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From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: "Carlo Marcelo Arenas Belón" <carenas@gmail.com>
Cc: git@vger.kernel.org, gitster@pobox.com, bagasdotme@gmail.com,
	phillip.wood123@gmail.com, "Guy Maurel" <guy.j@maurel.de>,
	"SZEDER Gábor" <szeder.dev@gmail.com>,
	"Randall Becker" <rsbecker@nexbridge.com>
Subject: Re: [PATCH v3 2/3] git-compat-util: avoid failing dir ownership checks if running privileged
Date: Thu, 5 May 2022 16:01:21 +0200 (CEST)	[thread overview]
Message-ID: <nycvar.QRO.7.76.6.2205051545370.355@tvgsbejvaqbjf.bet> (raw)
In-Reply-To: <20220503065442.95699-3-carenas@gmail.com>

[-- Attachment #1: Type: text/plain, Size: 5560 bytes --]

Hi Carlo,

On Mon, 2 May 2022, Carlo Marcelo Arenas Belón wrote:

> bdc77d1d685 (Add a function to determine whether a path is owned by the
> current user, 2022-03-02) checks for the effective uid of the running
> process using geteuid() but didn't account for cases where that user was
> root (because git was invoked through sudo or a compatible tool) and the
> original uid that repository trusted for its config was no longer known,
> therefore failing the following otherwise safe call:
>
>   guy@renard ~/Software/uncrustify $ sudo git describe --always --dirty
>   [sudo] password for guy:
>   fatal: unsafe repository ('/home/guy/Software/uncrustify' is owned by someone else)
>
> Attempt to detect those cases by using the environment variables that
> those tools create to keep track of the original user id, and do the
> ownership check using that instead.
>
> This assumes the environment the user is running on after going
> privileged can't be tampered with, and also adds code to restrict that
> the new behavior only applies if running as root, therefore keeping the
> most common case, which runs unprivileged, from changing, but because of
> that, it will miss cases where sudo (or an equivalent) was used to change
> to another unprivileged user or where the equivalent tool used to raise
> privileges didn't track the original id in a sudo compatible way.

Hmm. I do realize that this is a quite common scenario, and I wish we
would not need to rush for a fix here: Otherwise we could carefully design
an "untrusted" mode in which Git errors out on spawning user-specified
commands and on writing files (and avoids refreshing the index to avoid
having to write a file), but runs normally if none of that is needed.

> diff --git a/Documentation/config/safe.txt b/Documentation/config/safe.txt
> index 6d764fe0ccf..ee558ced8c7 100644
> --- a/Documentation/config/safe.txt
> +++ b/Documentation/config/safe.txt
> @@ -26,3 +26,12 @@ directory was listed in the `safe.directory` list. If `safe.directory=*`
>  is set in system config and you want to re-enable this protection, then
>  initialize your list with an empty value before listing the repositories
>  that you deem safe.
> ++
> +When git tries to check for ownership of git repositories, it will
> +obviously do so with the uid of the user that is running git itself,
> +but if git is running as root, it will check first if it might have
> +been started through `sudo`, and if that is the case, will instead
> +use the uid of the user that did so.
> +If that is not what you would prefer and want git to only trust
> +repositories that are owned by root instead, then you should remove
> +the `SUDO_UID` variable from root's environment.
> diff --git a/git-compat-util.h b/git-compat-util.h
> index 63ba89dd31d..dfdd3e4f81a 100644
> --- a/git-compat-util.h
> +++ b/git-compat-util.h
> @@ -393,12 +393,50 @@ static inline int git_offset_1st_component(const char *path)
>  #endif
>
>  #ifndef is_path_owned_by_current_user
> +
> +#ifdef __TANDEM
> +#define ROOT_UID 65535
> +#else
> +#define ROOT_UID 0
> +#endif

I do wonder whether we have to play this kind of fragile game. Why not
simply respect `SUDO_UID` if it is set? It's not like we expect attackers
to have control over the environment and could set this malicously.

> +
> +/*
> + * this helper function overrides a ROOT_UID with the one provided by
> + * an environment variable, do not use unless the original user is
> + * root
> + */
> +static inline void extract_id_from_env(const char *env, uid_t *id)
> +{
> +	const char *real_uid = getenv(env);
> +
> +	/* discard any empty values */
> +	if (real_uid && *real_uid) {
> +		char *endptr;
> +		unsigned long env_id;
> +		int saved_errno = errno;
> +
> +		errno = 0;
> +		env_id = strtoul(real_uid, &endptr, 10);
> +		if (!errno && !*endptr && env_id <= (uid_t)-1)

We should not look at `errno` here unless the return value of `strtoul()`
indicates that there might have been an error (i.e. when it is
`ULONG_MAX`).

Likewise, we need to either initialize `endptr` or only look at it when
`strtoul()` succeeded.

