[PATCH 036/104] virtiofsd: passthrough_ll: add fd_map to hide file descriptors

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: Stefan Hajnoczi <stefanha@redhat.com>

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

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
dgilbert:
  Added lseek
---
 tools/virtiofsd/passthrough_ll.c | 114 +++++++++++++++++++++++++------
 1 file changed, 93 insertions(+), 21 deletions(-)

diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index face8910b0..93e74cce21 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/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[] = {
@@ -236,6 +238,20 @@ 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 +366,22 @@ 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 +390,7 @@ 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 +400,14 @@ 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);
@@ -389,7 +427,7 @@ 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);
@@ -419,7 +457,7 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
         }
 
         if (fi) {
-            res = futimens(fi->fh, tv);
+            res = futimens(fd, tv);
         } else {
             res = utimensat_empty_nofollow(inode, tv);
         }
@@ -1079,7 +1117,18 @@ 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) {
@@ -1123,6 +1172,7 @@ 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);
 
@@ -1158,7 +1208,16 @@ static void lo_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi)
         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) {
@@ -1170,9 +1229,18 @@ 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);
 }
 
@@ -1180,7 +1248,7 @@ 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);
 }
 
@@ -1207,7 +1275,7 @@ static void lo_fsync(fuse_req_t req, fuse_ino_t ino, int datasync,
             return (void)fuse_reply_err(req, errno);
         }
     } else {
-        fd = fi->fh;
+        fd = lo_fi_fd(req, fi);
     }
 
     if (datasync) {
@@ -1234,7 +1302,7 @@ static void lo_read(fuse_req_t req, fuse_ino_t ino, size_t size, off_t 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);
@@ -1249,7 +1317,7 @@ 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)) {
@@ -1297,7 +1365,7 @@ static void lo_fallocate(fuse_req_t req, fuse_ino_t ino, int mode, off_t offset,
         return;
     }
 
-    err = posix_fallocate(fi->fh, offset, length);
+    err = posix_fallocate(lo_fi_fd(req, fi), offset, length);
 #endif
 
     fuse_reply_err(req, err);
@@ -1309,7 +1377,7 @@ 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);
 }
@@ -1534,17 +1602,19 @@ static void lo_copy_file_range(fuse_req_t req, fuse_ino_t ino_in, off_t off_in,
                                off_t off_out, 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);
+    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(fi_in->fh, &off_in, fi_out->fh, &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 {
@@ -1559,7 +1629,7 @@ static void lo_lseek(fuse_req_t req, fuse_ino_t ino, off_t off, int whence,
     off_t res;
 
     (void)ino;
-    res = lseek(fi->fh, off, whence);
+    res = lseek(lo_fi_fd(req, fi), off, whence);
     if (res != -1) {
         fuse_reply_lseek(req, res);
     } else {
@@ -1644,6 +1714,7 @@ 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;
@@ -1741,6 +1812,7 @@ 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