From 03effbc021064bb77d231ae5ca02d1a579c71ee1 Mon Sep 17 00:00:00 2001 From: "Dr. David Alan Gilbert" Date: Mon, 27 Jan 2020 19:01:17 +0100 Subject: [PATCH 046/116] virtiofsd: passthrough_ll: add fallback for racy ops MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit RH-Author: Dr. David Alan Gilbert Message-id: <20200127190227.40942-43-dgilbert@redhat.com> Patchwork-id: 93496 O-Subject: [RHEL-AV-8.2 qemu-kvm PATCH 042/112] virtiofsd: passthrough_ll: add fallback for racy ops Bugzilla: 1694164 RH-Acked-by: Philippe Mathieu-Daudé RH-Acked-by: Stefan Hajnoczi RH-Acked-by: Sergio Lopez Pascual From: Miklos Szeredi 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 Reviewed-by: Masayoshi Mizuma Signed-off-by: Dr. David Alan Gilbert (cherry picked from commit 5fe319a7b19c9c328e6e061bffcf1ff6cc8b89ce) Signed-off-by: Miroslav Rezanina --- tools/virtiofsd/helper.c | 5 +- tools/virtiofsd/passthrough_ll.c | 157 +++++++++++++++++++++++++++++++++++---- 2 files changed, 145 insertions(+), 17 deletions(-) diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c index b8ec5ac..5531425 100644 --- a/tools/virtiofsd/helper.c +++ b/tools/virtiofsd/helper.c @@ -142,7 +142,10 @@ void fuse_cmdline_help(void) " --daemonize run in background\n" " -o max_idle_threads the maximum number of idle worker " "threads\n" - " allowed (default: 10)\n"); + " allowed (default: 10)\n" + " -o norace disable racy fallback\n" + " default: false\n" + ); } static int fuse_helper_opt_proc(void *data, const char *arg, int key, diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c index 9815bfa..ac380ef 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, "%s: readlink failed: %m\n", __func__); + goto fail_noretry; + } + + if (res >= PATH_MAX) { + 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, + "%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, + "%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, + "%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, + "%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, + "%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, procname, tv, 0); + return utimensat(AT_FDCWD, path, 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; @@ -709,24 +820,38 @@ 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, @@ -748,7 +873,7 @@ 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; } -- 1.8.3.1