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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Michal Suchanek <msuchanek@suse.com>,
        Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Sasha Levin <alexander.levin@microsoft.com>
Subject: [PATCH 4.18 127/197] powerpc/pseries: Avoid using the size greater than RTAS_ERROR_LOG_MAX.
Date:   Thu, 13 Sep 2018 15:31:16 +0200
Message-Id: <20180913131846.624968166@linuxfoundation.org>
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4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>

[ Upstream commit 74e96bf44f430cf7a01de19ba6cf49b361cdfd6e ]

The global mce data buffer that used to copy rtas error log is of 2048
(RTAS_ERROR_LOG_MAX) bytes in size. Before the copy we read
extended_log_length from rtas error log header, then use max of
extended_log_length and RTAS_ERROR_LOG_MAX as a size of data to be copied.
Ideally the platform (phyp) will never send extended error log with
size > 2048. But if that happens, then we have a risk of buffer overrun
and corruption. Fix this by using min_t instead.

Fixes: d368514c3097 ("powerpc: Fix corruption when grabbing FWNMI data")
Reported-by: Michal Suchanek <msuchanek@suse.com>
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/powerpc/platforms/pseries/ras.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/powerpc/platforms/pseries/ras.c
+++ b/arch/powerpc/platforms/pseries/ras.c
@@ -371,7 +371,7 @@ static struct rtas_error_log *fwnmi_get_
 		int len, error_log_length;
 
 		error_log_length = 8 + rtas_error_extended_log_length(h);
-		len = max_t(int, error_log_length, RTAS_ERROR_LOG_MAX);
+		len = min_t(int, error_log_length, RTAS_ERROR_LOG_MAX);
 		memset(global_mce_data_buf, 0, RTAS_ERROR_LOG_MAX);
 		memcpy(global_mce_data_buf, h, len);
 		errhdr = (struct rtas_error_log *)global_mce_data_buf;