We could side-step all of this, of course, if we simply did this:

	euid = getuid();
	if (euid == ROOT_UID)
		euid = git_env_ulong("SUDO_UID", euid);

> +			*id = env_id;
> +
> +		errno = saved_errno;
> +	}

> +}
> +
>  static inline int is_path_owned_by_current_uid(const char *path)
>  {
>  	struct stat st;
> +	uid_t euid;
> +
>  	if (lstat(path, &st))
>  		return 0;
> -	return st.st_uid == geteuid();
> +
> +	euid = geteuid();
> +	if (euid == ROOT_UID)
> +		extract_id_from_env("SUDO_UID", &euid);
> +
> +	return st.st_uid == euid;

Since this code is not even compiled on Windows, I believe we need to
adjust the documentation accordingly ("On systems other than Windows,
where `sudo` is available, ...").

>  }
>
>  #define is_path_owned_by_current_user is_path_owned_by_current_uid
> diff --git a/t/t0034-root-safe-directory.sh b/t/t0034-root-safe-directory.sh
> index 6dac7a05cfd..dd659aed4e1 100755
> --- a/t/t0034-root-safe-directory.sh
> +++ b/t/t0034-root-safe-directory.sh
> @@ -32,7 +32,7 @@ test_expect_success SUDO 'setup' '
>  	)
>  '
>
> -test_expect_failure SUDO 'sudo git status as original owner' '
> +test_expect_success SUDO 'sudo git status as original owner' '
>  	(
>  		cd root/r &&
>  		git status &&
> --
> 2.36.0.352.g0cd7feaf86f

Again, thank you for working on this!
Dscho

  reply	other threads:[~2022-05-05 14:01 UTC|newest]

