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serve: reject bogus v2 "command=ls-refs=foo"

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When we see a line from the client like "command=ls-refs", we parse
everything after the equals sign as a capability, which we check against
our capabilities table. If we don't recognize the command (e.g.,
"command=foo"), we'll reject it.

But in parse_command(), we use the same get_capability() parser for
parsing non-command lines. So if we see "command=ls-refs=foo", we will
feed "ls-refs=foo" to get_capability(), which will say "OK, that's
ls-refs, with value 'foo'". But then we simply ignore the value
entirely.

The client is violating the spec here, which says:

      command = PKT-LINE("command=" key LF)
      key = 1*(ALPHA | DIGIT | "-_")

I.e., the key is not even allowed to have an equals sign in it. Whereas
a real non-command capability does allow a value:

      capability = PKT-LINE(key[=value] LF)

So by reusing the same get_capability() parser, we are mixing up the
"key" and "capability" tokens. However, since that parser tells us
whether it saw an "=", we can still use it; we just need to reject any
input that produces a non-NULL value field.

The current behavior isn't really hurting anything (the client should
never send such a request, and if it does, we just ignore the "value"
part). But since it does violate the spec, let's tighten it up to
prevent any surprising behavior.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2021-09-15 14:36:33 -04:00 committed by Junio C Hamano
parent 9db5fb4fb3
commit 108c265f27
2 changed files with 11 additions and 1 deletions
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2
serve.c
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@ -220,7 +220,7 @@ static int parse_command(const char *key, struct protocol_capability **command)
if (*command)
die("command '%s' requested after already requesting command '%s'",
out, (*command)->name);
if (!cmd || !cmd->advertise(the_repository, NULL) || !cmd->command)
if (!cmd || !cmd->advertise(the_repository, NULL) || !cmd->command || value)
die("invalid command '%s'", out);
*command = cmd;

10
t/t5701-git-serve.sh
View file

@ -72,6 +72,16 @@ test_expect_success 'request invalid command' '
test_i18ngrep "invalid command" err
'
test_expect_success 'requested command is command=value' '
test-tool pkt-line pack >in <<-EOF &&
command=ls-refs=whatever
object-format=$(test_oid algo)
0000
EOF
test_must_fail test-tool serve-v2 --stateless-rpc 2>err <in &&
grep invalid.command.*ls-refs=whatever err
'
test_expect_success 'wrong object-format' '
test-tool pkt-line pack >in <<-EOF &&
command=fetch