From 9a6bbee8006c24b46a85d29e7b38cfa79e9ab21b Mon Sep 17 00:00:00 2001 From: Jeff King Date: Wed, 11 Mar 2020 17:53:41 -0400 Subject: [PATCH 1/5] credential: avoid writing values with newlines The credential protocol that we use to speak to helpers can't represent values with newlines in them. This was an intentional design choice to keep the protocol simple, since none of the values we pass should generally have newlines. However, if we _do_ encounter a newline in a value, we blindly transmit it in credential_write(). Such values may break the protocol syntax, or worse, inject new valid lines into the protocol stream. The most likely way for a newline to end up in a credential struct is by decoding a URL with a percent-encoded newline. However, since the bug occurs at the moment we write the value to the protocol, we'll catch it there. That should leave no possibility of accidentally missing a code path that can trigger the problem. At this level of the code we have little choice but to die(). However, since we'd not ever expect to see this case outside of a malicious URL, that's an acceptable outcome. Reported-by: Felix Wilhelm --- credential.c | 2 ++ t/t0300-credentials.sh | 6 ++++++ 2 files changed, 8 insertions(+) diff --git a/credential.c b/credential.c index 9747f47b18..00ee4d62db 100644 --- a/credential.c +++ b/credential.c @@ -194,6 +194,8 @@ static void credential_write_item(FILE *fp, const char *key, const char *value) { if (!value) return; + if (strchr(value, '\n')) + die("credential value for %s contains newline", key); fprintf(fp, "%s=%s\n", key, value); } diff --git a/t/t0300-credentials.sh b/t/t0300-credentials.sh index 03bd31e9f2..15cc3c5abb 100755 --- a/t/t0300-credentials.sh +++ b/t/t0300-credentials.sh @@ -309,4 +309,10 @@ test_expect_success 'empty helper spec resets helper list' ' EOF ' +test_expect_success 'url parser rejects embedded newlines' ' + test_must_fail git credential fill <<-\EOF + url=https://one.example.com?%0ahost=two.example.com/ + EOF +' + test_done From 17f1c0b8c7e447aa62f85dc355bb48133d2812f2 Mon Sep 17 00:00:00 2001 From: Jeff King Date: Wed, 11 Mar 2020 18:11:37 -0400 Subject: [PATCH 2/5] t/lib-credential: use test_i18ncmp to check stderr The credential tests have a "check" function which feeds some input to git-credential and checks the stdout and stderr. We look for exact matches in the output. For stdout, this makes sense; the output is the credential protocol. But for stderr, we may be showing various diagnostic messages, or the prompts fed to the askpass program, which could be translated. Let's mark them as such. --- t/lib-credential.sh | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/t/lib-credential.sh b/t/lib-credential.sh index 937b831ea6..bb88cc0108 100755 --- a/t/lib-credential.sh +++ b/t/lib-credential.sh @@ -19,7 +19,7 @@ check() { false fi && test_cmp expect-stdout stdout && - test_cmp expect-stderr stderr + test_i18ncmp expect-stderr stderr } read_chunk() { From c716fe4bd917e013bf376a678b3a924447777b2d Mon Sep 17 00:00:00 2001 From: Jeff King Date: Thu, 12 Mar 2020 01:31:11 -0400 Subject: [PATCH 3/5] credential: detect unrepresentable values when parsing urls The credential protocol can't represent newlines in values, but URLs can embed percent-encoded newlines in various components. A previous commit taught the low-level writing routines to die() when encountering this, but we can be a little friendlier to the user by detecting them earlier and handling them gracefully. This patch teaches credential_from_url() to notice such components, issue a warning, and blank the credential (which will generally result in prompting the user for a username and password). We blank the whole credential in this case. Another option would be to blank only the invalid component. However, we're probably better off not feeding a partially-parsed URL result to a credential helper. We don't know how a given helper would handle it, so we're better off to err on the side of matching nothing rather than something unexpected. The die() call in credential_write() is _probably_ impossible to reach after this patch. Values should end up in credential structs only by URL parsing (which is covered here), or by reading credential protocol input (which by definition cannot read a newline into a value). But we should definitely keep the low-level check, as it's our final and most accurate line of defense