From: Miklos Szeredi <mszeredi@redhat.com>
Date: Mon, 27 Jan 2020 19:01:17 +0000
Subject: [PATCH] virtiofsd: passthrough_ll: add fallback for racy ops
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 <mszeredi@redhat.com>
Reviewed-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
(cherry picked from commit 5fe319a7b19c9c328e6e061bffcf1ff6cc8b89ce)
---
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 b8ec5ac8dc..5531425223 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 9815bfa5c5..ac380efcb1 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;
}