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From: Ken Brown <kbrown@sourceware.org> To: cygwin-cvs@sourceware.org Subject: [newlib-cygwin] Cygwin: fstatat, fchownat: support the AT_EMPTY_PATH flag Date: Mon, 20 Jan 2020 14:49:00 -0000 [thread overview] Message-ID: <20200120144903.117312.qmail@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=352dbd304be48cd47de4f588031b98b8e0202f33 commit 352dbd304be48cd47de4f588031b98b8e0202f33 Author: Ken Brown <kbrown@cornell.edu> Date: Fri Dec 27 17:38:32 2019 -0500 Cygwin: fstatat, fchownat: support the AT_EMPTY_PATH flag Following Linux, allow the pathname argument to be an empty string if the AT_EMPTY_PATH flag is specified. In this case the dirfd argument can refer to any type of file, not just a directory, and the call operates on that file. In particular, dirfd can refer to a symlink that was opened with O_PATH | O_NOFOLLOW. Diff: --- winsup/cygwin/syscalls.cc | 47 +++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 41 insertions(+), 6 deletions(-) diff --git a/winsup/cygwin/syscalls.cc b/winsup/cygwin/syscalls.cc index 282d9e0..4956b6f 100644 --- a/winsup/cygwin/syscalls.cc +++ b/winsup/cygwin/syscalls.cc @@ -4785,14 +4785,36 @@ fchownat (int dirfd, const char *pathname, uid_t uid, gid_t gid, int flags) tmp_pathbuf tp; __try { - if (flags & ~AT_SYMLINK_NOFOLLOW) + if (flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) { set_errno (EINVAL); __leave; } char *path = tp.c_get (); - if (gen_full_path_at (path, dirfd, pathname)) - __leave; + int res = gen_full_path_at (path, dirfd, pathname); + if (res) + { + if (!(errno == ENOENT && (flags & AT_EMPTY_PATH))) + __leave; + /* pathname is an empty string. Operate on dirfd. */ + if (dirfd == AT_FDCWD) + { + cwdstuff::cwd_lock.acquire (); + strcpy (path, cygheap->cwd.get_posix ()); + cwdstuff::cwd_lock.release (); + } + else + { + cygheap_fdget cfd (dirfd); + if (cfd < 0) + __leave; + strcpy (path, cfd->get_name ()); + /* If dirfd refers to a symlink (which was necessarily + opened with O_PATH | O_NOFOLLOW), we must operate + directly on that symlink.. */ + flags = AT_SYMLINK_NOFOLLOW; + } + } return chown_worker (path, (flags & AT_SYMLINK_NOFOLLOW) ? PC_SYM_NOFOLLOW : PC_SYM_FOLLOW, uid, gid); } @@ -4808,14 +4830,27 @@ fstatat (int dirfd, const char *__restrict pathname, struct stat *__restrict st, tmp_pathbuf tp; __try { - if (flags & ~AT_SYMLINK_NOFOLLOW) + if (flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) { set_errno (EINVAL); __leave; } char *path = tp.c_get (); - if (gen_full_path_at (path, dirfd, pathname)) - __leave; + int res = gen_full_path_at (path, dirfd, pathname); + if (res) + { + if (!(errno == ENOENT && (flags & AT_EMPTY_PATH))) + __leave; + /* pathname is an empty string. Operate on dirfd. */ + if (dirfd == AT_FDCWD) + { + cwdstuff::cwd_lock.acquire (); + strcpy (path, cygheap->cwd.get_posix ()); + cwdstuff::cwd_lock.release (); + } + else + return fstat (dirfd, st); + } path_conv pc (path, ((flags & AT_SYMLINK_NOFOLLOW) ? PC_SYM_NOFOLLOW : PC_SYM_FOLLOW) | PC_POSIX | PC_KEEP_HANDLE, stat_suffixes);
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