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Diffstat (limited to 'lib/openat.c')
| -rw-r--r-- | lib/openat.c | 312 |
1 files changed, 312 insertions, 0 deletions
diff --git a/lib/openat.c b/lib/openat.c new file mode 100644 index 0000000..baf6566 --- /dev/null +++ b/lib/openat.c @@ -0,0 +1,312 @@ +/* provide a replacement openat function + Copyright (C) 2004-2020 Free Software Foundation, Inc. + + This program is free software: you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program 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 General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see <https://www.gnu.org/licenses/>. */ + +/* written by Jim Meyering */ + +/* If the user's config.h happens to include <fcntl.h>, let it include only + the system's <fcntl.h> here, so that orig_openat doesn't recurse to + rpl_openat. */ +#define __need_system_fcntl_h +#include <config.h> + +/* Get the original definition of open. It might be defined as a macro. */ +#include <fcntl.h> +#include <sys/types.h> +#undef __need_system_fcntl_h + +#if HAVE_OPENAT +static int +orig_openat (int fd, char const *filename, int flags, mode_t mode) +{ + return openat (fd, filename, flags, mode); +} +#endif + +/* Write "fcntl.h" here, not <fcntl.h>, otherwise OSF/1 5.1 DTK cc eliminates + this include because of the preliminary #include <fcntl.h> above. */ +#include "fcntl.h" + +#include "openat.h" + +#include "cloexec.h" + +#include <stdarg.h> +#include <stdbool.h> +#include <stddef.h> +#include <stdlib.h> +#include <string.h> +#include <sys/stat.h> +#include <errno.h> + +#if HAVE_OPENAT + +/* Like openat, but support O_CLOEXEC and work around Solaris 9 bugs + with trailing slash. */ +int +rpl_openat (int dfd, char const *filename, int flags, ...) +{ + /* 0 = unknown, 1 = yes, -1 = no. */ +#if GNULIB_defined_O_CLOEXEC + int have_cloexec = -1; +#else + static int have_cloexec; +#endif + + mode_t mode; + int fd; + + mode = 0; + if (flags & O_CREAT) + { + va_list arg; + va_start (arg, flags); + + /* We have to use PROMOTED_MODE_T instead of mode_t, otherwise GCC 4 + creates crashing code when 'mode_t' is smaller than 'int'. */ + mode = va_arg (arg, PROMOTED_MODE_T); + + va_end (arg); + } + +# if OPEN_TRAILING_SLASH_BUG + /* Fail if one of O_CREAT, O_WRONLY, O_RDWR is specified and the filename + ends in a slash, as POSIX says such a filename must name a directory + <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>: + "A pathname that contains at least one non-<slash> character and that + ends with one or more trailing <slash> characters shall not be resolved + successfully unless the last pathname component before the trailing + <slash> characters names an existing directory" + If the named file already exists as a directory, then + - if O_CREAT is specified, open() must fail because of the semantics + of O_CREAT, + - if O_WRONLY or O_RDWR is specified, open() must fail because POSIX + <https://pubs.opengroup.org/onlinepubs/9699919799/functions/openat.html> + says that it fails with errno = EISDIR in this case. + If the named file does not exist or does not name a directory, then + - if O_CREAT is specified, open() must fail since open() cannot create + directories, + - if O_WRONLY or O_RDWR is specified, open() must fail because the + file does not contain a '.' directory. */ + if ((flags & O_CREAT) + || (flags & O_ACCMODE) == O_RDWR + || (flags & O_ACCMODE) == O_WRONLY) + { + size_t len = strlen (filename); + if (len > 0 && filename[len - 1] == '/') + { + errno = EISDIR; + return -1; + } + } +# endif + + fd = orig_openat (dfd, filename, + flags & ~(have_cloexec < 0 ? O_CLOEXEC : 0), mode); + + if (flags & O_CLOEXEC) + { + if (! have_cloexec) + { + if (0 <= fd) + have_cloexec = 1; + else if (errno == EINVAL) + { + fd = orig_openat (dfd, filename, flags & ~O_CLOEXEC, mode); + have_cloexec = -1; + } + } + if (have_cloexec < 0 && 0 <= fd) + set_cloexec_flag (fd, true); + } + + +# if OPEN_TRAILING_SLASH_BUG + /* If the filename ends in a slash and fd does not refer to a directory, + then fail. + Rationale: POSIX says such a filename must name a directory + <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>: + "A pathname that contains at least one non-<slash> character and that + ends with one