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From: "Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
To: git@vger.kernel.org
Cc: Johannes Sixt <j6t@kdbg.org>,
	Johannes Schindelin <johannes.schindelin@gmx.de>,
	Junio C Hamano <gitster@pobox.com>,
	Johannes Schindelin <johannes.schindelin@gmx.de>
Subject: [PATCH 1/1] mingw: do set `errno` correctly when trying to restrict handle inheritance
Date: Fri, 29 Nov 2019 21:44:36 +0000
Message-ID: <685360f735e35e837bc9ef684cbde33564c81666.1575063876.git.gitgitgadget@gmail.com> (raw)
In-Reply-To: <pull.480.git.1575063876.gitgitgadget@gmail.com>

From: Johannes Schindelin <johannes.schindelin@gmx.de>

In 9a780a384de (mingw: spawned processes need to inherit only standard
handles, 2019-11-22), we taught the Windows-specific part to restrict
which file handles are passed on to the spawned processes.

Since this logic seemed to be a bit fragile across Windows versions (we
_still_ support Windows Vista in Git for Windows, for example), a
fall-back was added to try spawning the process again, this time without
restricting which file handles are to be inherited by the spawned
process.

In the common case (i.e. when the process could not be spawned for
reasons _other_ than the file handle inheritance), the fall-back attempt
would still fail, of course.

Crucially, one thing we missed in that code path was to set `errno`
appropriately.

This should have been caught by t0061.2 which expected `errno` to be
`ENOENT` after trying to start a process for a non-existing executable,
but `errno` was set to `ENOENT` prior to the `CreateProcessW()` call:
while looking for the config settings for trace2, Git tries to access
`xdg_config` and `user_config` via `access_or_die()`, and as neither of
those config files exists when running the test case (because in Git's
test suite, `HOME` points to the test directory), the `errno` has the
expected value, but for the wrong reasons.

Let's fix that by making sure that `errno` is set correctly.

It would be nice if we could somehow fix t0061 to make sure that this
does not regress again. One approach that seemed like it should work,
but did not, was to set `errno` to 0 in the test helper that is used by
t0061.2.

However, when `mingw_spawnvpe()` wants to see whether the file in
question is a script, it calls `parse_interpreter()`, which in turn
tries to `open()` the file.0/compat/mingw.c#L1134. Obviously,
this call fails, and sets `errno` to `ENOENT`, deep inside the call
chain started from that test helper.

Instead, we force re-set `errno` at the beginning of the function
`mingw_spawnve_fd()`, which _should_ be safe given that callers of that
function will want to look at `errno` if -1 was returned. And if that
`errno` is 0 ("No error"), regression tests like t0061.2 will kick in.

Reported-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 compat/mingw.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/compat/mingw.c b/compat/mingw.c
index 2b6eca2f56..bb4eb4211a 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -1423,6 +1423,9 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
 	const char *(*quote_arg)(const char *arg) =
 		is_msys2_sh(*argv) ? quote_arg_msys2 : quote_arg_msvc;
 
+	/* Make sure to override previous errors, if any */
+	errno = 0;
+
 	if (restrict_handle_inheritance < 0)
 		restrict_handle_inheritance = core_restrict_inherited_handles;
 	/*
@@ -1580,8 +1583,8 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
 		ret = CreateProcessW(*wcmd ? wcmd : NULL, wargs, NULL, NULL,
 				     TRUE, flags, wenvblk, dir ? wdir : NULL,
 				     &si.StartupInfo, &pi);
+		errno = err_win_to_posix(GetLastError());
 		if (ret && buf.len) {
-			errno = err_win_to_posix(GetLastError());
 			warning("failed to restrict file handles (%ld)\n\n%s",
 				err, buf.buf);
 		}
-- 
gitgitgadget

  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-29 21:44 [PATCH 0/1] Brown-bag fix on top of js/mingw-inherit-only-std-handles Johannes Schindelin via GitGitGadget
2019-11-29 21:44 ` Johannes Schindelin via GitGitGadget [this message]
2019-11-29 23:02   ` [PATCH 1/1] mingw: do set `errno` correctly when trying to restrict handle inheritance Johannes Sixt
2019-11-30 22:06     ` Johannes Schindelin
2019-11-30 22:16       ` Johannes Sixt
2019-11-30 10:36 ` [PATCH v2 0/2] Brown-bag fix on top of js/mingw-inherit-only-std-handles Johannes Schindelin via GitGitGadget
2019-11-30 10:36   ` [PATCH v2 1/2] mingw: do set `errno` correctly when trying to restrict handle inheritance Johannes Schindelin via GitGitGadget
2019-11-30 10:36   ` [PATCH v2 2/2] mingw: translate ERROR_SUCCESS to errno = 0 Johannes Schindelin via GitGitGadget
2019-11-30 18:04   ` [PATCH v2 0/2] Brown-bag fix on top of js/mingw-inherit-only-std-handles Junio C Hamano
2019-11-30 19:13     ` Johannes Sixt
2019-11-30 20:11       ` Andreas Schwab
2019-11-30 20:23         ` Junio C Hamano
2019-11-30 20:43           ` Andreas Schwab
2019-11-30 21:22             ` Johannes Schindelin
2019-11-30 20:21       ` Junio C Hamano
2019-12-01  6:26         ` Junio C Hamano
2019-12-01  9:53           ` Johannes Schindelin
2019-12-02  6:07             ` Junio C Hamano
2019-12-02  9:05               ` Johannes Schindelin
2019-11-30 19:20   ` Johannes Sixt
2019-11-30 22:09     ` Junio C Hamano
2019-12-02 11:33   ` [PATCH v3 " Johannes Schindelin via GitGitGadget
2019-12-02 11:33     ` [PATCH v3 1/2] mingw: do set `errno` correctly when trying to restrict handle inheritance Johannes Schindelin via GitGitGadget
2019-12-02 11:33     ` [PATCH v3 2/2] mingw: translate ERROR_SUCCESS to errno = 0 Johannes Schindelin via GitGitGadget
2019-12-02 17:35     ` [PATCH v3 0/2] Brown-bag fix on top of js/mingw-inherit-only-std-handles Johannes Sixt
2019-12-02 19:04       ` Junio C Hamano
2019-12-03 12:04       ` Johannes Schindelin

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