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Replace home-env patches with the upstreamed ones #63

Merged
merged 7 commits into from
Jul 9, 2024
Merged

Replace home-env patches with the upstreamed ones #63

merged 7 commits into from
Jul 9, 2024

Commits on Jul 9, 2024

  1. fixup! Allow overriding the home directory via the HOME variable 

    In preparation for integrating the patches that made it upstream via
https://inbox.sourceware.org/cygwin-patches/[email protected]/,
let's revert the original patches from Git for Windows' branch thicket.

This reverts commit 81a0e5d.

Signed-off-by: Johannes Schindelin <[email protected]>
    @dscho
    dscho committed Jul 9, 2024
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  2. fixup! Respect db_home setting even for the SYSTEM account 

    In preparation for integrating the patches that made it upstream via
https://inbox.sourceware.org/cygwin-patches/[email protected]/,
let's revert the original patches from Git for Windows' branch thicket.

This reverts commit 22854f6.

Signed-off-by: Johannes Schindelin <[email protected]>
    @dscho
    dscho committed Jul 9, 2024
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  3. fixup! Respect the db_home: env setting under more circumstances 

    In preparation for integrating the patches that made it upstream via
https://inbox.sourceware.org/cygwin-patches/[email protected]/,
let's revert the original patches from Git for Windows' branch thicket.

This reverts commit f0d5641.

Signed-off-by: Johannes Schindelin <[email protected]>
    @dscho
    dscho committed Jul 9, 2024
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  4. Allow deriving the current user's home directory via the HOME variable 

    This patch hails from Git for Windows (where the Cygwin runtime is used
in the form of a slightly modified MSYS2 runtime), where it is a
well-established technique to let the `$HOME` variable define where the
current user's home directory is, falling back to `$HOMEDRIVE$HOMEPATH`
and `$USERPROFILE`.

The idea is that we want to share user-specific settings between
programs, whether they be Cygwin, MSYS2 or not.  Unfortunately, we
cannot blindly activate the "db_home: windows" setting because in some
setups, the user's home directory is set to a hidden directory via an
UNC path (\\share\some\hidden\folder$) -- something many programs
cannot handle correctly, e.g. `cmd.exe` and other native Windows
applications that users want to employ as Git helpers.

The established technique is to allow setting the user's home directory
via the environment variables mentioned above: `$HOMEDRIVE$HOMEPATH` or
`$USERPROFILE`.  This has the additional advantage that it is much
faster than querying the Windows user database.

Of course this scheme needs to be opt-in.  For that reason, it needs
to be activated explicitly via `db_home: env` in `/etc/nsswitch.conf`.

Signed-off-by: Johannes Schindelin <[email protected]>
    @dscho
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  5. Respect db_home setting even for SYSTEM/Microsoft accounts 

    We should not blindly set the home directory of the SYSTEM account (or
of Microsoft accounts) to `/home/<name>`, especially
`/etc/nsswitch.conf` defines `db_home: env`, in which case we want to
respect the `HOME` variable.

Signed-off-by: Johannes Schindelin <[email protected]>
    @dscho
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  6. uinfo: special-case IIS APPPOOL accounts 

    The account under which Azure Web Apps run is an IIS APPOOL account that
is generated on the fly.

These are special because the virtual machines on which thes Apps run
are not domain-joined, yet the accounts are domain accounts.

To support the use case where such a Web App needs to call `ssh` (e.g.
to deploy from a Git repository that is accessible only via SSH), we do
need OpenSSH's `getpwuid (getuid ())` invocation to work.

But currently it does not. Concretely, `getuid ()` returns -1 for these
accounts, and OpenSSH fails to find the correct home directory
(_especially_ when that home directory was overridden via a `db_home:
env` line in `/etc/nsswitch.conf`).

This can be verified e.g. in a Kudu console (for details about Kudu
consoles, see https://github.com/projectkudu/kudu/wiki/Kudu-console):
the domain is `IIS APPPOOL`, the account name is the name of the Azure
Web App, the SID starts with 'S-1-5-82-`, and
`pwdgrp::fetch_account_from_windows()` runs into the code path where
"[...] the domain returned by LookupAccountSid is not our machine name,
and if our machine is no domain member, we lose.  We have nobody to ask
for the POSIX offset."

Since these IIS APPPOOL accounts are relatively similar to AzureAD
accounts in this scenario, let's imitate the latter to support also the
former.

Reported-by: David Ebbo <[email protected]>
Helped-by: Corinna Vinschen <[email protected]>
Signed-off-by: Johannes Schindelin <[email protected]>
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  7. Do not rely on getenv ("HOME")'s path conversion 

    In the very early code path where `dll_crt0_1 ()` calls
`user_shared->initialize ()`, the Cygwin runtime calls `internal_pwsid ()`
to initialize the user name in preparation for reading the `fstab` file.

In case `db_home: env` is defined in `/etc/nsswitch.conf`, we need to
look at the environment variable `HOME` and use it, if set.

When all of this happens, though, the `pinfo_init ()` function has had no
chance to run yet (and therefore, `environ_init ()`). At this stage,
therefore, `getenv ()`'s `findenv_func ()` call still finds `getearly ()`
and we get the _verbatim_ value of `HOME`. That is, the Windows form.
But we need the "POSIX" form.

To add insult to injury, later calls to `getpwuid (getuid ())` will
receive a cached version of the home directory via
`cygheap->pg.pwd_cache.win.find_user ()` thanks to the first
`internal_pwsid ()` call caching the result via
`add_user_from_cygserver ()`, read: we will never receive the converted
`HOME` but always the Windows variant.

So, contrary to the assumptions made in 27376c6 (Allow deriving the
current user's home directory via the HOME variable, 2023-03-28), we
cannot assume that `getenv ("HOME")` returned a "POSIX" path.

This is a real problem. Even setting aside that common callers of
`getpwuid ()` (such as OpenSSH) are unable to handle Windows paths in the
`pw_dir` attribute, the Windows path never makes it back to the caller
unscathed. The value returned from `fetch_home_env ()` is not actually
used as-is. Instead, the `fetch_account_from_windows ()` method uses it
to write a pseudo `/etc/passwd`-formatted line that is _then_ parsed via
the `pwdgrp::parse_passwd ()` method which sees no problem with
misinterpreting the colon after the drive letter as a field separator of
that `/etc/passwd`-formatted line, and instead of a Windows path, we now
have a mere drive letter.

Let's detect when the `HOME` value is still in Windows format in
`fetch_home_env ()`, and convert it in that case.

For good measure, interpret this "Windows format" not only to include
absolute paths with drive prefixes, but also UNC paths.

Signed-off-by: Johannes Schindelin <[email protected]>
    @dscho
    dscho committed Jul 9, 2024
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