Re: [PATCH 1/3] wincred: ignore unknown lines (do not die)
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Sep 22, 2022, 21:19 UTC
- Message-ID
- <xmqqbkr7xg28.fsf@gitster.g>
- In-Reply-To
- <6426f9c3954866b3fd9259d1a58d2c41dc42e17f.1663865974.git.gitgitgadget@gmail.com>
"Matthew John Cheetham via GitGitGadget" <gitgitgadget@gmail.com> writes:
Show 5 quoted lines
> From: Matthew John Cheetham <mjcheetham@outlook.com> > > It is the expectation that credential helpers be liberal in what they > accept and conservative in what they return, to allow for future growth > and evolution of the protocol/interaction.
That is nice in principle, and the updated code below may work well with existing "other side of the connection" (codepaths in "git" that asks credential API to talk to the helpers), but I am not sure if this is always a safe thing to do.
When we gain a new "command" in the protocol, if we just read it without understanding it, would we open ourselves to a risk of breaking the protocol communication, worst of which may be to deadlock? A new command, when received by a more recent helper that understands how to react to it, may _require_ it to write more than "username" and "password" back to "git" from get_credential(), for example, but the helper with this patch alone, while not complaining about seeing such a new and unknown command, would not know how to compute and write that third thing other than "username" and "password"---would the other side who issued that new command get stuck waiting for us to return the third thing? Worse yet, the new command may expect us to read further in get_credential() (e.g. maybe they will give us a challenge, which may need to be used when yielding the "username" and "password" things), but because we do not even know we need to read, their attempt to write to us may get them stuck, and that is when we are expecting to write to them, easily leading to a deadlock, no?
> All of the other helpers (store, cache, osxkeychain, libsecret, > gnome-keyring) except `netrc` currently ignore any credential lines > that are not recognised, whereas the Windows helper (wincred) instead > dies.
Is that different from saying "everybody other than netrc and win ignore unknown"?
> Fix the discrepancy and ignore unknown lines in the wincred helper.
OK. As long as everybody consistently ignores, and possibly opens themselves up consistently to a protocol mismatch issue, it is OK. We will know if that can be a real problem or does not happen in practice.
Show 22 quoted lines
> Signed-off-by: Matthew John Cheetham <mjcheetham@outlook.com>
> ---
> contrib/credential/wincred/git-credential-wincred.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/contrib/credential/wincred/git-credential-wincred.c b/contrib/credential/wincred/git-credential-wincred.c
> index 5091048f9c6..ead6e267c78 100644
> --- a/contrib/credential/wincred/git-credential-wincred.c
> +++ b/contrib/credential/wincred/git-credential-wincred.c
> @@ -278,8 +278,11 @@ static void read_credential(void)
> wusername = utf8_to_utf16_dup(v);
> } else if (!strcmp(buf, "password"))
> password = utf8_to_utf16_dup(v);
> - else
> - die("unrecognized input");
> + /*
> + * Ignore other lines; we don't know what they mean, but
> + * this future-proofs us when later versions of git do
> + * learn new lines, and the helpers are updated to match.
> + */
> }
> }