[PATCH 05/25] virtiofsd: passthrough_ll: add fd_map to hide file descriptors

[Dr. David Alan Gilbert (git)]

From: Stefan Hajnoczi <address@hidden>

Do not expose file descriptor numbers to clients.  This prevents the
abuse of internal file descriptors (like stdin/stdout).

Signed-off-by: Stefan Hajnoczi <address@hidden>
---
 contrib/virtiofsd/passthrough_ll.c | 113 +++++++++++++++++++++++------
 1 file changed, 92 insertions(+), 21 deletions(-)

diff --git a/contrib/virtiofsd/passthrough_ll.c 
b/contrib/virtiofsd/passthrough_ll.c
index 9f82166079..a71fbff143 100644
--- a/contrib/virtiofsd/passthrough_ll.c
+++ b/contrib/virtiofsd/passthrough_ll.c
@@ -60,6 +60,7 @@ struct lo_map_elem {
        union {
                struct lo_inode *inode;
                struct lo_dirp *dirp;
+               int fd;
                ssize_t freelist;
        };
        bool in_use;
@@ -107,6 +108,7 @@ struct lo_data {
        struct lo_inode root; /* protected by lo->mutex */
        struct lo_map ino_map; /* protected by lo->mutex */
        struct lo_map dirp_map; /* protected by lo->mutex */
+       struct lo_map fd_map; /* protected by lo->mutex */
 };
 
 static const struct fuse_opt lo_opts[] = {
@@ -241,6 +243,19 @@ static void lo_map_remove(struct lo_map *map, size_t key)
        map->freelist = key;
 }
 
+/* Assumes lo->mutex is held */
+static ssize_t lo_add_fd_mapping(fuse_req_t req, int fd)
+{
+       struct lo_map_elem *elem;
+
+       elem = lo_map_alloc_elem(&lo_data(req)->fd_map);
+       if (!elem)
+               return -1;
+
+       elem->fd = fd;
+       return elem - lo_data(req)->fd_map.elems;
+}
+
 /* Assumes lo->mutex is held */
 static ssize_t lo_add_dirp_mapping(fuse_req_t req, struct lo_dirp *dirp)
 {
@@ -350,6 +365,21 @@ static int utimensat_empty_nofollow(struct lo_inode *inode,
        return utimensat(AT_FDCWD, procname, tv, 0);
 }
 
+static int lo_fi_fd(fuse_req_t req, struct fuse_file_info *fi)
+{
+       struct lo_data *lo = lo_data(req);
+       struct lo_map_elem *elem;
+
+       pthread_mutex_lock(&lo->mutex);
+       elem = lo_map_get(&lo->fd_map, fi->fh);
+       pthread_mutex_unlock(&lo->mutex);
+
+       if (!elem)
+               return -1;
+
+       return elem->fd;
+}
+
 static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
                       int valid, struct fuse_file_info *fi)
 {
@@ -358,6 +388,7 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, 
struct stat *attr,
        struct lo_inode *inode;
        int ifd;
        int res;
+       int fd;
 
        inode = lo_inode(req, ino);
        if (!inode) {
@@ -367,9 +398,13 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, 
struct stat *attr,
 
        ifd = inode->fd;
 
+       /* If fi->fh is invalid we'll report EBADF later */
+       if (fi)
+               fd = lo_fi_fd(req, fi);
+
        if (valid & FUSE_SET_ATTR_MODE) {
                if (fi) {
-                       res = fchmod(fi->fh, attr->st_mode);
+                       res = fchmod(fd, attr->st_mode);
                } else {
                        sprintf(procname, "/proc/self/fd/%i", ifd);
                        res = chmod(procname, attr->st_mode);
@@ -390,7 +425,7 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, 
struct stat *attr,
        }
        if (valid & FUSE_SET_ATTR_SIZE) {
                if (fi) {
-                       res = ftruncate(fi->fh, attr->st_size);
+                       res = ftruncate(fd, attr->st_size);
                } else {
                        sprintf(procname, "/proc/self/fd/%i", ifd);
                        res = truncate(procname, attr->st_size);
@@ -417,7 +452,7 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, 
struct stat *attr,
                        tv[1] = attr->st_mtim;
 
                if (fi)
-                       res = futimens(fi->fh, tv);
+                       res = futimens(fd, tv);
                else
                        res = utimensat_empty_nofollow(inode, tv);
                if (res == -1)
@@ -1041,7 +1076,18 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, 
const char *name,
        lo_restore_cred(&old);
 
        if (!err) {
-               fi->fh = fd;
+               ssize_t fh;
+
+               pthread_mutex_lock(&lo->mutex);
+               fh = lo_add_fd_mapping(req, fd);
+               pthread_mutex_unlock(&lo->mutex);
+               if (fh == -1) {
+                       close(fd);
+                       fuse_reply_err(req, ENOMEM);
+                       return;
+               }
+
+               fi->fh = fh;
                err = lo_do_lookup(req, parent, name, &e);
        }
        if (lo->cache == CACHE_NEVER)
@@ -1082,6 +1128,7 @@ static void lo_fsyncdir(fuse_req_t req, fuse_ino_t ino, 
int datasync,
 static void lo_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi)
 {
        int fd;
+       ssize_t fh;
        char buf[64];
        struct lo_data *lo = lo_data(req);
 
@@ -1110,7 +1157,16 @@ static void lo_open(fuse_req_t req, fuse_ino_t ino, 
struct fuse_file_info *fi)
        if (fd == -1)
                return (void) fuse_reply_err(req, errno);
 
