FS: JFS: Fix null-ptr-deref Read in txBegin

stable inclusion
from stable-v5.10.192
commit 2a3f20efe6c901d4c0871cfd1d8c65e2ade71fc1
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I933RF

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2a3f20efe6c901d4c0871cfd1d8c65e2ade71fc1



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

[ Upstream commit 47cfdc33 ]

 Syzkaller reported an issue where txBegin may be called
 on a superblock in a read-only mounted filesystem which leads
 to NULL pointer deref. This could be solved by checking if
 the filesystem is read-only before calling txBegin, and returning
 with appropiate error code.

Reported-By:  <syzbot+f1faa20eec55e0c8644c@syzkaller.appspotmail.com>
Link: https://syzkaller.appspot.com/bug?id=be7e52c50c5182cc09a09ea6fc456446b2039de3



Signed-off-by: Immad Mir <mirimmad17@gmail.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>