fs/sysv: Null check to prevent null-ptr-deref bug

stable inclusion
from stable-v5.10.190
commit 7f740bc696d4617f8ee44565e8ac0d36278a1e91
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I928UI

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7f740bc696d4617f8ee44565e8ac0d36278a1e91



--------------------------------

commit ea2b62f3 upstream.

sb_getblk(inode->i_sb, parent) return a null ptr and taking lock on
that leads to the null-ptr-deref bug.

Reported-by:  <syzbot+aad58150cbc64ba41bdc@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=aad58150cbc64ba41bdc


Signed-off-by: Prince Kumar Maurya <princekumarmaurya06@gmail.com>
Message-Id: <20230531013141.19487-1-princekumarmaurya06@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>