Btrfs: rework error handling in btrfs_mount()

Commits 6c41761f and 45ea6095 introduced the possibility of NULL pointer
dereference on error paths, also we would leave all devices busy and
leak fs_info with all sub-structures on error when trying to mount an
already mounted fs to a different directory.

Fix this by doing all allocations before trying to open any of the
devices, adjust error path for mount-already-mounted-fs case.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

1 files changed, 21 insertions, 21 deletions

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 58e9492230ce..629281c65ff5 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -891,7 +891,6 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
         struct super_block *s;
         struct dentry *root;
         struct btrfs_fs_devices *fs_devices = NULL;
-        struct btrfs_root *tree_root = NULL;
         struct btrfs_fs_info *fs_info = NULL;
         fmode_t mode = FMODE_READ;
         char *subvol_name = NULL;
@@ -920,15 +919,6 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
         if (error)
                 return ERR_PTR(error);
 
-        error = btrfs_open_devices(fs_devices, mode, fs_type);
-        if (error)
-                return ERR_PTR(error);
-
-        if (!(flags & MS_RDONLY) && fs_devices->rw_devices == 0) {
-                error = -EACCES;
-                goto error_close_devices;
-        }
-
         /*
          * Setup a dummy root and fs_info for test/set super.  This is because
          * we don't actually fill this stuff out until open_ctree, but we need
@@ -936,28 +926,36 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
          * then open_ctree will properly initialize everything later.
          */
         fs_info = kzalloc(sizeof(struct btrfs_fs_info), GFP_NOFS);
-        if (!fs_info) {
-                error = -ENOMEM;
-                goto error_close_devices;
-        }
-        tree_root = kzalloc(sizeof(struct btrfs_root), GFP_NOFS);
-        if (!tree_root) {
+        if (!fs_info)
+                return ERR_PTR(-ENOMEM);
+
+        fs_info->tree_root = kzalloc(sizeof(struct btrfs_root), GFP_NOFS);
+        if (!fs_info->tree_root) {
                 error = -ENOMEM;
-                goto error_close_devices;
+                goto error_fs_info;
         }
-        fs_info->tree_root = tree_root;
+        fs_info->tree_root->fs_info = fs_info;
         fs_info->fs_devices = fs_devices;
-        tree_root->fs_info = fs_info;
 
         fs_info->super_copy = kzalloc(BTRFS_SUPER_INFO_SIZE, GFP_NOFS);
         fs_info->super_for_commit = kzalloc(BTRFS_SUPER_INFO_SIZE, GFP_NOFS);
         if (!fs_info->super_copy || !fs_info->super_for_commit) {
                 error = -ENOMEM;
+                goto error_fs_info;
+        }
+
+        error = btrfs_open_devices(fs_devices, mode, fs_type);
+        if (error)
+                goto error_fs_info;
+
+        if (!(flags & MS_RDONLY) && fs_devices->rw_devices == 0) {
+                error = -EACCES;
                 goto error_close_devices;
         }
 
         bdev = fs_devices->latest_bdev;
-        s = sget(fs_type, btrfs_test_super, btrfs_set_super, tree_root);
+        s = sget(fs_type, btrfs_test_super, btrfs_set_super,
+                 fs_info->tree_root);
         if (IS_ERR(s)) {
                 error = PTR_ERR(s);
                 goto error_close_devices;
@@ -966,7 +964,8 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
         if (s->s_root) {
                 if ((flags ^ s->s_flags) & MS_RDONLY) {
                         deactivate_locked_super(s);
-                        return ERR_PTR(-EBUSY);
+                        error = -EBUSY;
+                        goto error_close_devices;
                 }
 
                 btrfs_close_devices(fs_devices);
@@ -997,6 +996,7 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
 
 error_close_devices:
         btrfs_close_devices(fs_devices);
+error_fs_info:
         free_fs_info(fs_info);
         return ERR_PTR(error);
 }