sysdeps/unix/sysv/linux/pidfd_getpid.c

   1 /* pidfd_getpid - Get the associated pid from the pid file descriptor.
   2    Copyright (C) 2023-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <_itoa.h>
  20 #include <errno.h>
  21 #include <intprops.h>
  22 #include <procutils.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <sysdep.h>
  26 #include <unistd.h>
  27
  28 #define FDINFO_TO_FILENAME_PREFIX "/proc/self/fdinfo/"
  29
  30 #define FDINFO_FILENAME_LEN \
  31   (sizeof (FDINFO_TO_FILENAME_PREFIX) + INT_STRLEN_BOUND (int))
  32
  33 struct parse_fdinfo_t
  34 {
  35   bool found;
  36   pid_t pid;
  37 };
  38
  39 /* Parse the PID field in the fdinfo entry, if existent.  Avoid strtol or
  40    similar to not be locale dependent.  */
  41 static int
  42 parse_fdinfo (const char *l, void *arg)
  43 {
  44   enum { fieldlen = sizeof ("Pid:") - 1 };
  45   if (strncmp (l, "Pid:", fieldlen) != 0)
  46     return 0;
  47
  48   l += fieldlen;
  49
  50   /* Skip leading spaces.  */
  51   while (*l == ' ' || (unsigned int) (*l) -'\t' < 5)
  52     l++;
  53
  54   bool neg = false;
  55   switch (*l)
  56     {
  57     case '-':
  58       neg = true;
  59       l++;
  60       break;
  61     case '+':
  62       return -1;
  63     }
  64
  65   if (*l == '\0')
  66     return 0;
  67
  68   int n = 0;
  69   while (*l != '\0')
  70     {
  71       /* Check if '*l' is a digit.  */
  72       if ('0' > *l || *l > '9')
  73         return -1;
  74
  75       /* Ignore invalid large values.  */
  76       if (INT_MULTIPLY_WRAPV (10, n, &n)
  77           || INT_ADD_WRAPV (n, *l++ - '0', &n))
  78         return -1;
  79     }
  80
  81   /* -1 indicates that the process is terminated.  */
  82   if (neg && n != 1)
  83     return -1;
  84
  85   struct parse_fdinfo_t *fdinfo = arg;
  86   fdinfo->pid = neg ? -n : n;
  87   fdinfo->found = true;
  88
  89   return 1;
  90 }
  91
  92 pid_t
  93 pidfd_getpid (int fd)
  94 {
  95   if (__glibc_unlikely (fd < 0))
  96     {
  97       __set_errno (EBADF);
  98       return -1;
  99     }
 100
 101   char fdinfoname[FDINFO_FILENAME_LEN];
 102
 103   char *p = mempcpy (fdinfoname, FDINFO_TO_FILENAME_PREFIX,
 104                      strlen (FDINFO_TO_FILENAME_PREFIX));
 105   *_fitoa_word (fd, p, 10, 0) = '\0';
 106
 107   struct parse_fdinfo_t fdinfo = { .found = false, .pid = -1 };
 108   if (!procutils_read_file (fdinfoname, parse_fdinfo, &fdinfo))
 109     /* The fdinfo contains an invalid 'Pid:' value.  */
 110     return INLINE_SYSCALL_ERROR_RETURN_VALUE (EBADF);
 111
 112   /* The FD does not have a 'Pid:' entry associated.  */
 113   if (!fdinfo.found)
 114     return INLINE_SYSCALL_ERROR_RETURN_VALUE (EBADF);
 115
 116   /* The pidfd cannot be resolved because it is in a separate pid
 117      namespace.  */
 118   if (fdinfo.pid == 0)
 119     return INLINE_SYSCALL_ERROR_RETURN_VALUE (EREMOTE);
 120
 121   /* A negative value means the process is terminated.  */
 122   if (fdinfo.pid < 0)
 123     return INLINE_SYSCALL_ERROR_RETURN_VALUE (ESRCH);
 124
 125   return fdinfo.pid;
 126 }