Thread overview: 170+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-26 18:31 [RFC PATCH] git-compat-util: avoid failing dir ownership checks if running priviledged Carlo Marcelo Arenas Belón
2022-04-26 19:48 ` Derrick Stolee
2022-04-26 19:56   ` Junio C Hamano
2022-04-26 20:10     ` rsbecker
2022-04-26 20:45       ` Carlo Arenas
2022-04-26 21:10         ` Junio C Hamano
2022-04-26 20:12     ` Carlo Arenas
2022-04-26 20:26   ` Carlo Arenas
2022-04-29 16:16   ` Derrick Stolee
2022-04-27  0:05 ` [PATCH] git-compat-util: avoid failing dir ownership checks if running privileged Carlo Marcelo Arenas Belón
2022-04-27  9:33   ` Phillip Wood
2022-04-27 12:30     ` Phillip Wood
2022-04-27 14:15       ` rsbecker
2022-04-27 15:58       ` Carlo Arenas
2022-04-27 16:14         ` Phillip Wood
2022-04-27 18:54           ` Junio C Hamano
2022-04-27 20:59             ` Carlo Arenas
2022-04-27 21:09               ` rsbecker
2022-04-27 21:25               ` Junio C Hamano
2022-04-28 17:56             ` Phillip Wood
2022-04-27 15:38     ` Carlo Arenas
2022-04-27 15:50       ` rsbecker
2022-04-27 16:19       ` Junio C Hamano
2022-04-27 16:45         ` Carlo Arenas
2022-04-27 17:22         ` Phillip Wood
2022-04-27 17:49           ` rsbecker
2022-04-27 17:54             ` Carlo Arenas
2022-04-27 18:05               ` rsbecker
2022-04-27 18:11                 ` Carlo Arenas
2022-04-27 18:16                   ` rsbecker
2022-04-27 16:31       ` Phillip Wood
2022-04-27 16:54         ` Carlo Arenas
2022-04-27 17:28           ` Phillip Wood
2022-04-27 17:49             ` Carlo Arenas
2022-04-27 22:26   ` [RFC PATCH v2] " Carlo Marcelo Arenas Belón
2022-04-27 22:33     ` Junio C Hamano
2022-04-28  3:35     ` [PATCH 0/2] fix `sudo make install` regression in maint Carlo Marcelo Arenas Belón
2022-04-28  3:35       ` [PATCH 1/2] Documentation: explain how safe.directory works when running under sudo Carlo Marcelo Arenas Belón
2022-04-28  5:17         ` Junio C Hamano
2022-04-28  5:58           ` Carlo Arenas
2022-04-28  6:41             ` Junio C Hamano
2022-04-28  3:35       ` [PATCH 2/2] t: add tests for safe.directory when running with sudo Carlo Marcelo Arenas Belón
2022-04-28  5:34         ` Junio C Hamano
2022-04-28  4:57       ` [PATCH 0/2] fix `sudo make install` regression in maint Junio C Hamano
2022-04-28 10:58       ` [PATCH v2 0/3] " Carlo Marcelo Arenas Belón
2022-04-28 10:58         ` [PATCH v2 1/3] git-compat-util: avoid failing dir ownership checks if running privileged Carlo Marcelo Arenas Belón
2022-04-28 18:02           ` Phillip Wood
2022-04-28 18:57             ` Carlo Arenas
2022-04-28 10:58         ` [PATCH v2 2/3] Documentation: explain how safe.directory works when running under sudo Carlo Marcelo Arenas Belón
2022-04-30  6:17           ` Bagas Sanjaya
2022-04-30  6:39             ` Junio C Hamano
2022-04-30 14:15             ` Carlo Marcelo Arenas Belón
2022-04-28 10:58         ` [PATCH v2 3/3] t: add tests for safe.directory when running with sudo Carlo Marcelo Arenas Belón
2022-04-28 16:55           ` Junio C Hamano
2022-04-28 18:08             ` Phillip Wood
2022-04-28 18:12               ` Junio C Hamano
2022-05-06 17:50                 ` Carlo Arenas
2022-05-06 21:43                   ` Junio C Hamano
2022-05-06 22:57                     ` Carlo Arenas
2022-05-06 23:55                       ` Junio C Hamano
2022-05-07 11:57                         ` Carlo Marcelo Arenas Belón
2022-04-28 19:53             ` rsbecker
2022-04-28 20:22               ` Carlo Arenas
2022-04-28 20:43                 ` rsbecker
2022-04-28 20:51                   ` Junio C Hamano
2022-04-28 20:56                   ` Carlo Arenas
2022-04-28 21:55                     ` rsbecker
2022-04-28 22:21                       ` Junio C Hamano
2022-04-28 22:45                         ` rsbecker
2022-04-28 20:46                 ` Junio C Hamano
2022-04-28 20:32               ` Junio C Hamano
2022-04-28 20:40                 ` rsbecker
2022-04-28 20:48                 ` Carlo Arenas
2022-04-28 21:02             ` Carlo Arenas
2022-04-28 21:07               ` Junio C Hamano
2022-04-29  1:24                 ` Carlo Marcelo Arenas Belón
2022-04-29 18:50                   ` Junio C Hamano
2022-04-29 20:05                     ` Carlo Marcelo Arenas Belón
2022-05-02 18:39         ` [RFC PATCH v3 0/3] fix `sudo make install` regression in maint Carlo Marcelo Arenas Belón
2022-05-02 18:39           ` [RFC PATCH v3 1/3] t: document regression git safe.directory when using sudo Carlo Marcelo Arenas Belón
2022-05-02 21:35             ` Junio C Hamano
2022-05-02 23:07               ` Carlo Arenas
2022-05-02 18:39           ` [RFC PATCH v3 2/3] git-compat-util: avoid failing dir ownership checks if running privileged Carlo Marcelo Arenas Belón
2022-05-02 18:39           ` [RFC PATCH v3 3/3] t0034: enhance framework to allow testing more commands under sudo Carlo Marcelo Arenas Belón
2022-05-02 22:10             ` Junio C Hamano
2022-05-03  0:00               ` Carlo Arenas
2022-05-03  6:54         ` [PATCH v3 0/3] fix `sudo make install` regression in maint Carlo Marcelo Arenas Belón
2022-05-03  6:54           ` [PATCH v3 1/3] t: document regression git safe.directory when using sudo Carlo Marcelo Arenas Belón
2022-05-03 14:03             ` Phillip Wood
2022-05-03 15:56               ` Carlo Marcelo Arenas Belón
2022-05-04 11:15                 ` Phillip Wood
2022-05-04 13:02                   ` Carlo Arenas
