xz: avoid overlapping memcpy() with invalid input with in-place decompression

xz: avoid overlapping memcpy() with invalid input with in-place decompression

From: Lasse Collin <lasse.collin@tukaani.org>

With valid files, the safety margin described in lib/decompress_unxz.c
ensures that these buffers cannot overlap. But if the uncompressed size
of the input is larger than the caller thought, which is possible when
the input file is invalid/corrupt, the buffers can overlap. Obviously
the result will then be garbage (and usually the decoder will return
an error too) but no other harm will happen when such an over-run occurs.

This change only affects uncompressed LZMA2 chunks and so this
should have no effect on performance.

Link: https://lore.kernel.org/r/20211010213145.17462-2-xiang@kernel.org
Signed-off-by: Lasse Collin <lasse.collin@tukaani.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Origin: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 83d3c4f22a36
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>