fs: jfs: fix shift-out-of-bounds in dbAllocAG

stable inclusion
from stable-v5.10.163
commit 3e997e4ce8ae7ab89d72334120f6aee49c5bbdbd
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9RG40
CVE: CVE-2023-52804

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3e997e4ce8ae7ab89d72334120f6aee49c5bbdbd



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[ Upstream commit 898f7066 ]

Syzbot found a crash : UBSAN: shift-out-of-bounds in dbAllocAG. The
underlying bug is the missing check of bmp->db_agl2size. The field can
be greater than 64 and trigger the shift-out-of-bounds.

Fix this bug by adding a check of bmp->db_agl2size in dbMount since this
field is used in many following functions. The upper bound for this
field is L2MAXL2SIZE - L2MAXAG, thanks for the help of Dave Kleikamp.
Note that, for maintenance, I reorganized error handling code of dbMount.

Reported-by:  <syzbot+15342c1aa6a00fb7a438@syzkaller.appspotmail.com>
Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Wang Hai <wanghai38@huawei.com>
Signed-off-by: Yifan Qiao <qiaoyifan4@huawei.com>