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 <[email protected]>
---
drivers/net/ethernet/mellanox/mlx5/core/cmd.c | 28 +++++--------------
.../net/ethernet/mellanox/mlx5/core/debugfs.c | 22 ++-------------
2 files changed, 9 insertions(+), 41 deletions(-)
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
index 384c1fa49081..92578074145d 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
@@ -1022,7 +1022,10 @@ 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;
@@ -1226,21 +1229,12 @@ 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 +1252,11 @@ 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 = {
--
2.18.0.203.gfac676dfb9-goog
On Fri, Jul 06, 2018 at 10:18:09PM +0200, Jann Horn wrote:
> 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()
>
Thanks Jann,
Next time, please don't put changelog in commit message.
Saeed, are you taking it to mlx5-next? It is cleanup and better to be
sent to -next.
> Fixes: e126ba97dba9 ("mlx5: Add driver for Mellanox Connect-IB adapters")
> Signed-off-by: Jann Horn <[email protected]>
> ---
> drivers/net/ethernet/mellanox/mlx5/core/cmd.c | 28 +++++--------------
> .../net/ethernet/mellanox/mlx5/core/debugfs.c | 22 ++-------------
> 2 files changed, 9 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
Thanks,
Reviewed-by: Leon Romanovsky <[email protected]>
On Fri, 2018-07-06 at 22:18 +0200, Jann Horn wrote:
> 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 <[email protected]>
>
Applied to mlx5-next, Thanks!!