fuse: always initialize sb->s_fs_info
Syzkaller reports a null pointer dereference in fuse_test_super() that is
caused by sb->s_fs_info being NULL.
This is due to the fact that fuse_fill_super() is initializing s_fs_info,
which is too late, it's already on the fs_supers list. The initialization
needs to be done in sget_fc() with the sb_lock held.
Move allocation of fuse_mount and fuse_conn from fuse_fill_super() into
fuse_get_tree().
After this ->kill_sb() will always be called with non-NULL ->s_fs_info,
hence fuse_mount_destroy() can drop the test for non-NULL "fm".
Reported-by: syzbot+74a15f02ccb51f398601@syzkaller.appspotmail.com
Fixes: 5d5b74aa9c76 ("fuse: allow sharing existing sb")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 308daee..b468f55 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1557,8 +1557,6 @@
{
struct fuse_fs_context *ctx = fsc->fs_private;
int err;
- struct fuse_conn *fc;
- struct fuse_mount *fm;
if (!ctx->file || !ctx->rootmode_present ||
!ctx->user_id_present || !ctx->group_id_present)
@@ -1574,22 +1572,6 @@
goto err;
ctx->fudptr = &ctx->file->private_data;
- fc = kmalloc(sizeof(*fc), GFP_KERNEL);
- err = -ENOMEM;
- if (!fc)
- goto err;
-
- fm = kzalloc(sizeof(*fm), GFP_KERNEL);
- if (!fm) {
- kfree(fc);
- goto err;
- }
-
- fuse_conn_init(fc, fm, sb->s_user_ns, &fuse_dev_fiq_ops, NULL);
- fc->release = fuse_free_conn;
-
- sb->s_fs_info = fm;
-
err = fuse_fill_super_common(sb, ctx);
if (err)
goto err;
@@ -1621,22 +1603,40 @@
{
struct fuse_fs_context *ctx = fsc->fs_private;
struct fuse_dev *fud;
+ struct fuse_conn *fc;
+ struct fuse_mount *fm;
struct super_block *sb;
int err;
+ fc = kmalloc(sizeof(*fc), GFP_KERNEL);
+ if (!fc)
+ return -ENOMEM;
+
+ fm = kzalloc(sizeof(*fm), GFP_KERNEL);
+ if (!fm) {
+ kfree(fc);
+ return -ENOMEM;
+ }
+
+ fuse_conn_init(fc, fm, fsc->user_ns, &fuse_dev_fiq_ops, NULL);
+ fc->release = fuse_free_conn;
+
+ fsc->s_fs_info = fm;
+
if (ctx->fd_present)
ctx->file = fget(ctx->fd);
if (IS_ENABLED(CONFIG_BLOCK) && ctx->is_bdev) {
err = get_tree_bdev(fsc, fuse_fill_super);
- goto out_fput;
+ goto out;
}
/*
* While block dev mount can be initialized with a dummy device fd
* (found by device name), normal fuse mounts can't
*/
+ err = -EINVAL;
if (!ctx->file)
- return -EINVAL;
+ goto out;
/*
* Allow creating a fuse mount with an already initialized fuse
@@ -1652,7 +1652,9 @@
} else {
err = get_tree_nodev(fsc, fuse_fill_super);
}
-out_fput:
+out:
+ if (fsc->s_fs_info)
+ fuse_mount_destroy(fm);
if (ctx->file)
fput(ctx->file);
return err;
@@ -1740,10 +1742,8 @@
void fuse_mount_destroy(struct fuse_mount *fm)
{
- if (fm) {
- fuse_conn_put(fm->fc);
- kfree(fm);
- }
+ fuse_conn_put(fm->fc);
+ kfree(fm);
}
EXPORT_SYMBOL(fuse_mount_destroy);
