btrfs: send: limit number of clones and allocated memory size

stable inclusion
from stable-v5.10.171
commit 6195cea4c738146f6665f71944325766daef1a5f
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7V9QX

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6195cea4c738146f6665f71944325766daef1a5f



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[ Upstream commit 33e17b3f ]

The arg->clone_sources_count is u64 and can trigger a warning when a
huge value is passed from user space and a huge array is allocated.
Limit the allocated memory to 8MiB (can be increased if needed), which
in turn limits the number of clone sources to 8M / sizeof(struct
clone_root) = 8M / 40 = 209715.  Real world number of clones is from
tens to hundreds, so this is future proof.

Reported-by:  <syzbot+4376a9a073770c173269@syzkaller.appspotmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: zhaoxiaoqiang11 <zhaoxiaoqiang11@jd.com>