@@ -668,7 +668,7 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
if (fs_ctx->export_flags & V9FS_SM_MAPPED ||
fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {
- err = mknodat(dirfd, name, fs_ctx->fmode | S_IFREG, 0);
+ err = qemu_mknodat(dirfd, name, fs_ctx->fmode | S_IFREG, 0);
if (err == -1) {
goto out;
}
@@ -683,7 +683,7 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
}
} else if (fs_ctx->export_flags & V9FS_SM_PASSTHROUGH ||
fs_ctx->export_flags & V9FS_SM_NONE) {
- err = mknodat(dirfd, name, credp->fc_mode, credp->fc_rdev);
+ err = qemu_mknodat(dirfd, name, credp->fc_mode, credp->fc_rdev);
if (err == -1) {
goto out;
}
@@ -696,6 +696,7 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
err_end:
unlinkat_preserve_errno(dirfd, name, 0);
+
out:
close_preserve_errno(dirfd);
return err;
@@ -158,3 +158,34 @@ done:
close_preserve_errno(fd);
return ret;
}
+
+#ifndef SYS___pthread_fchdir
+# define SYS___pthread_fchdir 349
+#endif
+
+// This is an undocumented OS X syscall. It would be best to avoid it,
+// but there doesn't seem to be another safe way to implement mknodat.
+// Dear Apple, please implement mknodat before you remove this syscall.
+static int fchdir_thread_local(int fd)
+{
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
+ return syscall(SYS___pthread_fchdir, fd);
+#pragma clang diagnostic pop
+}
+
+int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev)
+{
+ int preserved_errno, err;
+ if (fchdir_thread_local(dirfd) < 0) {
+ return -1;
+ }
+ err = mknod(filename, mode, dev);
+ preserved_errno = errno;
+ /* Stop using the thread-local cwd */
+ fchdir_thread_local(-1);
+ if (err < 0) {
+ errno = preserved_errno;
+ }
+ return err;
+}
@@ -63,3 +63,8 @@ int utimensat_nofollow(int dirfd, const char *filename,
{
return utimensat(dirfd, filename, times, AT_SYMLINK_NOFOLLOW);
}
+
+int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev)
+{
+ return mknodat(dirfd, filename, mode, dev);
+}
@@ -90,4 +90,6 @@ ssize_t fremovexattrat_nofollow(int dirfd, const char *filename,
int utimensat_nofollow(int dirfd, const char *filename,
const struct timespec times[2]);
+int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev);
+
#endif
Darwin does not support mknodat. However, to avoid race conditions with later setting the permissions, we must avoid using mknod on the full path instead. We could try to fchdir, but that would cause problems if multiple threads try to call mknodat at the same time. However, luckily there is a solution: Darwin as an (unexposed in the C library) system call that sets the cwd for the current thread only. This should suffice to use mknod safely. Signed-off-by: Keno Fischer <keno@juliacomputing.com> --- Changes since v2: - Silence clang warning for deprecated uses of `syscall`. It is unforunate that we have to use this depreacted interface, but there does not seem to be a better option. hw/9pfs/9p-local.c | 5 +++-- hw/9pfs/9p-util-darwin.c | 31 +++++++++++++++++++++++++++++++ hw/9pfs/9p-util-linux.c | 5 +++++ hw/9pfs/9p-util.h | 2 ++ 4 files changed, 41 insertions(+), 2 deletions(-)