From: Stefan Hajnoczi <address@hidden>
Introduce lo_dirp_put() so that FUSE_RELEASEDIR does not cause
use-after-free races with other threads that are accessing lo_dirp.
Also make lo_releasedir() atomic to prevent FUSE_RELEASEDIR racing with
itself. This prevents double-frees.
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
tools/virtiofsd/passthrough_ll.c | 41 +++++++++++++++++++++++++++-----
1 file changed, 35 insertions(+), 6 deletions(-)
diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index eadd568435..7663e574d8 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -1317,11 +1317,28 @@ static void lo_readlink(fuse_req_t req, fuse_ino_t ino)
}
struct lo_dirp {
+ gint refcount;
DIR *dp;
struct dirent *entry;
off_t offset;
};
+static void lo_dirp_put(struct lo_dirp **dp)
+{
+ struct lo_dirp *d = *dp;
+
+ if (!d) {
+ return;
+ }
+ *dp = NULL;
+
+ if (g_atomic_int_dec_and_test(&d->refcount)) {
+ closedir(d->dp);
+ free(d);
+ }
+}
+
+/* Call lo_dirp_put() on the return value when no longer needed */
static struct lo_dirp *lo_dirp(fuse_req_t req, struct fuse_file_info *fi)
{
struct lo_data *lo = lo_data(req);
@@ -1329,6 +1346,9 @@ static struct lo_dirp *lo_dirp(fuse_req_t req, struct
fuse_file_info *fi)
pthread_mutex_lock(&lo->mutex);
elem = lo_map_get(&lo->dirp_map, fi->fh);
+ if (elem) {
+ g_atomic_int_inc(&elem->dirp->refcount);
+ }
pthread_mutex_unlock(&lo->mutex);
if (!elem) {
return NULL;
@@ -1364,6 +1384,7 @@ static void lo_opendir(fuse_req_t req, fuse_ino_t ino,
d->offset = 0;
d->entry = NULL;
+ g_atomic_int_set(&d->refcount, 1); /* paired with lo_releasedir() */
pthread_mutex_lock(&lo->mutex);
fh = lo_add_dirp_mapping(req, d);
pthread_mutex_unlock(&lo->mutex);
@@ -1397,7 +1418,7 @@ static void lo_do_readdir(fuse_req_t req, fuse_ino_t ino,
size_t size,
off_t offset, struct fuse_file_info *fi, int plus)
{
struct lo_data *lo = lo_data(req);
- struct lo_dirp *d;
+ struct lo_dirp *d = NULL;
struct lo_inode *dinode;
char *buf = NULL;
char *p;
@@ -1487,6 +1508,8 @@ static void lo_do_readdir(fuse_req_t req, fuse_ino_t ino,
size_t size,
err = 0;
error:
+ lo_dirp_put(&d);
+
/*
* If there's an error, we can only signal it if we haven't stored
* any entries yet - otherwise we'd end up with wrong lookup
@@ -1517,22 +1540,25 @@ static void lo_releasedir(fuse_req_t req, fuse_ino_t
ino,
struct fuse_file_info *fi)
{
struct lo_data *lo = lo_data(req);
+ struct lo_map_elem *elem;
struct lo_dirp *d;
(void)ino;
- d = lo_dirp(req, fi);
- if (!d) {
+ pthread_mutex_lock(&lo->mutex);
+ elem = lo_map_get(&lo->dirp_map, fi->fh);
+ if (!elem) {
+ pthread_mutex_unlock(&lo->mutex);
fuse_reply_err(req, EBADF);
return;
}
- pthread_mutex_lock(&lo->mutex);
+ d = elem->dirp;
lo_map_remove(&lo->dirp_map, fi->fh);
pthread_mutex_unlock(&lo->mutex);
- closedir(d->dp);
- free(d);
+ lo_dirp_put(&d); /* paired with lo_opendir() */
+
fuse_reply_err(req, 0);
}
@@ -1743,6 +1769,9 @@ static void lo_fsyncdir(fuse_req_t req, fuse_ino_t ino, int datasync,
} else {
res = fsync(fd);
}
+
+ lo_dirp_put(&d);
+
fuse_reply_err(req, res == -1 ? errno : 0);
}