Vulnerability CVE-2023-52733
Published: 2024-05-21

Description:
In the Linux kernel, the following vulnerability has been resolved:

s390/decompressor: specify __decompress() buf len to avoid overflow

Historically calls to __decompress() didn't specify "out_len" parameter
on many architectures including s390, expecting that no writes beyond
uncompressed kernel image are performed. This has changed since commit
2aa14b1ab2c4 ("zstd: import usptream v1.5.2") which includes zstd library
commit 6a7ede3dfccb ("Reduce size of dctx by reutilizing dst buffer
(#2751)"). Now zstd decompression code might store literal buffer in
the unwritten portion of the destination buffer. Since "out_len" is
not set, it is considered to be unlimited and hence free to use for
optimization needs. On s390 this might corrupt initrd or ipl report
which are often placed right after the decompressor buffer. Luckily the
size of uncompressed kernel image is already known to the decompressor,
so to avoid the problem simply specify it in the "out_len" parameter.

 References:
https://git.kernel.org/stable/c/16409f7d9ca5bb8220e1049ea9aae0d3c94d2dfb
https://git.kernel.org/stable/c/55dbd6f4ea954751340f4f73d5dcd7c8f12208b2
https://git.kernel.org/stable/c/9ed522143f959630f8b7782ddc212900d8f609a9
https://git.kernel.org/stable/c/f1eb22d0ff064ad458b3b1a1eaa84ac3996206c2
https://git.kernel.org/stable/c/7ab41c2c08a32132ba8c14624910e2fe8ce4ba4b
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