1/* Create /proc/self/fd-related names for subfiles of open directories. 2 3 Copyright (C) 2006, 2009-2022 Free Software Foundation, Inc. 4 5 This program is free software: you can redistribute it and/or modify 6 it under the terms of the GNU General Public License as published by 7 the Free Software Foundation, either version 3 of the License, or 8 (at your option) any later version. 9 10 This program 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 13 GNU General Public License for more details. 14 15 You should have received a copy of the GNU General Public License 16 along with this program. If not, see <https://www.gnu.org/licenses/>. */ 17 18/* Written by Paul Eggert. */ 19 20#include <config.h> 21 22#include "openat-priv.h" 23 24#include <sys/types.h> 25#include <sys/stat.h> 26#include <fcntl.h> 27 28#include <stdio.h> 29#include <stdlib.h> 30#include <string.h> 31#include <unistd.h> 32 33#ifdef __KLIBC__ 34# include <InnoTekLIBC/backend.h> 35#endif 36 37#include "intprops.h" 38 39/* Set BUF to the name of the subfile of the directory identified by 40 FD, where the subfile is named FILE. If successful, return BUF if 41 the result fits in BUF, dynamically allocated memory otherwise. 42 Return NULL (setting errno) on error. */ 43char * 44openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file) 45{ 46 char *result = buf; 47 int dirlen; 48 49 /* Make sure the caller gets ENOENT when appropriate. */ 50 if (!*file) 51 { 52 buf[0] = '\0'; 53 return buf; 54 } 55 56#ifndef __KLIBC__ 57# define PROC_SELF_FD_FORMAT "/proc/self/fd/%d/" 58 { 59 enum { 60 PROC_SELF_FD_DIR_SIZE_BOUND 61 = (sizeof PROC_SELF_FD_FORMAT - (sizeof "%d" - 1) 62 + INT_STRLEN_BOUND (int)) 63 }; 64 65 static int proc_status = 0; 66 if (! proc_status) 67 { 68 /* Set PROC_STATUS to a positive value if /proc/self/fd is 69 reliable, and a negative value otherwise. Solaris 10 70 /proc/self/fd mishandles "..", and any file name might expand 71 to ".." after symbolic link expansion, so avoid /proc/self/fd 72 if it mishandles "..". Solaris 10 has openat, but this 73 problem is exhibited on code that built on Solaris 8 and 74 running on Solaris 10. */ 75 76 int proc_self_fd = 77 open ("/proc/self/fd", 78 O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NONBLOCK | O_CLOEXEC); 79 if (proc_self_fd < 0) 80 proc_status = -1; 81 else 82 { 83 /* Detect whether /proc/self/fd/%i/../fd exists, where %i is the 84 number of a file descriptor open on /proc/self/fd. On Linux, 85 that name resolves to /proc/self/fd, which was opened above. 86 However, on Solaris, it may resolve to /proc/self/fd/fd, which 87 cannot exist, since all names in /proc/self/fd are numeric. */ 88 char dotdot_buf[PROC_SELF_FD_DIR_SIZE_BOUND + sizeof "../fd" - 1]; 89 sprintf (dotdot_buf, PROC_SELF_FD_FORMAT "../fd", proc_self_fd); 90 proc_status = access (dotdot_buf, F_OK) ? -1 : 1; 91 close (proc_self_fd); 92 } 93 } 94 95 if (proc_status < 0) 96 return NULL; 97 else 98 { 99 size_t bufsize = PROC_SELF_FD_DIR_SIZE_BOUND + strlen (file); 100 if (OPENAT_BUFFER_SIZE < bufsize) 101 { 102 result = malloc (bufsize); 103 if (! result) 104 return NULL; 105 } 106 107 dirlen = sprintf (result, PROC_SELF_FD_FORMAT, fd); 108 } 109 } 110#else 111 /* OS/2 kLIBC provides a function to retrieve a path from a fd. */ 112 { 113 char dir[_MAX_PATH]; 114 size_t bufsize; 115 116 if (__libc_Back_ioFHToPath (fd, dir, sizeof dir)) 117 return NULL; 118 119 dirlen = strlen (dir); 120 bufsize = dirlen + 1 + strlen (file) + 1; /* 1 for '/', 1 for null */ 121 if (OPENAT_BUFFER_SIZE < bufsize) 122 { 123 result = malloc (bufsize); 124 if (! result) 125 return NULL; 126 } 127 128 strcpy (result, dir); 129 result[dirlen++] = '/'; 130 } 131#endif 132 133 strcpy (result + dirlen, file); 134 return result; 135} 136