netdev - [PATCH net] net/mlx5: fix uaccess beyond "count" in debugfs read handlers

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Message-Id: <20180706152028.31775-1-jannh@google.com>
Date:   Fri,  6 Jul 2018 17:20:28 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Saeed Mahameed <saeedm@...lanox.com>,
        Leon Romanovsky <leon@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, jannh@...gle.com
Cc:     netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH net] net/mlx5: fix uaccess beyond "count" in debugfs read handlers

In general, accessing userspace memory beyond the length of the supplied
buffer in VFS read/write handlers can lead to both kernel memory corruption
(via kernel_read()/kernel_write(), which can e.g. be triggered via
sys_splice()) and privilege escalation inside userspace.

In this case, the affected files are in debugfs (and should therefore only
be accessible to root) and check that *pos is zero (which prevents the
sys_splice() trick). Therefore, this is not a security fix, but rather a
small cleanup.

Fix it by using simple_read_from_buffer() instead of custom logic.

Fixes: e126ba97dba9 ("mlx5: Add driver for Mellanox Connect-IB adapters")
Signed-off-by: Jann Horn <jannh@...gle.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/cmd.c | 23 +++----------------
 .../net/ethernet/mellanox/mlx5/core/debugfs.c | 22 ++----------------
 2 files changed, 5 insertions(+), 40 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
index 384c1fa49081..0a79a4540923 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
@@ -1226,21 +1226,12 @@ static ssize_t data_read(struct file *filp, char __user *buf, size_t count,
 {
 	struct mlx5_core_dev *dev = filp->private_data;
 	struct mlx5_cmd_debug *dbg = &dev->cmd.dbg;
-	int copy;
-
-	if (*pos)
-		return 0;
 
 	if (!dbg->out_msg)
 		return -ENOMEM;
 
-	copy = min_t(int, count, dbg->outlen);
-	if (copy_to_user(buf, dbg->out_msg, copy))
-		return -EFAULT;
-
-	*pos += copy;
-
-	return copy;
+	return simple_read_from_buffer(buf, count, pos, dbg->out_msg,
+				       dbg->outlen);
 }
 
 static const struct file_operations dfops = {
@@ -1258,19 +1249,11 @@ static ssize_t outlen_read(struct file *filp, char __user *buf, size_t count,
 	char outlen[8];
 	int err;
 
-	if (*pos)
-		return 0;
-
 	err = snprintf(outlen, sizeof(outlen), "%d", dbg->outlen);
 	if (err < 0)
 		return err;
 
-	if (copy_to_user(buf, &outlen, err))
-		return -EFAULT;
-
-	*pos += err;
-
-	return err;
+	return simple_read_from_buffer(buf, count, pos, outlen, err);
 }
 
 static ssize_t outlen_write(struct file *filp, const char __user *buf,
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/debugfs.c b/drivers/net/ethernet/mellanox/mlx5/core/debugfs.c
index 413080a312a7..90fabd612b6c 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/debugfs.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/debugfs.c
@@ -150,22 +150,13 @@ static ssize_t average_read(struct file *filp, char __user *buf, size_t count,
 	int ret;
 	char tbuf[22];
 
-	if (*pos)
-		return 0;
-
 	stats = filp->private_data;
 	spin_lock_irq(&stats->lock);
 	if (stats->n)
 		field = div64_u64(stats->sum, stats->n);
 	spin_unlock_irq(&stats->lock);
 	ret = snprintf(tbuf, sizeof(tbuf), "%llu\n", field);
-	if (ret > 0) {
-		if (copy_to_user(buf, tbuf, ret))
-			return -EFAULT;
-	}
-
-	*pos += ret;
-	return ret;
+	return simple_read_from_buffer(buf, count, pos, tbuf, ret);
 }
 
 static ssize_t average_write(struct file *filp, const char __user *buf,
@@ -442,9 +433,6 @@ static ssize_t dbg_read(struct file *filp, char __user *buf, size_t count,
 	u64 field;
 	int ret;
 
-	if (*pos)
-		return 0;
-
 	desc = filp->private_data;
 	d = (void *)(desc - desc->i) - sizeof(*d);
 	switch (d->type) {
@@ -470,13 +458,7 @@ static ssize_t dbg_read(struct file *filp, char __user *buf, size_t count,
 	else
 		ret = snprintf(tbuf, sizeof(tbuf), "0x%llx\n", field);
 
-	if (ret > 0) {
-		if (copy_to_user(buf, tbuf, ret))
-			return -EFAULT;
-	}
-
-	*pos += ret;
-	return ret;
+	return simple_read_from_buffer(buf, count, pos, tbuf, ret);
 }
 
 static const struct file_operations fops = {
-- 
2.18.0.399.gad0ab374a1-goog