Subject: [PATCH] connect: also update offset for features without values

From: "Andrzej Hunt via GitGitGadget" <[email-masked]>
Date: Sat, 18 Sep 2021 13:14:32 +0000

From: Andrzej Hunt <[email-masked]>

parse_feature_value() does not update offset if the feature being
searched for does not specify a value. A loop that uses
parse_feature_value() to find a feature which was specified without a
value therefore might never exit (such loops will typically use
next_server_feature_value() as opposed to parse_feature_value() itself).
This usually isn't an issue: there's no point in using
next_server_feature_value() to search for repeated instances of the same
capability unless that capability typically specifies a value - but a
broken server could send a response that omits the value for a feature
even when we are expecting a value.

Therefore we add an offset update calculation for the no-value case,
which helps ensure that loops using next_server_feature_value() will
always terminate.

next_server_feature_value(), and the offset calculation, were first
added in 2.28 in:
  2c6a403d96 (connect: add function to parse multiple v1 capability values, 2020-05-25)

Thanks to Peff for authoring the test.

Co-authored-by: Jeff King <[email-masked]>
Signed-off-by: Jeff King <[email-masked]>
Signed-off-by: Andrzej Hunt <[email-masked]>
---
    connect: also update offset for features without values
    
    This is a small patch to avoid an infinite loop which can occur when a
    broken server forgets to include a value when specifying symref in the
    capabilities list.
    
    Thanks to Peff for writing the test.
    
    Note: I modified the test by adding and object-format=... to the
    injected server response, because the oid that we're using is the
    default hash (which will be e.g. sha256 for some CI jobs), but our
    protocol handler assumes sha1 unless a different hash has been
    explicitly specified. I'm open to alternative suggestions.
    
    ATB,
    
    Andrzej

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1091%2Fahunt%2Fconnectloop-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1091/ahunt/connectloop-v1
Pull-Request: https://github.com/git/git/pull/1091

 connect.c                      |  2 ++
 t/t5704-protocol-violations.sh | 13 +++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/connect.c b/connect.c
index aff13a270e6..eaf7d6d2618 100644
--- a/connect.c
+++ b/connect.c
@@ -557,6 +557,8 @@ const char *parse_feature_value(const char *feature_list, const char *feature, i
 			if (!*value || isspace(*value)) {
 				if (lenp)
 					*lenp = 0;
+				if (offset)
+					*offset = found + len - feature_list;
 				return value;
 			}
 			/* feature with a value (e.g., "agent=git/1.2.3") */
diff --git a/t/t5704-protocol-violations.sh b/t/t5704-protocol-violations.sh
index 5c941949b98..34538cebf01 100755
--- a/t/t5704-protocol-violations.sh
+++ b/t/t5704-protocol-violations.sh
@@ -32,4 +32,17 @@ test_expect_success 'extra delim packet in v2 fetch args' '
 	test_i18ngrep "expected flush after fetch arguments" err
 '
 
+test_expect_success 'bogus symref in v0 capabilities' '
+	test_commit foo &&
+	oid=$(git rev-parse HEAD) &&
+	{
+		printf "%s HEAD\0symref object-format=%s\n" "$oid" "$GIT_DEFAULT_HASH" |
+			test-tool pkt-line pack-raw-stdin &&
+		printf "0000"
+	} >input &&
+	git ls-remote --upload-pack="cat input ;:" . >actual &&
+	printf "%s\tHEAD\n" "$oid" >expect &&
+	test_cmp expect actual
+'
+
 test_done

base-commit: 186eaaae567db501179c0af0bf89b34cbea02c26
-- 
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