2016 21:06:19 -0400 Received: from mail-qk0-f176.google.com ([209.85.220.176]:33648 "EHLO mail-qk0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754080AbcCSBGL (ORCPT ); Fri, 18 Mar 2016 21:06:11 -0400 Received: by mail-qk0-f176.google.com with SMTP id s5so56377803qkd.0 for ; Fri, 18 Mar 2016 18:06:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=twopensource-com.20150623.gappssmtp.com; s=20150623; h=from:to:subject:date:message-id:in-reply-to:references:mime-version :content-transfer-encoding; bh=CuU/W2k6zD4okOZAMBrnvAOUX6zrBE+22Sy8bGvxjLA=; b=mHuzoSsLFwTcAX05QfYLwrLvrsBlTg/yvVr2FMiPMmgXKvWyPOjNdiwLbCu3Xv0yJX rAhVj4iOuhzQ69EqF+b+A8zF68YMIU6lTSXBBEdavLZQzYOYyggtw4lM39vpRd6RJFLF ivGw1twR9GDt4lZ37MwVymI1RKMt0RxLMh4ANAPK1O4KuFzpmPY4MhWqDk4GqyvNg2fB bCYYMxaHocgX4LtexGFLPGtDO1CYRN8b35U6/7kKqNKPwWZ6GGrmFYIDzgRg1c3jDCon GlXwffhPIcIHu1/OTo8Ntu1FWP/xj5OiCW0BrU63JPJWNANVl27iv0mjVw2pqMc+79Hj /m+A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=CuU/W2k6zD4okOZAMBrnvAOUX6zrBE+22Sy8bGvxjLA=; b=ZXOpGrOAm47PxMiy5ueGgb+oT3wcDjrrKmcYCqwCivljmFX0+zLppBd1o6S12dBTFq f4P611q9fvX+py9ItOeY/Hy8xuiSVeDyQ+5HClIRQV9HUKUaiD47BBQ7QzB0KCkeSICw 8APteHKHENH26JrXTsP6wmWg5GYiujrYvpBvukhT8TXyAFp9kbxee4MmIH7KIso67xUN m5kNvm+985DcSMl5RB8ShU5wYuldCZLTEpitKdFyu8IuPwZbGbApCAeGZenpeXIv0Mx6 mPBy8cxbqdUtmdq8b1+hRdS0FumjuiPdhqK5eBl5KtwUb2UKzC9fMPFQjBGVf3HTQ84o ZYsQ== X-Gm-Message-State: AD7BkJJLRvodYAYkDtK7ew2RsHN6ppKtu6s1+fDfgE4qbzQ048cjZMvOUcgJoFe5mtqYPA== X-Received: by 10.55.74.141 with SMTP id x135mr25903677qka.20.1458349569992; Fri, 18 Mar 2016 18:06:09 -0700 (PDT) Received: from ubuntu.twitter.corp? ([8.25.196.26]) by smtp.gmail.com with ESMTPSA id 139sm7186154qho.2.2016.03.18.18.06.08 (version=TLSv1/SSLv3 cipher=OTHER); Fri, 18 Mar 2016 18:06:09 -0700 (PDT) X-Mailer: git-send-email 2.4.2.767.g62658d5-twtrsrc In-Reply-To: <1458349490-1704-1-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 --- 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 59a5abc..7afc5c9 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 `` minutes. Specify 0 to wait forever. Default is 10. =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 ----- $GIT_DIR/index-helper.pipe is a named pipe that the daemon reads diff --git a/cache.h b/cache.h index c3c6d85..5805962 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 962c973..8d221e0 100644 --- a/index-helper.c +++ b/index-helper.c @@ -15,6 +15,7 @@ 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) { @@ -73,11 +74,56 @@ static void share_index(struct index_state *istate,= 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 @@ -189,6 +235,8 @@ 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 f5fafd6..fe73828 100644 --- a/read-cache.c +++ b/read-cache.c @@ -1648,9 +1648,12 @@ 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