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basic/terminal-util: operate on one fd in get_default_background_color()

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This moves the open call earlier, so that we do any state-changing operations
if we actually managed to open the nonblocking fd. The code is easier to follow
this way and might be more robust.

Suprisingly, this fixes https://github.com/systemd/systemd/issues/39055: it
seems that run0 chowns /dev/stdin (in my case /dev/pts/0) to root:root, and the
second run0 can read and write stdin/stdout throught the already-open fds,
but fd_reopen fails.

Fixes https://github.com/systemd/systemd/issues/39055.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
2025-11-20 14:33:26 +01:00
parent 933c690030
commit 46f6742911
1 changed files with 9 additions and 11 deletions
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20
src/basic/terminal-util.c
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@@ -2260,7 +2260,6 @@ static int scan_background_color_response(
}
int get_default_background_color(double *ret_red, double *ret_green, double *ret_blue) {
_cleanup_close_ int nonblock_input_fd = -EBADF;
int r;
assert(ret_red);
@@ -2280,27 +2279,26 @@ int get_default_background_color(double *ret_red, double *ret_green, double *ret
return 0;
}
/* Open a 2nd input fd, in non-blocking mode, so that we won't ever hang in read()
* should someone else process the POLLIN. Do all subsequent operations on the new fd. */
_cleanup_close_ int nonblock_input_fd = r = fd_reopen(STDIN_FILENO, O_RDONLY|O_CLOEXEC|O_NONBLOCK|O_NOCTTY);
if (r < 0)
return r;
struct termios old_termios;
if (tcgetattr(STDIN_FILENO, &old_termios) < 0)
if (tcgetattr(nonblock_input_fd, &old_termios) < 0)
return -errno;
struct termios new_termios = old_termios;
termios_disable_echo(&new_termios);
if (tcsetattr(STDIN_FILENO, TCSANOW, &new_termios) < 0)
if (tcsetattr(nonblock_input_fd, TCSANOW, &new_termios) < 0)
return -errno;
r = loop_write(STDOUT_FILENO, ANSI_OSC "11;?" ANSI_ST, SIZE_MAX);
if (r < 0)
goto finish;
/* Open a 2nd input fd, in non-blocking mode, so that we won't ever hang in read() should someone
* else process the POLLIN. */
nonblock_input_fd = r = fd_reopen(STDIN_FILENO, O_RDONLY|O_CLOEXEC|O_NONBLOCK|O_NOCTTY);
if (r < 0)
goto finish;
usec_t end = usec_add(now(CLOCK_MONOTONIC), CONSOLE_REPLY_WAIT_USEC);
char buf[STRLEN(ANSI_OSC "11;rgb:0/0/0" ANSI_ST)]; /* shortest possible reply */
size_t buf_full = 0;
@@ -2359,7 +2357,7 @@ int get_default_background_color(double *ret_red, double *ret_green, double *ret
}
finish:
RET_GATHER(r, RET_NERRNO(tcsetattr(STDIN_FILENO, TCSANOW, &old_termios)));
RET_GATHER(r, RET_NERRNO(tcsetattr(nonblock_input_fd, TCSANOW, &old_termios)));
return r;
}