* Masayoshi Mizuma (msys.miz...@gmail.com) wrote: > On Thu, Dec 12, 2019 at 04:37:57PM +0000, Dr. David Alan Gilbert (git) wrote: > > From: Miklos Szeredi <mszer...@redhat.com> > > > > We have two operations that cannot be done race-free on a symlink in > > certain cases: utimes and link. > > > > Add racy fallback for these if the race-free method doesn't work. We do > > our best to avoid races even in this case: > > > > - get absolute path by reading /proc/self/fd/NN symlink > > > > - lookup parent directory: after this we are safe against renames in > > ancestors > > > > - lookup name in parent directory, and verify that we got to the original > > inode, if not retry the whole thing > > > > Both utimes(2) and link(2) hold i_lock on the inode across the operation, > > so a racing rename/delete by this fuse instance is not possible, only from > > other entities changing the filesystem. > > > > If the "norace" option is given, then disable the racy fallbacks. > > > > Signed-off-by: Miklos Szeredi <mszer...@redhat.com> > > --- > > tools/virtiofsd/passthrough_ll.c | 159 +++++++++++++++++++++++++++---- > > 1 file changed, 142 insertions(+), 17 deletions(-) > > > > diff --git a/tools/virtiofsd/passthrough_ll.c > > b/tools/virtiofsd/passthrough_ll.c > > index 93e74cce21..1faae2753f 100644 > > --- a/tools/virtiofsd/passthrough_ll.c > > +++ b/tools/virtiofsd/passthrough_ll.c > > @@ -98,6 +98,7 @@ enum { > > struct lo_data { > > pthread_mutex_t mutex; > > int debug; > > + int norace; > > int writeback; > > int flock; > > int xattr; > > @@ -124,10 +125,15 @@ static const struct fuse_opt lo_opts[] = { > > { "cache=never", offsetof(struct lo_data, cache), CACHE_NEVER }, > > { "cache=auto", offsetof(struct lo_data, cache), CACHE_NORMAL }, > > { "cache=always", offsetof(struct lo_data, cache), CACHE_ALWAYS }, > > - > > + { "norace", offsetof(struct lo_data, norace), 1 }, > > FUSE_OPT_END > > }; > > > > +static void unref_inode(struct lo_data *lo, struct lo_inode *inode, > > uint64_t n); > > + > > +static struct lo_inode *lo_find(struct lo_data *lo, struct stat *st); > > + > > + > > static struct lo_data *lo_data(fuse_req_t req) > > { > > return (struct lo_data *)fuse_req_userdata(req); > > @@ -347,23 +353,127 @@ static void lo_getattr(fuse_req_t req, fuse_ino_t > > ino, > > fuse_reply_attr(req, &buf, lo->timeout); > > } > > > -static int utimensat_empty_nofollow(struct lo_inode *inode, > > - const struct timespec *tv) > > +static int lo_parent_and_name(struct lo_data *lo, struct lo_inode *inode, > > + char path[PATH_MAX], struct lo_inode > > **parent) > > { > > - int res; > > char procname[64]; > > + char *last; > > + struct stat stat; > > + struct lo_inode *p; > > + int retries = 2; > > + int res; > > + > > +retry: > > + sprintf(procname, "/proc/self/fd/%i", inode->fd); > > + > > + res = readlink(procname, path, PATH_MAX); > > + if (res < 0) { > > > + fuse_log(FUSE_LOG_WARNING, "lo_parent_and_name: readlink failed: > > %m\n"); > > I think it's better to use __func__ macro in case the function name is > changed in the future.
Yes, agreed - I've changed them all > fuse_log(FUSE_LOG_WARNING, "%s: readlink failed: %m\n", __func__); > > > + goto fail_noretry; > > + } > > + > > + if (res >= PATH_MAX) { > > > + fuse_log(FUSE_LOG_WARNING, "lo_parent_and_name: readlink > > overflowed\n"); > > fuse_log(FUSE_LOG_WARNING, "%s: readlink overflowed\n", __func__); > > > + goto fail_noretry; > > + } > > + path[res] = '\0'; > > + > > + last = strrchr(path, '/'); > > + if (last == NULL) { > > + /* Shouldn't happen */ > > > + fuse_log( > > + FUSE_LOG_WARNING, > > + "lo_parent_and_name: INTERNAL ERROR: bad path read from > > proc\n"); > > fuse_log( > FUSE_LOG_WARNING, > "%s: INTERNAL ERROR: bad path read from proc\n", __func__); > > > + goto fail_noretry; > > + } > > + if (last == path) { > > + p = &lo->root; > > + pthread_mutex_lock(&lo->mutex); > > + p->refcount++; > > + pthread_mutex_unlock(&lo->mutex); > > + } else { > > + *last = '\0'; > > + res = fstatat(AT_FDCWD, last == path ? "/" : path, &stat, 0); > > + if (res == -1) { > > + if (!retries) { > > > + fuse_log(FUSE_LOG_WARNING, > > + "lo_parent_and_name: failed to stat parent: > > %m\n"); > > fuse_log(FUSE_LOG_WARNING, > "%s: failed to stat parent: %m\n", __func__); > > > + } > > + goto fail; > > + } > > + p = lo_find(lo, &stat); > > + if (p == NULL) { > > + if (!retries) { > > > + fuse_log(FUSE_LOG_WARNING, > > + "lo_parent_and_name: failed to find parent\n"); > > fuse_log(FUSE_LOG_WARNING, > "%s: failed to find parent\n", __func__); > > > + } > > + goto fail; > > + } > > + } > > + last++; > > + res = fstatat(p->fd, last, &stat, AT_SYMLINK_NOFOLLOW); > > + if (res == -1) { > > + if (!retries) { > > > + fuse_log(FUSE_LOG_WARNING, > > + "lo_parent_and_name: failed to stat last\n"); > > fuse_log(FUSE_LOG_WARNING, > "%s: failed to stat last\n", __func__); > > > + } > > + goto fail_unref; > > + } > > + if (stat.st_dev != inode->dev || stat.st_ino != inode->ino) { > > + if (!retries) { > > > + fuse_log(FUSE_LOG_WARNING, > > + "lo_parent_and_name: failed to match last\n"); > > fuse_log(FUSE_LOG_WARNING, > "%s: failed to match last\n", __func__); > > > + } > > + goto fail_unref; > > + } > > + *parent = p; > > + memmove(path, last, strlen(last) + 1); > > + > > + return 0; > > + > > +fail_unref: > > + unref_inode(lo, p, 1); > > +fail: > > + if (retries) { > > + retries--; > > + goto retry; > > + } > > +fail_noretry: > > + errno = EIO; > > + return -1; > > +} > > + > > +static int utimensat_empty(struct lo_data *lo, struct lo_inode *inode, > > + const struct timespec *tv) > > +{ > > + int res; > > + struct lo_inode *parent; > > + char path[PATH_MAX]; > > > > if (inode->is_symlink) { > > - res = utimensat(inode->fd, "", tv, AT_EMPTY_PATH | > > AT_SYMLINK_NOFOLLOW); > > + res = utimensat(inode->fd, "", tv, AT_EMPTY_PATH); > > if (res == -1 && errno == EINVAL) { > > /* Sorry, no race free way to set times on symlink. */ > > - errno = EPERM; > > + if (lo->norace) { > > + errno = EPERM; > > + } else { > > + goto fallback; > > + } > > } > > return res; > > } > > - sprintf(procname, "/proc/self/fd/%i", inode->fd); > > + sprintf(path, "/proc/self/fd/%i", inode->fd); > > + > > + return utimensat(AT_FDCWD, path, tv, 0); > > > > - return utimensat(AT_FDCWD, procname, tv, 0); > > +fallback: > > + res = lo_parent_and_name(lo, inode, path, &parent); > > + if (res != -1) { > > + res = utimensat(parent->fd, path, tv, AT_SYMLINK_NOFOLLOW); > > + unref_inode(lo, parent, 1); > > + } > > + > > + return res; > > } > > > > static int lo_fi_fd(fuse_req_t req, struct fuse_file_info *fi) > > @@ -387,6 +497,7 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, > > struct stat *attr, > > { > > int saverr; > > char procname[64]; > > + struct lo_data *lo = lo_data(req); > > struct lo_inode *inode; > > int ifd; > > int res; > > @@ -459,7 +570,7 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, > > struct stat *attr, > > if (fi) { > > res = futimens(fd, tv); > > } else { > > - res = utimensat_empty_nofollow(inode, tv); > > + res = utimensat_empty(lo, inode, tv); > > } > > if (res == -1) { > > goto out_err; > > @@ -692,24 +803,38 @@ static void lo_symlink(fuse_req_t req, const char > > *link, fuse_ino_t parent, > > lo_mknod_symlink(req, parent, name, S_IFLNK, 0, link); > > } > > > > -static int linkat_empty_nofollow(struct lo_inode *inode, int dfd, > > - const char *name) > > +static int linkat_empty_nofollow(struct lo_data *lo, struct lo_inode > > *inode, > > + int dfd, const char *name) > > { > > int res; > > - char procname[64]; > > + struct lo_inode *parent; > > + char path[PATH_MAX]; > > > > if (inode->is_symlink) { > > res = linkat(inode->fd, "", dfd, name, AT_EMPTY_PATH); > > if (res == -1 && (errno == ENOENT || errno == EINVAL)) { > > /* Sorry, no race free way to hard-link a symlink. */ > > - errno = EPERM; > > + if (lo->norace) { > > + errno = EPERM; > > + } else { > > + goto fallback; > > + } > > } > > return res; > > } > > > > - sprintf(procname, "/proc/self/fd/%i", inode->fd); > > + sprintf(path, "/proc/self/fd/%i", inode->fd); > > + > > + return linkat(AT_FDCWD, path, dfd, name, AT_SYMLINK_FOLLOW); > > + > > +fallback: > > + res = lo_parent_and_name(lo, inode, path, &parent); > > + if (res != -1) { > > + res = linkat(parent->fd, path, dfd, name, 0); > > + unref_inode(lo, parent, 1); > > + } > > > > - return linkat(AT_FDCWD, procname, dfd, name, AT_SYMLINK_FOLLOW); > > + return res; > > } > > > > static void lo_link(fuse_req_t req, fuse_ino_t ino, fuse_ino_t parent, > > @@ -731,7 +856,7 @@ static void lo_link(fuse_req_t req, fuse_ino_t ino, > > fuse_ino_t parent, > > e.attr_timeout = lo->timeout; > > e.entry_timeout = lo->timeout; > > > > - res = linkat_empty_nofollow(inode, lo_fd(req, parent), name); > > + res = linkat_empty_nofollow(lo, inode, lo_fd(req, parent), name); > > if (res == -1) { > > goto out_err; > > } > > @@ -1544,7 +1669,7 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t > > ino, const char *name, > > } > > > > if (inode->is_symlink) { > > - /* Sorry, no race free way to setxattr on symlink. */ > > + /* Sorry, no race free way to removexattr on symlink. */ I've undone that change; since it looks bogus. > > saverr = EPERM; > > goto out; > > } > > Reviewed-by: Masayoshi Mizuma <m.miz...@jp.fujitsu.com> Thanks. -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK