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Subject[PATCH 4.18 227/235] IB/mlx5: fix uaccess beyond "count" in debugfs read/write handlers
Date
4.18-stable review patch.  If anyone has any objections, please let me know.

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

From: Jann Horn <jannh@google.com>

[ Upstream commit 60e6627f12a78203a093ca05b7bca15627747d81 ]

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 the read handlers check that *pos is zero
(meaning that at least sys_splice() can't trigger kernel memory
corruption). Because of the root requirement, this is not a security fix,
but rather a cleanup.

For the read handlers, fix it by using simple_read_from_buffer() instead
of custom logic. Add min() calls to the write handlers.

Fixes: 4a2da0b8c078 ("IB/mlx5: Add debug control parameters for congestion control")
Fixes: e126ba97dba9 ("mlx5: Add driver for Mellanox Connect-IB adapters")
Signed-off-by: Jann Horn <jannh@google.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/infiniband/hw/mlx5/cong.c | 9 +--------
drivers/infiniband/hw/mlx5/mr.c | 32 ++++++++------------------------
2 files changed, 9 insertions(+), 32 deletions(-)

--- a/drivers/infiniband/hw/mlx5/cong.c
+++ b/drivers/infiniband/hw/mlx5/cong.c
@@ -359,9 +359,6 @@ static ssize_t get_param(struct file *fi
int ret;
char lbuf[11];

- if (*pos)
- return 0;
-
ret = mlx5_ib_get_cc_params(param->dev, param->port_num, offset, &var);
if (ret)
return ret;
@@ -370,11 +367,7 @@ static ssize_t get_param(struct file *fi
if (ret < 0)
return ret;

- if (copy_to_user(buf, lbuf, ret))
- return -EFAULT;
-
- *pos += ret;
- return ret;
+ return simple_read_from_buffer(buf, count, pos, lbuf, ret);
}

static const struct file_operations dbg_cc_fops = {
--- a/drivers/infiniband/hw/mlx5/mr.c
+++ b/drivers/infiniband/hw/mlx5/mr.c
@@ -271,16 +271,16 @@ static ssize_t size_write(struct file *f
{
struct mlx5_cache_ent *ent = filp->private_data;
struct mlx5_ib_dev *dev = ent->dev;
- char lbuf[20];
+ char lbuf[20] = {0};
u32 var;
int err;
int c;

- if (copy_from_user(lbuf, buf, sizeof(lbuf)))
+ count = min(count, sizeof(lbuf) - 1);
+ if (copy_from_user(lbuf, buf, count))
return -EFAULT;

c = order2idx(dev, ent->order);
- lbuf[sizeof(lbuf) - 1] = 0;

if (sscanf(lbuf, "%u", &var) != 1)
return -EINVAL;
@@ -310,19 +310,11 @@ static ssize_t size_read(struct file *fi
char lbuf[20];
int err;

- if (*pos)
- return 0;
-
err = snprintf(lbuf, sizeof(lbuf), "%d\n", ent->size);
if (err < 0)
return err;

- if (copy_to_user(buf, lbuf, err))
- return -EFAULT;
-
- *pos += err;
-
- return err;
+ return simple_read_from_buffer(buf, count, pos, lbuf, err);
}

static const struct file_operations size_fops = {
@@ -337,16 +329,16 @@ static ssize_t limit_write(struct file *
{
struct mlx5_cache_ent *ent = filp->private_data;
struct mlx5_ib_dev *dev = ent->dev;
- char lbuf[20];
+ char lbuf[20] = {0};
u32 var;
int err;
int c;

- if (copy_from_user(lbuf, buf, sizeof(lbuf)))
+ count = min(count, sizeof(lbuf) - 1);
+ if (copy_from_user(lbuf, buf, count))
return -EFAULT;

c = order2idx(dev, ent->order);
- lbuf[sizeof(lbuf) - 1] = 0;

if (sscanf(lbuf, "%u", &var) != 1)
return -EINVAL;
@@ -372,19 +364,11 @@ static ssize_t limit_read(struct file *f
char lbuf[20];
int err;

- if (*pos)
- return 0;
-
err = snprintf(lbuf, sizeof(lbuf), "%d\n", ent->limit);
if (err < 0)
return err;

- if (copy_to_user(buf, lbuf, err))
- return -EFAULT;
-
- *pos += err;
-
- return err;
+ return simple_read_from_buffer(buf, count, pos, lbuf, err);
}

static const struct file_operations limit_fops = {

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