against protocol injection attacks. Arguably it could become a BUG(), but it probably doesn't matter much either way. Note that the public interface of credential_from_url() grows a little more than we need here. We'll use the extra flexibility in a future patch to help fsck catch these cases. --- credential.c | 36 ++++++++++++++++++++++++++++++++++-- credential.h | 16 ++++++++++++++++ t/t0300-credentials.sh | 12 ++++++++++-- 3 files changed, 60 insertions(+), 4 deletions(-) diff --git a/credential.c b/credential.c index 00ee4d62db..eeeac3242e 100644 --- a/credential.c +++ b/credential.c @@ -321,7 +321,22 @@ void credential_reject(struct credential *c) c->approved = 0; } -void credential_from_url(struct credential *c, const char *url) +static int check_url_component(const char *url, int quiet, + const char *name, const char *value) +{ + if (!value) + return 0; + if (!strchr(value, '\n')) + return 0; + + if (!quiet) + warning(_("url contains a newline in its %s component: %s"), + name, url); + return -1; +} + +int credential_from_url_gently(struct credential *c, const char *url, + int quiet) { const char *at, *colon, *cp, *slash, *host, *proto_end; @@ -335,7 +350,7 @@ void credential_from_url(struct credential *c, const char *url) */ proto_end = strstr(url, "://"); if (!proto_end) - return; + return 0; cp = proto_end + 3; at = strchr(cp, '@'); colon = strchr(cp, ':'); @@ -370,4 +385,21 @@ void credential_from_url(struct credential *c, const char *url) while (p > c->path && *p == '/') *p-- = '\0'; } + + if (check_url_component(url, quiet, "username", c->username) < 0 || + check_url_component(url, quiet, "password", c->password) < 0 || + check_url_component(url, quiet, "protocol", c->protocol) < 0 || + check_url_component(url, quiet, "host", c->host) < 0 || + check_url_component(url, quiet, "path", c->path) < 0) + return -1; + + return 0; +} + +void credential_from_url(struct credential *c, const char *url) +{ + if (credential_from_url_gently(c, url, 0) < 0) { + warning(_("skipping credential lookup for url: %s"), url); + credential_clear(c); + } } diff --git a/credential.h b/credential.h index 6b0cd16be2..122a23cd2f 100644 --- a/credential.h +++ b/credential.h @@ -28,7 +28,23 @@ void credential_reject(struct credential *); int credential_read(struct credential *, FILE *); void credential_write(const struct credential *, FILE *); + +/* + * Parse a url into a credential struct, replacing any existing contents. + * + * Ifthe url can't be parsed (e.g., a missing "proto://" component), the + * resulting credential will be empty but we'll still return success from the + * "gently" form. + * + * If we encounter a component which cannot be represented as a credential + * value (e.g., because it contains a newline), the "gently" form will return + * an error but leave the broken state in the credential object for further + * examination. The non-gentle form will issue a warning to stderr and return + * an empty credential. + */ void credential_from_url(struct credential *, const char *url); +int credential_from_url_gently(struct credential *, const char *url, int quiet); + int credential_match(const struct credential *have, const struct credential *want); diff --git a/t/t0300-credentials.sh b/t/t0300-credentials.sh index 15cc3c5abb..3bec445cac 100755 --- a/t/t0300-credentials.sh +++ b/t/t0300-credentials.sh @@ -309,9 +309,17 @@ test_expect_success 'empty helper spec resets helper list' ' EOF ' -test_expect_success 'url parser rejects embedded newlines' ' - test_must_fail git credential fill <<-\EOF +test_expect_success 'url parser ignores embedded newlines' ' + check fill <<-EOF url=https://one.example.com?%0ahost=two.example.com/ + -- + username=askpass-username + password=askpass-password + -- + warning: url contains a newline in its host component: https://one.example.com?%0ahost=two.example.com/ + warning: skipping credential lookup for url: https://one.example.com?