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Date:   Thu, 28 May 2020 15:37:03 +0300
From:   Dan Carpenter <dan.carpenter@oracle.com>
To:     Zhou Wang <wangzhou1@hisilicon.com>
Cc:     Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-janitors@vger.kernel.org
Subject: [PATCH] crypto: hisilicon/qm - allow smaller reads in debugfs
Message-ID: <20200528123703.GA1219412@mwanda>
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Sender: linux-crypto-owner@vger.kernel.org
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Originally this code rejected any read less than 256 bytes.  There
is no need for this artificial limit.

Also I have changed the snprintf() functions to scnprintf().  The
difference is that snprintf() returns the number of bytes which would
have been copied if there were enough space and scnprintf() returns the
number of bytes which were actually copied.  It doesn't matter here
because the strings are very short so they can't go over 256 bytes.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
 drivers/crypto/hisilicon/qm.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/drivers/crypto/hisilicon/qm.c b/drivers/crypto/hisilicon/qm.c
index a781c02251980..9c0c9f500d91d 100644
--- a/drivers/crypto/hisilicon/qm.c
+++ b/drivers/crypto/hisilicon/qm.c
@@ -1076,16 +1076,15 @@ static ssize_t qm_cmd_read(struct file *filp, char __user *buffer,
 	if (*pos)
 		return 0;
 
-	if (count < QM_DBG_READ_LEN)
-		return -ENOSPC;
-
-	len = snprintf(buf, QM_DBG_READ_LEN, "%s\n",
+	len = scnprintf(buf, QM_DBG_READ_LEN, "%s\n",
 		       "Please echo help to cmd to get help information");
 
+	len = min_t(size_t, len, count);
 	if (copy_to_user(buffer, buf, len))
 		return -EFAULT;
 
-	return (*pos = len);
+	*pos = len;
+	return len;
 }
 
 static void *qm_ctx_alloc(struct hisi_qm *qm, size_t ctx_size,
@@ -2710,19 +2709,18 @@ static ssize_t qm_status_read(struct file *filp, char __user *buffer,
 	if (*pos)
 		return 0;
 
-	if (count < QM_DBG_READ_LEN)
-		return -ENOSPC;
-
 	val = atomic_read(&qm->status.flags);
-	len = snprintf(buf, QM_DBG_READ_LEN, "%s\n", qm_s[val]);
+	len = scnprintf(buf, QM_DBG_READ_LEN, "%s\n", qm_s[val]);
 	if (!len)
 		return -EFAULT;
 
+	len = min_t(size_t, len, count);
 	cp_len = copy_to_user(buffer, buf, len);
 	if (cp_len)
 		return -EFAULT;
 
-	return (*pos = len);
+	*pos = len;
+	return len;
 }
 
 static const struct file_operations qm_status_fops = {
-- 
2.26.2