linux-kernel - [PATCH v3 1/2] lib: decompress

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Message-Id: <20200901142651.1165237-2-paul@crapouillou.net>
Date:   Tue,  1 Sep 2020 16:26:50 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Nick Terrell <terrelln@...com>
Cc:     od@...c.me, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paul Cercueil <paul@...pouillou.net>
Subject: [PATCH v3 1/2] lib: decompress_unzstd: Limit output size

The zstd decompression code, as it is right now, will most likely fail
on 32-bit systems, as the default output buffer size causes the buffer's
end address to overflow.

Address this issue by setting a sane default to the default output size,
with a value that won't overflow the buffer's end address.

Signed-off-by: Paul Cercueil <paul@...pouillou.net>
---

Notes:
    v2: Change limit to 1 GiB
    
    v3: Compute size limit instead of using hardcoded value

 lib/decompress_unzstd.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/lib/decompress_unzstd.c b/lib/decompress_unzstd.c
index 0ad2c15479ed..790abc472f5b 100644
--- a/lib/decompress_unzstd.c
+++ b/lib/decompress_unzstd.c
@@ -178,8 +178,13 @@ static int INIT __unzstd(unsigned char *in_buf, long in_len,
 	int err;
 	size_t ret;
 
+	/*
+	 * ZSTD decompression code won't be happy if the buffer size is so big
+	 * that its end address overflows. When the size is not provided, make
+	 * it as big as possible without having the end address overflow.
+	 */
 	if (out_len == 0)
-		out_len = LONG_MAX; /* no limit */
+		out_len = UINTPTR_MAX - (uintptr_t)out_buf;
 
 	if (fill == NULL && flush == NULL)
 		/*
-- 
2.28.0