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LibC: Don't rely on ptsname and ttyname syscalls

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Instead, to determine these values (both the pts name and tty name), use
other methods. For determining the new name of the allocated psuedo
terminal, use ioctl on a file descriptor we got after opening /dev/ptmx
with the TIOCGPTN option.
For determining the name of TTY, we enumerate both /dev/pts and /dev
directories to find matching inode number and matching device mode.
This commit is contained in:
Liav A 2022-02-15 21:39:01 +02:00 • committed by Andreas Kling
parent 5ffe2f117c
commit de7566c2c4
2 changed files with 103 additions and 4 deletions
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38
Userland/Libraries/LibC/stdlib.cpp
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@ -24,8 +24,11 @@
#include <stdlib.h>
#include <string.h>
#include <sys/internals.h>
#include <sys/ioctl.h>
#include <sys/ioctl_numbers.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
#include <sys/wait.h>
#include <syscall.h>
#include <unistd.h>
@ -724,8 +727,39 @@ char* ptsname(int fd)
int ptsname_r(int fd, char* buffer, size_t size)
{
int rc = syscall(SC_ptsname, fd, buffer, size);
__RETURN_WITH_ERRNO(rc, rc, -1);
struct stat stat;
if (fstat(fd, &stat) < 0)
return -1;
StringBuilder devpts_path_builder;
devpts_path_builder.append("/dev/pts/"sv);
int master_pty_index = 0;
// Note: When the user opens a PTY from /dev/ptmx with posix_openpt(), the open file descriptor
// points to /dev/ptmx, (major number is 5 and minor number is 2), but internally
// in the kernel, it points to a new MasterPTY device. When we do ioctl with TIOCGPTN option
// on the open file descriptor, it actually asks the MasterPTY what is the assigned index
// of it when the PTYMultiplexer created it.
if (ioctl(fd, TIOCGPTN, &master_pty_index) < 0)
return -1;
if (master_pty_index < 0) {
errno = EINVAL;
return -1;
}
devpts_path_builder.appendff("{:d}", master_pty_index);
if (devpts_path_builder.length() > size) {
errno = ERANGE;
return -1;
}
memset(buffer, 0, devpts_path_builder.length() + 1);
auto full_devpts_path_string = devpts_path_builder.build();
if (!full_devpts_path_string.copy_characters_to_buffer(buffer, size)) {
errno = ERANGE;
return -1;
}
return 0;
}
static unsigned long s_next_rand = 1;