or more trailing <slash> characters shall not be resolved + successfully unless the last pathname component before the trailing + <slash> characters names an existing directory" + If the named file without the slash is not a directory, open() must fail + with ENOTDIR. */ + if (fd >= 0) + { + /* We know len is positive, since open did not fail with ENOENT. */ + size_t len = strlen (filename); + if (filename[len - 1] == '/') + { + struct stat statbuf; + + if (fstat (fd, &statbuf) >= 0 && !S_ISDIR (statbuf.st_mode)) + { + close (fd); + errno = ENOTDIR; + return -1; + } + } + } +# endif + + return fd; +} + +#else /* !HAVE_OPENAT */ + +# include "filename.h" /* solely for definition of IS_ABSOLUTE_FILE_NAME */ +# include "openat-priv.h" +# include "save-cwd.h" + +/* Replacement for Solaris' openat function. + <https://www.google.com/search?q=openat+site:docs.oracle.com> + First, try to simulate it via open ("/proc/self/fd/FD/FILE"). + Failing that, simulate it by doing save_cwd/fchdir/open/restore_cwd. + If either the save_cwd or the restore_cwd fails (relatively unlikely), + then give a diagnostic and exit nonzero. + Otherwise, upon failure, set errno and return -1, as openat does. + Upon successful completion, return a file descriptor. */ +int +openat (int fd, char const *file, int flags, ...) +{ + mode_t mode = 0; + + if (flags & O_CREAT) + { + va_list arg; + va_start (arg, flags); + + /* We have to use PROMOTED_MODE_T instead of mode_t, otherwise GCC 4 + creates crashing code when 'mode_t' is smaller than 'int'. */ + mode = va_arg (arg, PROMOTED_MODE_T); + + va_end (arg); + } + + return openat_permissive (fd, file, flags, mode, NULL); +} + +/* Like openat (FD, FILE, FLAGS, MODE), but if CWD_ERRNO is + nonnull, set *CWD_ERRNO to an errno value if unable to save + or restore the initial working directory. This is needed only + the first time remove.c's remove_dir opens a command-line + directory argument. + + If a previous attempt to restore the current working directory + failed, then we must not even try to access a '.'-relative name. + It is the caller's responsibility not to call this function + in that case. */ + +int +openat_permissive (int fd, char const *file, int flags, mode_t mode, + int *cwd_errno) +{ + struct saved_cwd saved_cwd; + int saved_errno; + int err; + bool save_ok; + + if (fd == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file)) + return open (file, flags, mode); + + { + char buf[OPENAT_BUFFER_SIZE]; + char *proc_file = openat_proc_name (buf, fd, file); + if (proc_file) + { + int open_result = open (proc_file, flags, mode); + int open_errno = errno; + if (proc_file != buf) + free (proc_file); + /* If the syscall succeeds, or if it fails with an unexpected + errno value, then return right away. Otherwise, fall through + and resort to using save_cwd/restore_cwd. */ + if (0 <= open_result || ! EXPECTED_ERRNO (open_errno)) + { + errno = open_errno; + return open_result; + } + } + } + + save_ok = (save_cwd (&saved_cwd) == 0); + if (! save_ok) + { + if (! cwd_errno) + openat_save_fail (errno); + *cwd_errno = errno; + } + if (0 <= fd && fd == saved_cwd.desc) + { + /* If saving the working directory collides with the user's + requested fd, then the user's fd must have been closed to + begin with. */ + free_cwd (&saved_cwd); + errno = EBADF; + return -1; + } + + err = fchdir (fd); + saved_errno = errno; + + if (! err) + { + err = open (file, flags, mode); + saved_errno = errno; + if (save_ok && restore_cwd (&saved_cwd) != 0) + { + if (! cwd_errno) + { + /* Don't write a message to just-created fd 2. */ + saved_errno = errno; + if (err == STDERR_FILENO) + close (err); + openat_restore_fail (saved_errno); + } + *cwd_errno = errno; + } + } + + free_cwd (&saved_cwd); + errno = saved_errno; + return err; +} + +/* Return true if our openat implementation must resort to + using save_cwd and restore_cwd. */ +bool +openat_needs_fchdir (void) +{ + bool needs_fchdir = true; + int fd = open ("/", O_SEARCH | O_CLOEXEC); + + if (0 <= fd) + { + char buf[OPENAT_BUFFER_SIZE]; + char *proc_file = openat_proc_name (buf, fd, "."); + if (proc_file) + { + needs_fchdir = false; + if (proc_file != buf) + free (proc_file); + } + close (fd); + } + + return needs_fchdir; +} + +#endif /* !HAVE_OPENAT */ |