linux-kernel - [PATCH AUTOSEL 5.10 11/13] s390/decompressor: specify _

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Date:   Thu,  9 Feb 2023 06:18:29 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Egorenkov <egorenar@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Sasha Levin <sashal@...nel.org>, agordeev@...ux.ibm.com,
        terrelln@...com, linux-s390@...r.kernel.org
Subject: [PATCH AUTOSEL 5.10 11/13] s390/decompressor: specify __decompress() buf len to avoid overflow

From: Vasily Gorbik <gor@...ux.ibm.com>

[ Upstream commit 7ab41c2c08a32132ba8c14624910e2fe8ce4ba4b ]

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.

Link: https://github.com/facebook/zstd/commit/6a7ede3dfccb
Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
Tested-by: Alexander Egorenkov <egorenar@...ux.ibm.com>
Link: https://lore.kernel.org/r/patch-1.thread-41c676.git-41c676c2d153.your-ad-here.call-01675030179-ext-9637@work.hours
Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/s390/boot/compressed/decompressor.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/boot/compressed/decompressor.c b/arch/s390/boot/compressed/decompressor.c
index 3061b11c4d27f..8eaa1712a1c8d 100644
--- a/arch/s390/boot/compressed/decompressor.c
+++ b/arch/s390/boot/compressed/decompressor.c
@@ -79,6 +79,6 @@ void *decompress_kernel(void)
 	void *output = (void *)decompress_offset;

 	__decompress(_compressed_start, _compressed_end - _compressed_start,
-		     NULL, NULL, output, 0, NULL, error);
+		     NULL, NULL, output, vmlinux.image_size, NULL, error);
 	return output;
 }
-- 
2.39.0