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/* pidfd_getpid - Get the associated pid from the pid file descriptor.
Copyright (C) 2023-2024 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <_itoa.h>
#include <errno.h>
#include <intprops.h>
#include <procutils.h>
#include <stdlib.h>
#include <string.h>
#include <sysdep.h>
#include <unistd.h>
#define FDINFO_TO_FILENAME_PREFIX "/proc/self/fdinfo/"
#define FDINFO_FILENAME_LEN \
(sizeof (FDINFO_TO_FILENAME_PREFIX) + INT_STRLEN_BOUND (int))
struct parse_fdinfo_t
{
bool found;
pid_t pid;
};
/* Parse the PID field in the fdinfo entry, if existent. Avoid strtol or
similar to not be locale dependent. */
static int
parse_fdinfo (const char *l, void *arg)
{
enum { fieldlen = sizeof ("Pid:") - 1 };
if (strncmp (l, "Pid:", fieldlen) != 0)
return 0;
l += fieldlen;
/* Skip leading spaces. */
while (*l == ' ' || (unsigned int) (*l) -'\t' < 5)
l++;
bool neg = false;
switch (*l)
{
case '-':
neg = true;
l++;
break;
case '+':
return -1;
}
if (*l == '\0')
return 0;
int n = 0;
while (*l != '\0')
{
/* Check if '*l' is a digit. */
if ('0' > *l || *l > '9')
return -1;
/* Ignore invalid large values. */
if (INT_MULTIPLY_WRAPV (10, n, &n)
|| INT_ADD_WRAPV (n, *l - '0', &n))
return -1;
l++;
}
/* -1 indicates that the process is terminated. */
if (neg && n != 1)
return -1;
struct parse_fdinfo_t *fdinfo = arg;
fdinfo->pid = neg ? -n : n;
fdinfo->found = true;
return 1;
}
pid_t
pidfd_getpid (int fd)
{
if (__glibc_unlikely (fd < 0))
{
__set_errno (EBADF);
return -1;
}
char fdinfoname[FDINFO_FILENAME_LEN];
char *p = mempcpy (fdinfoname, FDINFO_TO_FILENAME_PREFIX,
strlen (FDINFO_TO_FILENAME_PREFIX));
*_fitoa_word (fd, p, 10, 0) = '\0';
struct parse_fdinfo_t fdinfo = { .found = false, .pid = -1 };
if (!procutils_read_file (fdinfoname, parse_fdinfo, &fdinfo))
/* The fdinfo contains an invalid 'Pid:' value. */
return INLINE_SYSCALL_ERROR_RETURN_VALUE (EBADF);
/* The FD does not have a 'Pid:' entry associated. */
if (!fdinfo.found)
return INLINE_SYSCALL_ERROR_RETURN_VALUE (EBADF);
/* The pidfd cannot be resolved because it is in a separate pid
namespace. */
if (fdinfo.pid == 0)
return INLINE_SYSCALL_ERROR_RETURN_VALUE (EREMOTE);
/* A negative value means the process is terminated. */
if (fdinfo.pid < 0)
return INLINE_SYSCALL_ERROR_RETURN_VALUE (ESRCH);
return fdinfo.pid;
}
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