iommu/omap: Fix buffer overflow in debugfs

stable inclusion
from stable-v5.10.150
commit 2fee0dbfaeaaa4bda04279ce772c4572b1429d04
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6D0XA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2fee0dbfaeaaa4bda04279ce772c4572b1429d04



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[ Upstream commit 184233a5 ]

There are two issues here:

1) The "len" variable needs to be checked before the very first write.
   Otherwise if omap2_iommu_dump_ctx() with "bytes" less than 32 it is a
   buffer overflow.
2) The snprintf() function returns the number of bytes that *would* have
   been copied if there were enough space.  But we want to know the
   number of bytes which were *actually* copied so use scnprintf()
   instead.

Fixes: bd4396f0 ("iommu/omap: Consolidate OMAP IOMMU modules")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/YuvYh1JbE3v+abd5@kili


Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>