2022-05-04 14:11                     ` Phillip Wood
2022-05-05 13:44             ` Johannes Schindelin
2022-05-05 14:34               ` Phillip Wood
2022-05-05 15:50               ` Junio C Hamano
2022-05-05 18:33               ` Junio C Hamano
2022-05-05 19:39                 ` Junio C Hamano
2022-05-06 21:03                   ` Carlo Arenas
2022-05-09  8:21                 ` Phillip Wood
2022-05-09 14:51                   ` Carlo Arenas
2022-05-09 15:18                     ` Phillip Wood
2022-05-09 16:01                   ` Junio C Hamano
2022-05-09 16:21                     ` Carlo Arenas
2022-05-06 17:39               ` Carlo Arenas
2022-05-03  6:54           ` [PATCH v3 2/3] git-compat-util: avoid failing dir ownership checks if running privileged Carlo Marcelo Arenas Belón
2022-05-05 14:01             ` Johannes Schindelin [this message]
2022-05-05 14:32               ` Phillip Wood
2022-05-06 19:15                 ` Carlo Arenas
2022-05-06 20:00                   ` Junio C Hamano
2022-05-06 20:22                     ` Carlo Arenas
2022-05-06 20:59                       ` Junio C Hamano
2022-05-06 21:40                         ` Carlo Arenas
2022-05-06 21:07                       ` rsbecker
2022-05-05 16:09               ` Junio C Hamano
2022-05-06 20:02               ` Carlo Arenas
2022-05-03  6:54           ` [PATCH v3 3/3] t0034: enhance framework to allow testing more commands under sudo Carlo Marcelo Arenas Belón
2022-05-03 14:12             ` Phillip Wood
2022-05-03 15:27               ` Junio C Hamano
2022-05-06 16:54               ` Carlo Arenas
2022-05-07 16:35           ` [RFC PATCH v4 0/3] fix `sudo make install` regression in maint Carlo Marcelo Arenas Belón
2022-05-07 16:35             ` [RFC PATCH v4 1/3] t: regression git needs safe.directory when using sudo Carlo Marcelo Arenas Belón
2022-05-07 16:35             ` [RFC PATCH v4 2/3] git-compat-util: avoid failing dir ownership checks if running privileged Carlo Marcelo Arenas Belón
2022-05-07 17:34               ` Junio C Hamano
2022-05-07 18:56                 ` Carlo Marcelo Arenas Belón
2022-05-09 16:54                   ` Junio C Hamano
2022-05-09 17:36                     ` rsbecker
2022-05-09 18:48                     ` Carlo Arenas
2022-05-09 19:16                       ` rsbecker
2022-05-09 19:41                       ` Junio C Hamano
2022-05-07 16:35             ` [RFC PATCH v4 3/3] t0034: add negative tests and allow git init to mostly work under sudo Carlo Marcelo Arenas Belón
2022-05-10 14:17             ` [RFC PATCH v4 0/3] fix `sudo make install` regression in maint Phillip Wood
2022-05-10 15:47               ` Carlo Arenas
2022-05-10 17:46             ` [PATCH " Carlo Marcelo Arenas Belón
2022-05-10 17:46               ` [PATCH v4 1/3] t: regression git needs safe.directory when using sudo Carlo Marcelo Arenas Belón
2022-05-10 22:10                 ` Junio C Hamano
2022-05-10 23:11                   ` Carlo Arenas
2022-05-10 23:44                     ` Junio C Hamano
2022-05-11  0:56                       ` Carlo Arenas
2022-05-11  1:11                         ` Junio C Hamano
2022-05-10 17:46               ` [PATCH v4 2/3] git-compat-util: avoid failing dir ownership checks if running privileged Carlo Marcelo Arenas Belón
2022-05-10 22:57                 ` Junio C Hamano
2022-05-11  7:34                   ` Carlo Arenas
2022-05-11 14:58                     ` Junio C Hamano
2022-05-10 17:46               ` [PATCH v4 3/3] t0034: add negative tests and allow git init to mostly work under sudo Carlo Marcelo Arenas Belón
2022-05-10 23:11                 ` Junio C Hamano
2022-05-10 23:25                   ` Junio C Hamano
2022-05-11 14:04                   ` Carlo Arenas
2022-05-11 15:29                     ` Junio C Hamano
2022-05-13  1:00               ` [PATCH v5 0/4] fix `sudo make install` regression in maint Carlo Marcelo Arenas Belón
2022-05-13  1:00                 ` [PATCH v5 1/4] t: regression git needs safe.directory when using sudo Carlo Marcelo Arenas Belón
2022-06-03 12:12                   ` SZEDER Gábor
2022-05-13  1:00                 ` [PATCH v5 2/4] git-compat-util: avoid failing dir ownership checks if running privileged Carlo Marcelo Arenas Belón
2022-06-03 11:05                   ` SZEDER Gábor
2022-06-03 16:54                     ` Junio C Hamano
2022-06-03 17:34                       ` SZEDER Gábor
2022-05-13  1:00                 ` [PATCH v5 3/4] t0034: add negative tests and allow git init to mostly work under sudo Carlo Marcelo Arenas Belón
2022-05-13  1:20                   ` Junio C Hamano
2022-05-14 14:36                     ` Carlo Arenas
2022-05-15 16:54                       ` Junio C Hamano
2022-05-15 19:21                         ` Carlo Arenas
2022-05-16  5:27                           ` Junio C Hamano
2022-05-16 13:07                             ` Carlo Marcelo Arenas Belón
2022-05-16 16:25                               ` Junio C Hamano
2022-05-13  1:00                 ` [PATCH v5 4/4] git-compat-util: allow root to access both SUDO_UID and root owned Carlo Marcelo Arenas Belón
2022-06-15 14:02                   ` Johannes Schindelin
2022-06-17 14:26                     ` Carlo Arenas
2022-06-17 16:00                       ` Junio C Hamano
2022-06-17 20:23                   ` [PATCH v6] " Carlo Marcelo Arenas Belón
2022-06-17 21:02                     ` Junio C Hamano

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