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gspawn: Report errors with closing file descriptors between fork/exec

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If a seccomp policy is set up incorrectly so that it returns `EPERM` for
`close_range()` rather than `ENOSYS` due to it not being recognised, no
error would previously be reported from GLib, but some file descriptors
wouldn’t be closed, and that would cause a hung zombie process. The
zombie process would be waiting for one half of a socket to be closed.

Fix that by correctly propagating errors from `close_range()` back to the
parent process so they can be reported correctly.

Distributions which aren’t yet carrying the Docker fix to correctly
return `ENOSYS` from unrecognised syscalls may want to temporarily carry
an additional patch to fall back to `safe_fdwalk()` if `close_range()`
fails with `EPERM`. This change will not be accepted upstream as `EPERM`
is not the right error for `close_range()` to be returning.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

Fixes: #2580
This commit is contained in:
Philip Withnall 2022-01-17 15:27:24 +00:00
parent a7a5b24f86
commit ce04a12404
1 changed files with 31 additions and 13 deletions
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44
glib/gspawn.c
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@ -1520,7 +1520,7 @@ safe_fdwalk (int (*cb)(void *data, int fd), void *data)
/* This function is called between fork() and exec() and hence must be
* async-signal-safe (see signal-safety(7)). */
static void
static int
safe_fdwalk_set_cloexec (int lowfd)
{
#if defined(HAVE_CLOSE_RANGE) && defined(CLOSE_RANGE_CLOEXEC)
@ -1534,15 +1534,18 @@ safe_fdwalk_set_cloexec (int lowfd)
* Handle ENOSYS in case it’s supported in libc but not the kernel; if so,
* fall back to safe_fdwalk(). Handle EINVAL in case `CLOSE_RANGE_CLOEXEC`
* is not supported. */
if (close_range (lowfd, G_MAXUINT, CLOSE_RANGE_CLOEXEC) != 0 &&
(errno == ENOSYS || errno == EINVAL))
int ret = close_range (lowfd, G_MAXUINT, CLOSE_RANGE_CLOEXEC);
if (ret == 0 || !(errno == ENOSYS || errno == EINVAL))
return ret;
#endif /* HAVE_CLOSE_RANGE */
(void) safe_fdwalk (set_cloexec, GINT_TO_POINTER (lowfd));
return safe_fdwalk (set_cloexec, GINT_TO_POINTER (lowfd));
}
/* This function is called between fork() and exec() and hence must be
* async-signal-safe (see signal-safety(7)). */
static void
* async-signal-safe (see signal-safety(7)).
*
* On failure, `-1` will be returned and errno will be set. */
static int
safe_closefrom (int lowfd)
{
#if defined(__FreeBSD__) || defined(__OpenBSD__) || \
@ -1560,6 +1563,7 @@ safe_closefrom (int lowfd)
* On such systems, F_CLOSEFROM is defined.
*/
(void) closefrom (lowfd);
return 0;
#elif defined(__DragonFly__)
/* It is unclear whether closefrom function included in DragonFlyBSD libc_r
* is safe to use because it calls a lot of library functions. It is also
@ -1567,12 +1571,13 @@ safe_closefrom (int lowfd)
* direct system call here ourselves to avoid possible issues.
*/
(void) syscall (SYS_closefrom, lowfd);
return 0;
#elif defined(F_CLOSEM)
/* NetBSD and AIX have a special fcntl command which does the same thing as
* closefrom. NetBSD also includes closefrom function, which seems to be a
* simple wrapper of the fcntl command.
*/
(void) fcntl (lowfd, F_CLOSEM);
return fcntl (lowfd, F_CLOSEM);
#else
#if defined(HAVE_CLOSE_RANGE)
@ -1582,9 +1587,11 @@ safe_closefrom (int lowfd)
*
* Handle ENOSYS in case it’s supported in libc but not the kernel; if so,
* fall back to safe_fdwalk(). */
if (close_range (lowfd, G_MAXUINT, 0) != 0 && errno == ENOSYS)
int ret = close_range (lowfd, G_MAXUINT, 0);
if (ret == 0 || errno != ENOSYS)
return ret;
#endif /* HAVE_CLOSE_RANGE */
(void) safe_fdwalk (close_func, GINT_TO_POINTER (lowfd));
return safe_fdwalk (close_func, GINT_TO_POINTER (lowfd));
#endif
}
@ -1622,7 +1629,8 @@ enum
CHILD_EXEC_FAILED,
CHILD_OPEN_FAILED,
CHILD_DUP2_FAILED,
CHILD_FORK_FAILED
CHILD_FORK_FAILED,
CHILD_CLOSE_FAILED,
};
/* This function is called between fork() and exec() and hence must be
@ -1738,12 +1746,14 @@ do_exec (gint child_err_report_fd,
if (safe_dup2 (child_err_report_fd, 3) < 0)
write_err_and_exit (child_err_report_fd, CHILD_DUP2_FAILED);
set_cloexec (GINT_TO_POINTER (0), 3);
safe_closefrom (4);
if (safe_closefrom (4) < 0)
write_err_and_exit (child_err_report_fd, CHILD_CLOSE_FAILED);
child_err_report_fd = 3;
}
else
{
safe_fdwalk_set_cloexec (3);
if (safe_fdwalk_set_cloexec (3) < 0)
write_err_and_exit (child_err_report_fd, CHILD_CLOSE_FAILED);
}
}
else
@ -2543,7 +2553,15 @@ fork_exec (gboolean intermediate_child,
_("Failed to fork child process (%s)"),
g_strerror (buf[1]));
break;
case CHILD_CLOSE_FAILED:
g_set_error (error,
G_SPAWN_ERROR,
G_SPAWN_ERROR_FAILED,
_("Failed to close file descriptor for child process (%s)"),
g_strerror (buf[1]));
break;
default:
g_set_error (error,
G_SPAWN_ERROR,