fw_cfg: handle fw_cfg_read_blob() error

fw_cfg_read_blob() may fail, but does not return error. This may lead
to surprising behaviours, like populating zero file entries (in
register_file() or during read). Return an error if ACPI locking
failed. Also, the following DMA read/write extension will add more
error paths that should be handled appropriately.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 22 insertions, 10 deletions

diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
index 0cc71d028ae3..45bfc389b226 100644
--- a/drivers/firmware/qemu_fw_cfg.c
+++ b/drivers/firmware/qemu_fw_cfg.c
@@ -77,8 +77,8 @@ static void fw_cfg_sel_endianness(u16 key)
 }
 
 /* read chunk of given fw_cfg blob (caller responsible for sanity-check) */
-static void fw_cfg_read_blob(u16 key,
-                        void *buf, loff_t pos, size_t count)
+static ssize_t fw_cfg_read_blob(u16 key,
+                                void *buf, loff_t pos, size_t count)
 {
         u32 glk = -1U;
         acpi_status status;
@@ -91,7 +91,7 @@ static void fw_cfg_read_blob(u16 key,
                 /* Should never get here */
                 WARN(1, "fw_cfg_read_blob: Failed to lock ACPI!\n");
                 memset(buf, 0, count);
-                return;
+                return -EINVAL;
         }
 
         mutex_lock(&fw_cfg_dev_lock);
@@ -102,6 +102,7 @@ static void fw_cfg_read_blob(u16 key,
         mutex_unlock(&fw_cfg_dev_lock);
 
         acpi_release_global_lock(glk);
+        return count;
 }
 
 /* clean up fw_cfg device i/o */
@@ -183,8 +184,9 @@ static int fw_cfg_do_platform_probe(struct platform_device *pdev)
         }
 
         /* verify fw_cfg device signature */
-        fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, 0, FW_CFG_SIG_SIZE);
-        if (memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) {
+        if (fw_cfg_read_blob(FW_CFG_SIGNATURE, sig,
+                                0, FW_CFG_SIG_SIZE) < 0 ||
+                memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) {
                 fw_cfg_io_cleanup();
                 return -ENODEV;
         }
@@ -344,8 +346,7 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
         if (count > entry->size - pos)
                 count = entry->size - pos;
 
-        fw_cfg_read_blob(entry->select, buf, pos, count);
-        return count;
+        return fw_cfg_read_blob(entry->select, buf, pos, count);
 }
 
 static struct bin_attribute fw_cfg_sysfs_attr_raw = {
@@ -501,7 +502,11 @@ static int fw_cfg_register_dir_entries(void)
         struct fw_cfg_file *dir;
         size_t dir_size;
 
-        fw_cfg_read_blob(FW_CFG_FILE_DIR, &files_count, 0, sizeof(files_count));
+        ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, &files_count,
+                        0, sizeof(files_count));
+        if (ret < 0)
+                return ret;
+
         count = be32_to_cpu(files_count);
         dir_size = count * sizeof(struct fw_cfg_file);
 
@@ -509,7 +514,10 @@ static int fw_cfg_register_dir_entries(void)
         if (!dir)
                 return -ENOMEM;
 
-        fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(files_count), dir_size);
+        ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, dir,
+                        sizeof(files_count), dir_size);
+        if (ret < 0)
+                goto end;
 
         for (i = 0; i < count; i++) {
                 ret = fw_cfg_register_file(&dir[i]);
@@ -517,6 +525,7 @@ static int fw_cfg_register_dir_entries(void)
                         break;
         }
 
+end:
         kfree(dir);
         return ret;
 }
@@ -557,7 +566,10 @@ static int fw_cfg_sysfs_probe(struct platform_device *pdev)
                 goto err_probe;
 
         /* get revision number, add matching top-level attribute */
-        fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev));
+        err = fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev));
+        if (err < 0)
+                goto err_probe;
+
         fw_cfg_rev = le32_to_cpu(rev);
         err = sysfs_create_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
         if (err)