@matheusbsbs / matheus-bagliano / commits / ae9abbb63e

git-compat-util: avoid failing dir ownership checks if running privileged

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. Because of compatibility with sudo, the code assumes that uid_t is an unsigned integer type (which is not required by the standard) but is used that way in their codebase to generate SUDO_UID. In systems where uid_t is signed, sudo might be also patched to NOT be unsigned and that might be able to trigger an edge case and a bug (as described in the code), but it is considered unlikely to happen and even if it does, the code would just mostly fail safely, so there was no attempt either to detect it or prevent it by the code, which is something that might change in the future, based on expected user feedback. Reported-by: Guy Maurel <guy.j@maurel.de> Helped-by: SZEDER Gábor <szeder.dev@gmail.com> Helped-by: Randall Becker <rsbecker@nexbridge.com> Helped-by: Phillip Wood <phillip.wood123@gmail.com> Suggested-by: Johannes Schindelin <Johannes.Schindelin@gmx.de> Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Carlo Marcelo Arenas Belón committed May 12, 2022 at 18:00 UTC ae9abbb63eea74441e3e8b153dc6ec1f94c373b4

3 files changed +66 -2

Documentation/config/safe.txt

+13

@@ -26,3 +26,16 @@ directory was listed in the `safe.directory` list. If `safe.directory=*`

26 is set in system config and you want to re-enable this protection, then

27 initialize your list with an empty value before listing the repositories

28 that you deem safe.

29 ++

30 +As explained, Git only allows you to access repositories owned by

31 +yourself, i.e. the user who is running Git, by default. When Git

32 +is running as 'root' in a non Windows platform that provides sudo,

33 + however, git checks the SUDO_UID environment variable that sudo creates

34 +and will allow access to the uid recorded as its value instead.

35 +This is to make it easy to perform a common sequence during installation

36 +"make && sudo make install". A git process running under 'sudo' runs as

37 +'root' but the 'sudo' command exports the environment variable to record

38 +which id the original user has.

39 +If that is not what you would prefer and want git to only trust

40 +repositories that are owned by root instead, then you must remove

41 +the `SUDO_UID` variable from root's environment before invoking git.

git-compat-util.h

+52 -1

@@ -393,12 +393,63 @@ static inline int git_offset_1st_component(const char *path)

393 #endif

394

395 #ifndef is_path_owned_by_current_user

396 +

397 +#ifdef __TANDEM

398 +#define ROOT_UID 65535

399 +#else

400 +#define ROOT_UID 0

401 +#endif

402 +

403 +/*

404 + * Do not use this function when

405 + * (1) geteuid() did not say we are running as 'root', or

406 + * (2) using this function will compromise the system.

407 + *

408 + * PORTABILITY WARNING:

409 + * This code assumes uid_t is unsigned because that is what sudo does.

410 + * If your uid_t type is signed and all your ids are positive then it

411 + * should all work fine.

412 + * If your version of sudo uses negative values for uid_t or it is

413 + * buggy and return an overflowed value in SUDO_UID, then git might

414 + * fail to grant access to your repository properly or even mistakenly

415 + * grant access to someone else.

416 + * In the unlikely scenario this happened to you, and that is how you

417 + * got to this message, we would like to know about it; so sent us an

418 + * email to git@vger.kernel.org indicating which platform you are

419 + * using and which version of sudo, so we can improve this logic and

420 + * maybe provide you with a patch that would prevent this issue again

421 + * in the future.

422 + */

423 +static inline void extract_id_from_env(const char *env, uid_t *id)

424 +{

425 + const char *real_uid = getenv(env);

426 +

427 + /* discard anything empty to avoid a more complex check below */

428 + if (real_uid && *real_uid) {

429 + char *endptr = NULL;

430 + unsigned long env_id;

431 +

432 + errno = 0;

433 + /* silent overflow errors could trigger a bug here */

434 + env_id = strtoul(real_uid, &endptr, 10);

435 + if (!*endptr && !errno)

436 + *id = env_id;

437 + }

438 +}

439 +

440 static inline int is_path_owned_by_current_uid(const char *path)

441 {

442 struct stat st;

443 + uid_t euid;

444 +

445 if (lstat(path, &st))

446 return 0;

401 - return st.st_uid == geteuid();

447 +

448 + euid = geteuid();

449 + if (euid == ROOT_UID)

450 + extract_id_from_env("SUDO_UID", &euid);

451 +

452 + return st.st_uid == euid;

453 }

454

455 #define is_path_owned_by_current_user is_path_owned_by_current_uid

t/t0034-root-safe-directory.sh

+1 -1

@@ -28,7 +28,7 @@ test_expect_success SUDO 'setup' '

28 )

29 '

31 -test_expect_failure SUDO 'sudo git status as original owner' '

31 +test_expect_success SUDO 'sudo git status as original owner' '

32 (

33 cd root/r &&

34 git status &&