%0ahost=two.example.com/ + askpass: Username: + askpass: Password: EOF ' From 07259e74ec1237c836874342c65650bdee8a3993 Mon Sep 17 00:00:00 2001 From: Jeff King Date: Wed, 11 Mar 2020 18:48:24 -0400 Subject: [PATCH 4/5] fsck: detect gitmodules URLs with embedded newlines The credential protocol can't handle values with newlines. We already detect and block any such URLs from being used with credential helpers, but let's also add an fsck check to detect and block gitmodules files with such URLs. That will let us notice the problem earlier when transfer.fsckObjects is turned on. And in particular it will prevent bad objects from spreading, which may protect downstream users running older versions of Git. We'll file this under the existing gitmodulesUrl flag, which covers URLs with option injection. There's really no need to distinguish the exact flaw in the URL in this context. Likewise, I've expanded the description of t7416 to cover all types of bogus URLs. --- fsck.c | 16 +++++++++++++++- t/t7416-submodule-dash-url.sh | 18 +++++++++++++++++- 2 files changed, 32 insertions(+), 2 deletions(-) diff --git a/fsck.c b/fsck.c index 0741e62586..5b437c260c 100644 --- a/fsck.c +++ b/fsck.c @@ -14,6 +14,7 @@ #include "packfile.h" #include "submodule-config.h" #include "config.h" +#include "credential.h" static struct oidset gitmodules_found = OIDSET_INIT; static struct oidset gitmodules_done = OIDSET_INIT; @@ -941,6 +942,19 @@ static int fsck_tag(struct tag *tag, const char *data, return fsck_tag_buffer(tag, data, size, options); } +static int check_submodule_url(const char *url) +{ + struct credential c = CREDENTIAL_INIT; + int ret; + + if (looks_like_command_line_option(url)) + return -1; + + ret = credential_from_url_gently(&c, url, 1); + credential_clear(&c); + return ret; +} + struct fsck_gitmodules_data { struct object *obj; struct fsck_options *options; @@ -965,7 +979,7 @@ static int fsck_gitmodules_fn(const char *var, const char *value, void *vdata) "disallowed submodule name: %s", name); if (!strcmp(key, "url") && value && - looks_like_command_line_option(value)) + check_submodule_url(value) < 0) data->ret |= report(data->options, data->obj, FSCK_MSG_GITMODULES_URL, "disallowed submodule url: %s", diff --git a/t/t7416-submodule-dash-url.sh b/t/t7416-submodule-dash-url.sh index 5ba041f537..41431b1ac3 100755 --- a/t/t7416-submodule-dash-url.sh +++ b/t/t7416-submodule-dash-url.sh @@ -1,6 +1,6 @@ #!/bin/sh -test_description='check handling of .gitmodule url with dash' +test_description='check handling of disallowed .gitmodule urls' . ./test-lib.sh test_expect_success 'create submodule with protected dash in url' ' @@ -60,4 +60,20 @@ test_expect_success 'trailing backslash is handled correctly' ' test_i18ngrep ! "unknown option" err ' +test_expect_success 'fsck rejects embedded newline in url' ' + # create an orphan branch to avoid existing .gitmodules objects + git checkout --orphan newline && + cat >.gitmodules <<-\EOF && + [submodule "foo"] + url = "https://one.example.com?%0ahost=two.example.com/foo.git" + EOF + git add .gitmodules && + git commit -m "gitmodules with newline" && + test_when_finished "rm -rf dst" && + git init --bare dst && + git -C dst config transfer.fsckObjects true && + test_must_fail git push dst HEAD 2>err && + grep gitmodulesUrl err +' + test_done From c42c0f12972194564f039dcf580d89ca14ae72d6 Mon Sep 17 00:00:00 2001 From: Junio C Hamano Date: Tue, 17 Mar 2020 13:23:48 -0700 Subject: [PATCH 5/5] Git 2.17.4 Signed-off-by: Junio C Hamano --- Documentation/RelNotes/2.17.4.txt | 16 ++++++++++++++++ GIT-VERSION-GEN | 2 +- RelNotes | 2 +- 3 files changed, 18 insertions(+), 2 deletions(-) create mode 100644 Documentation/RelNotes/2.17.4.txt diff --git a/Documentation/RelNotes/2.17.4.txt b/Documentation/RelNotes/2.17.4.txt new file mode 100644 index 0000000000..7d794ca01a --- /dev/null +++ b/Documentation/RelNotes/2.17.4.txt @@ -0,0 +1,16 @@ +Git v2.17.4 Release Notes +========================= + +This release is to address the security issue: CVE-2020-5260 + +Fixes since v2.17.3 +------------------- + + * With a crafted URL that contains a newline in it, the credential + helper machinery can be fooled to give credential information for + a wrong host. The attack has been made impossible by forbidding + a newline character in any value passed via the credential + protocol. + +Credit for finding the vulnerability goes to Felix Wilhelm of Google +Project Zero. diff --git a/GIT-VERSION-GEN b/GIT-VERSION-GEN index bd6cd16e3d..cdb21b3311 100755 --- a/GIT-VERSION-GEN +++ b/GIT-VERSION-GEN @@ -1,7 +1,7 @@ #!/bin/sh GVF=GIT-VERSION-FILE -DEF_VER=v2.17.3 +DEF_VER=v2.17.4 LF=' ' diff --git a/RelNotes b/RelNotes index d14bdb5eda..196ab8077e 120000 --- a/RelNotes +++ b/RelNotes @@ -1 +1 @@ -Documentation/RelNotes/2.17.3.txt \ No newline at end of file +Documentation/RelNotes/2.17.4.txt \ No newline at end of file