1/* Create /proc/self/fd-related names for subfiles of open directories. 2 3 Copyright (C) 2006, 2009-2010 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 <string.h> 30#include <unistd.h> 31 32#include "dirname.h" 33#include "intprops.h" 34#include "same-inode.h" 35#include "xalloc.h" 36 37/* The results of open() in this file are not used with fchdir, 38 and we do not leak fds to any single-threaded code that could use stdio, 39 therefore save some unnecessary work in fchdir.c. 40 FIXME - if the kernel ever adds support for multi-thread safety for 41 avoiding standard fds, then we should use open_safer. */ 42#undef open 43#undef close 44 45#define PROC_SELF_FD_FORMAT "/proc/self/fd/%d/%s" 46 47#define PROC_SELF_FD_NAME_SIZE_BOUND(len) \ 48 (sizeof PROC_SELF_FD_FORMAT - sizeof "%d%s" \ 49 + INT_STRLEN_BOUND (int) + (len) + 1) 50 51 52/* Set BUF to the expansion of PROC_SELF_FD_FORMAT, using FD and FILE 53 respectively for %d and %s. If successful, return BUF if the 54 result fits in BUF, dynamically allocated memory otherwise. But 55 return NULL if /proc is not reliable. */ 56char * 57openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file) 58{ 59 static int proc_status = 0; 60 61 /* Make sure the caller gets ENOENT when appropriate. */ 62 if (!*file) 63 { 64 buf[0] = '\0'; 65 return buf; 66 } 67 68 if (! proc_status) 69 { 70 /* Set PROC_STATUS to a positive value if /proc/self/fd is 71 reliable, and a negative value otherwise. Solaris 10 72 /proc/self/fd mishandles "..", and any file name might expand 73 to ".." after symbolic link expansion, so avoid /proc/self/fd 74 if it mishandles "..". Solaris 10 has openat, but this 75 problem is exhibited on code that built on Solaris 8 and 76 running on Solaris 10. */ 77 78 int proc_self_fd = open ("/proc/self/fd", O_RDONLY); 79 if (proc_self_fd < 0) 80 proc_status = -1; 81 else 82 { 83 struct stat proc_self_fd_dotdot_st; 84 struct stat proc_self_st; 85 char dotdot_buf[PROC_SELF_FD_NAME_SIZE_BOUND (sizeof ".." - 1)]; 86 sprintf (dotdot_buf, PROC_SELF_FD_FORMAT, proc_self_fd, ".."); 87 proc_status = 88 ((stat (dotdot_buf, &proc_self_fd_dotdot_st) == 0 89 && stat ("/proc/self", &proc_self_st) == 0 90 && SAME_INODE (proc_self_fd_dotdot_st, proc_self_st)) 91 ? 1 : -1); 92 close (proc_self_fd); 93 } 94 } 95 96 if (proc_status < 0) 97 return NULL; 98 else 99 { 100 size_t bufsize = PROC_SELF_FD_NAME_SIZE_BOUND (strlen (file)); 101 char *result = (bufsize < OPENAT_BUFFER_SIZE ? buf : xmalloc (bufsize)); 102 sprintf (result, PROC_SELF_FD_FORMAT, fd, file); 103 return result; 104 } 105} 106