Changes in uspace/srv/fs/fat/fat_ops.c [1313ee9:3c11713] in mainline

File:

• uspace/srv/fs/fat/fat_ops.c (modified) (3 diffs)

uspace/srv/fs/fat/fat_ops.c

@@ -290 +290 @@
 
         *nodepp = nodep;
+        return EOK;
+}
+
+/** Perform basic sanity checks on the file system.
+ *
+ * Verify if values of boot sector fields are sane. Also verify media
+ * descriptor. This is used to rule out cases when a device obviously
+ * does not contain a fat file system.
+ */
+static int fat_sanity_check(fat_bs_t *bs, dev_handle_t dev_handle)
+{
+        fat_cluster_t e0, e1;
+        unsigned fat_no;
+        int rc;
+
+        /* Check number of FATs. */
+        if (bs->fatcnt == 0)
+                return ENOTSUP;
+
+        /* Check total number of sectors. */
+
+        if (bs->totsec16 == 0 && bs->totsec32 == 0)
+                return ENOTSUP;
+
+        if (bs->totsec16 != 0 && bs->totsec32 != 0 &&
+            bs->totsec16 != bs->totsec32) 
+                return ENOTSUP;
+
+        /* Check media descriptor. Must be between 0xf0 and 0xff. */
+        if ((bs->mdesc & 0xf0) != 0xf0)
+                return ENOTSUP;
+
+        /* Check number of sectors per FAT. */
+        if (bs->sec_per_fat == 0)
+                return ENOTSUP;
+
+        /*
+         * Check that the root directory entries take up whole blocks.
+         * This check is rather strict, but it allows us to treat the root
+         * directory and non-root directories uniformly in some places.
+         * It can be removed provided that functions such as fat_read() are
+         * sanitized to support file systems with this property.
+         */
+        if ((uint16_t_le2host(bs->root_ent_max) * sizeof(fat_dentry_t)) %
+            uint16_t_le2host(bs->bps) != 0)
+                return ENOTSUP;
+
+        /* Check signature of each FAT. */
+
+        for (fat_no = 0; fat_no < bs->fatcnt; fat_no++) {
+                rc = fat_get_cluster(bs, dev_handle, fat_no, 0, &e0);
+                if (rc != EOK)
+                        return EIO;
+
+                rc = fat_get_cluster(bs, dev_handle, fat_no, 1, &e1);
+                if (rc != EOK)
+                        return EIO;
+
+                /* Check that first byte of FAT contains the media descriptor. */
+                if ((e0 & 0xff) != bs->mdesc)
+                        return ENOTSUP;
+
+                /*
+                 * Check that remaining bits of the first two entries are
+                 * set to one.
+                 */
+                if ((e0 >> 8) != 0xff || e1 != 0xffff)
+                        return ENOTSUP;
+        }
+
         return EOK;
 }
@@ -981 +1051 @@
         }
 
+        /* Do some simple sanity checks on the file system. */
+        rc = fat_sanity_check(bs, dev_handle);
+        if (rc != EOK) {
+                block_fini(dev_handle);
+                ipc_answer_0(rid, rc);
+                return;
+        }
+
         rc = fat_idx_init_by_dev_handle(dev_handle);
         if (rc != EOK) {
@@ -1037 +1115 @@
 {
         libfs_mount(&fat_libfs_ops, fat_reg.fs_handle, rid, request);
+}
+
+void fat_unmounted(ipc_callid_t rid, ipc_call_t *request)
+{
+        ipc_answer_0(rid, ENOTSUP);
+}
+
+void fat_unmount(ipc_callid_t rid, ipc_call_t *request)
+{
+        libfs_unmount(&fat_libfs_ops, rid, request);
 }