Re: [PATCH 1/2] ext4: alloc test super block from sget

[Christian Brauner <brauner@kernel.org>]

On Fri, Mar 01, 2024 at 09:25:59AM +0100, Christian Brauner wrote:
> On Fri, Mar 01, 2024 at 08:08:15PM +0800, Kemeng Shi wrote:
> > This fix the oops in ext4 unit test which is cuased by NULL sb.s_user_ns
> > as following:
> > <4>[ 14.344565] map_id_range_down (kernel/user_namespace.c:318)
> > <4>[ 14.345378] make_kuid (kernel/user_namespace.c:415)
> > <4>[ 14.345998] inode_init_always (include/linux/fs.h:1375 fs/inode.c:174)
> > <4>[ 14.346696] alloc_inode (fs/inode.c:268)
> > <4>[ 14.347353] new_inode_pseudo (fs/inode.c:1007)
> > <4>[ 14.348016] new_inode (fs/inode.c:1033)
> > <4>[ 14.348644] ext4_mb_init (fs/ext4/mballoc.c:3404 fs/ext4/mballoc.c:3719)
> > <4>[ 14.349312] mbt_kunit_init (fs/ext4/mballoc-test.c:57
> > fs/ext4/mballoc-test.c:314)
> > <4>[ 14.349983] kunit_try_run_case (lib/kunit/test.c:388 lib/kunit/test.c:443)
> > <4>[ 14.350696] kunit_generic_run_threadfn_adapter (lib/kunit/try-catch.c:30)
> > <4>[ 14.351530] kthread (kernel/kthread.c:388)
> > <4>[ 14.352168] ret_from_fork (arch/arm64/kernel/entry.S:861)
> > <0>[ 14.353385] Code: 52808004 b8236ae7 72be5e44 b90004c4 (38e368a1)
> > 
> > Alloc test super block from sget to properly initialize test super block
> > to fix the issue.
> > 
> > Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
> > Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> > Reported-by: Guenter Roeck <linux@roeck-us.net>
> > ---
> >  fs/ext4/mballoc-test.c | 46 ++++++++++++++++++++++++++++--------------
> >  1 file changed, 31 insertions(+), 15 deletions(-)
> > 
> > diff --git a/fs/ext4/mballoc-test.c b/fs/ext4/mballoc-test.c
> > index 12d0b22cabe1..1da52bbf4599 100644
> > --- a/fs/ext4/mballoc-test.c
> > +++ b/fs/ext4/mballoc-test.c
> > @@ -21,16 +21,27 @@ struct mbt_ctx {
> >  };
> >  
> >  struct mbt_ext4_super_block {
> > -	struct super_block sb;
> > +	struct ext4_super_block es;
> > +	struct ext4_sb_info sbi;
> >  	struct mbt_ctx mbt_ctx;
> >  };
> >  
> > -#define MBT_CTX(_sb) (&(container_of((_sb), struct mbt_ext4_super_block, sb)->mbt_ctx))
> > +#define MBT_SB(_sb) (container_of((_sb)->s_fs_info, struct mbt_ext4_super_block, sbi))
> > +#define MBT_CTX(_sb) (&MBT_SB(_sb)->mbt_ctx)
> >  #define MBT_GRP_CTX(_sb, _group) (&MBT_CTX(_sb)->grp_ctx[_group])
> >  
> >  static const struct super_operations mbt_sops = {
> >  };
> >  
> > +static void mbt_kill_sb(struct super_block *sb)
> > +{
> > +}
> > +
> > +static struct file_system_type mbt_fs_type = {
> > +	.name			= "mballoc test",
> > +	.kill_sb		= mbt_kill_sb,
> > +};
> > +
> >  static int mbt_mb_init(struct super_block *sb)
> >  {
> >  	int ret;
> > @@ -72,43 +83,48 @@ static void mbt_mb_release(struct super_block *sb)
> >  	kfree(sb->s_bdev);
> >  }
> >  
> > +static int mbt_set(struct super_block *sb, void *data)
> > +{
> > +	return 0;
> > +}
> > +
> >  static struct super_block *mbt_ext4_alloc_super_block(void)
> >  {
> > -	struct ext4_super_block *es = kzalloc(sizeof(*es), GFP_KERNEL);
> > -	struct ext4_sb_info *sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> >  	struct mbt_ext4_super_block *fsb = kzalloc(sizeof(*fsb), GFP_KERNEL);
> > +	struct super_block *sb = sget(&mbt_fs_type, NULL, mbt_set, 0, NULL);
> > +	struct ext4_sb_info *sbi;
> >  
> > -	if (fsb == NULL || sbi == NULL || es == NULL)
> > +	if (fsb == NULL || sb == NULL)
> 
> sget() returns error pointer on failure. So you should check for IS_ERR(sb).

You also want to unlock that superblock up_write(sb->s_umount) if it
succeeded and then call deactivate_super() when you are done with it in
mbt_kunit_exit().