-       fi->fh = fd;
+       pthread_mutex_lock(&lo->mutex);
+       fh = lo_add_fd_mapping(req, fd);
+       pthread_mutex_unlock(&lo->mutex);
+       if (fh == -1) {
+               close(fd);
+               fuse_reply_err(req, ENOMEM);
+               return;
+       }
+
+       fi->fh = fh;
        if (lo->cache == CACHE_NEVER)
                fi->direct_io = 1;
        else if (lo->cache == CACHE_ALWAYS)
@@ -1120,9 +1176,18 @@ static void lo_open(fuse_req_t req, fuse_ino_t ino, 
struct fuse_file_info *fi)
 
 static void lo_release(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info 
*fi)
 {
+       struct lo_data *lo = lo_data(req);
+       int fd;
+
        (void) ino;
 
-       close(fi->fh);
+       fd = lo_fi_fd(req, fi);
+
+       pthread_mutex_lock(&lo->mutex);
+       lo_map_remove(&lo->fd_map, fi->fh);
+       pthread_mutex_unlock(&lo->mutex);
+
+       close(fd);
        fuse_reply_err(req, 0);
 }
 
@@ -1130,7 +1195,7 @@ static void lo_flush(fuse_req_t req, fuse_ino_t ino, 
struct fuse_file_info *fi)
 {
        int res;
        (void) ino;
-       res = close(dup(fi->fh));
+       res = close(dup(lo_fi_fd(req, fi)));
        fuse_reply_err(req, res == -1 ? errno : 0);
 }
 
@@ -1155,7 +1220,7 @@ static void lo_fsync(fuse_req_t req, fuse_ino_t ino, int 
datasync,
                if (fd == -1)
                        return (void) fuse_reply_err(req, errno);
        } else
-               fd = fi->fh;
+               fd = lo_fi_fd(req, fi);
 
        if (datasync)
                res = fdatasync(fd);
@@ -1176,7 +1241,7 @@ static void lo_read(fuse_req_t req, fuse_ino_t ino, 
size_t size,
                        "off=%lu)\n", ino, size, (unsigned long) offset);
 
        buf.buf[0].flags = FUSE_BUF_IS_FD | FUSE_BUF_FD_SEEK;
-       buf.buf[0].fd = fi->fh;
+       buf.buf[0].fd = lo_fi_fd(req, fi);
        buf.buf[0].pos = offset;
 
        fuse_reply_data(req, &buf, FUSE_BUF_SPLICE_MOVE);
@@ -1191,7 +1256,7 @@ static void lo_write_buf(fuse_req_t req, fuse_ino_t ino,
        struct fuse_bufvec out_buf = FUSE_BUFVEC_INIT(fuse_buf_size(in_buf));
 
        out_buf.buf[0].flags = FUSE_BUF_IS_FD | FUSE_BUF_FD_SEEK;
-       out_buf.buf[0].fd = fi->fh;
+       out_buf.buf[0].fd = lo_fi_fd(req, fi);
        out_buf.buf[0].pos = off;
 
        if (lo_debug(req))
@@ -1234,7 +1299,8 @@ static void lo_fallocate(fuse_req_t req, fuse_ino_t ino, 
int mode,
                return;
        }
 
-       err = posix_fallocate(fi->fh, offset, length);
+       err = posix_fallocate(lo_fi_fd(req, fi), offset,
+                             length);
 #endif
 
        fuse_reply_err(req, err);
@@ -1246,7 +1312,7 @@ static void lo_flock(fuse_req_t req, fuse_ino_t ino, 
struct fuse_file_info *fi,
        int res;
        (void) ino;
 
-       res = flock(fi->fh, op);
+       res = flock(lo_fi_fd(req, fi), op);
 
        fuse_reply_err(req, res == -1 ? errno : 0);
 }
@@ -1458,17 +1524,20 @@ static void lo_copy_file_range(fuse_req_t req, 
fuse_ino_t ino_in, off_t off_in,
                               struct fuse_file_info *fi_out, size_t len,
                               int flags)
 {
+       int in_fd, out_fd;
        ssize_t res;
 
-       if (lo_debug(req))
-               fuse_log(FUSE_LOG_DEBUG, "lo_copy_file_range(ino=%" PRIu64 
"/fd=%lu, "
-                               "off=%lu, ino=%" PRIu64 "/fd=%lu, "
-                               "off=%lu, size=%zd, flags=0x%x)\n",
-                       ino_in, fi_in->fh, off_in, ino_out, fi_out->fh, off_out,
-                       len, flags);
-
-       res = copy_file_range(fi_in->fh, &off_in, fi_out->fh, &off_out, len,
-                             flags);
+       in_fd = lo_fi_fd(req, fi_in);
+       out_fd = lo_fi_fd(req, fi_out);
+
+       fuse_log(FUSE_LOG_DEBUG,
+                "lo_copy_file_range(ino=%" PRIu64 "/fd=%d, "
+                "off=%lu, ino=%" PRIu64 "/fd=%d, "
+                "off=%lu, size=%zd, flags=0x%x)\n",
+                ino_in, in_fd, off_in, ino_out, out_fd, off_out, len,
+                flags);
+
+       res = copy_file_range(in_fd, &off_in, out_fd, &off_out, len, flags);
        if (res < 0)
                fuse_reply_err(req, -errno);
        else
@@ -1552,6 +1621,7 @@ int main(int argc, char *argv[])
        root_elem->inode = &lo.root;
 
        lo_map_init(&lo.dirp_map);
+       lo_map_init(&lo.fd_map);
 
        if (fuse_parse_cmdline(&args, &opts) != 0)
                return 1;
@@ -1646,6 +1716,7 @@ err_out2:
 err_out1:
        fuse_opt_free_args(&args);
 
+       lo_map_destroy(&lo.fd_map);
        lo_map_destroy(&lo.dirp_map);
        lo_map_destroy(&lo.ino_map);
 
-- 
2.23.0