net/mlx5: fix uaccess beyond "count" in debugfs read/write 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.

For the read handlers, fix it by using simple_read_from_buffer() instead of
custom logic.
For the write handler, add a check.

changed in v2:
 - also fix dbg_write()

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: Saeed Mahameed <saeedm@mellanox.com>

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
index 3cb629e..a949553 100644 (file)
--- a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
@@ -1032,7 +1032,10 @@ static ssize_t dbg_write(struct file *filp, const char __user *buf,
        if (!dbg->in_msg || !dbg->out_msg)
                return -ENOMEM;
 
-       if (copy_from_user(lbuf, buf, sizeof(lbuf)))
+       if (count < sizeof(lbuf) - 1)
+               return -EINVAL;
+
+       if (copy_from_user(lbuf, buf, sizeof(lbuf) - 1))
                return -EFAULT;
 
        lbuf[sizeof(lbuf) - 1] = 0;
@@ -1236,21 +1239,12 @@ 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 = {
@@ -1268,19 +1262,11 @@ 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 413080a..90fabd6 100644 (file)
--- 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 = {