1 /* Create /proc/self/fd-related names for subfiles of open directories. 2 3 Copyright (C) 2006, 2009-2015 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 <http://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 #include "intprops.h" 34 35 #define PROC_SELF_FD_FORMAT "/proc/self/fd/%d/%s" 36 37 #define PROC_SELF_FD_NAME_SIZE_BOUND(len) \ 38 (sizeof PROC_SELF_FD_FORMAT - sizeof "%d%s" \ 39 + INT_STRLEN_BOUND (int) + (len) + 1) 40 41 42 /* Set BUF to the expansion of PROC_SELF_FD_FORMAT, using FD and FILE 43 respectively for %d and %s. If successful, return BUF if the 44 result fits in BUF, dynamically allocated memory otherwise. But 45 return NULL if /proc is not reliable, either because the operating 46 system support is lacking or because memory is low. */ 47 char * 48 openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file) 49 { 50 static int proc_status = 0; 51 52 /* Make sure the caller gets ENOENT when appropriate. */ 53 if (!*file) 54 { 55 buf[0] = '\0'; 56 return buf; 57 } 58 59 if (! proc_status) 60 { 61 /* Set PROC_STATUS to a positive value if /proc/self/fd is 62 reliable, and a negative value otherwise. Solaris 10 63 /proc/self/fd mishandles "..", and any file name might expand 64 to ".." after symbolic link expansion, so avoid /proc/self/fd 65 if it mishandles "..". Solaris 10 has openat, but this 66 problem is exhibited on code that built on Solaris 8 and 67 running on Solaris 10. */ 68 69 int proc_self_fd = open ("/proc/self/fd", 70 O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NONBLOCK); 71 if (proc_self_fd < 0) 72 proc_status = -1; 73 else 74 { 75 /* Detect whether /proc/self/fd/%i/../fd exists, where %i is the 76 number of a file descriptor open on /proc/self/fd. On Linux, 77 that name resolves to /proc/self/fd, which was opened above. 78 However, on Solaris, it may resolve to /proc/self/fd/fd, which 79 cannot exist, since all names in /proc/self/fd are numeric. */ 80 char dotdot_buf[PROC_SELF_FD_NAME_SIZE_BOUND (sizeof "../fd" - 1)]; 81 sprintf (dotdot_buf, PROC_SELF_FD_FORMAT, proc_self_fd, "../fd"); 82 proc_status = access (dotdot_buf, F_OK) ? -1 : 1; 83 close (proc_self_fd); 84 } 85 } 86 87 if (proc_status < 0) 88 return NULL; 89 else 90 { 91 size_t bufsize = PROC_SELF_FD_NAME_SIZE_BOUND (strlen (file)); 92 char *result = buf; 93 if (OPENAT_BUFFER_SIZE < bufsize) 94 { 95 result = malloc (bufsize); 96 if (! result) 97 return NULL; 98 } 99 sprintf (result, PROC_SELF_FD_FORMAT, fd, file); 100 return result; 101 } 102 } 103