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From:   Yi Zhuang <zhuangyi1@huawei.com>
To:     <benh@kernel.crashing.org>, <paulus@samba.org>
CC:     <zhuangyi1@huawei.com>, <hegdevasant@linux.vnet.ibm.com>,
        <mpe@ellerman.id.au>, <linuxppc-dev@lists.ozlabs.org>,
        <linux-kernel@vger.kernel.org>
Subject: [PATCH] powerpc/rtas_flash: fix a potential buffer overflow
Date:   Wed, 14 Jul 2021 09:16:08 +0800
Message-ID: <20210714011608.15043-1-zhuangyi1@huawei.com>
MIME-Version: 1.0
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Precedence: bulk

Since snprintf() returns the possible output size instead of the
actual output size, the available flash_msg length returned by
get_validate_flash_msg may exceed the given buffer limit when
simple_read_from_buffer calls copy_to_user

Signed-off-by: Yi Zhuang <zhuangyi1@huawei.com>
---
 arch/powerpc/kernel/rtas_flash.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/kernel/rtas_flash.c b/arch/powerpc/kernel/rtas_flash.c
index a99179d83538..4aa6bad28556 100644
--- a/arch/powerpc/kernel/rtas_flash.c
+++ b/arch/powerpc/kernel/rtas_flash.c
@@ -473,6 +473,10 @@ static int get_validate_flash_msg(struct rtas_validate_flash_t *args_buf,
 		    (args_buf->update_results == VALIDATE_TMP_UPDATE))
 			n += snprintf(msg + n, msglen - n, "%s\n",
 					args_buf->buf);
+			if (n >= msglen) {
+				n = msglen;
+				printk(KERN_ERR "FLASH: msg too long.\n");
+			}
 	} else {
 		n = sprintf(msg, "%d\n", args_buf->status);
 	}
-- 
2.26.0.106.g9fadedd