lkml.org 
[lkml]   [2019]   [Jan]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH 2/8] libertas: change snprintf to scnprintf for possible overflow
On Sat, Jan 12, 2019 at 7:28 AM Willy Tarreau <w@1wt.eu> wrote:
>
> From: Silvio Cesare <silvio.cesare@gmail.com>
>
> Change snprintf to scnprintf. There are generally two cases where using
> snprintf causes problems.
>
> 1) Uses of size += snprintf(buf, SIZE - size, fmt, ...)
> In this case, if snprintf would have written more characters than what the
> buffer size (SIZE) is, then size will end up larger than SIZE. In later
> uses of snprintf, SIZE - size will result in a negative number, leading
> to problems. Note that size might already be too large by using
> size = snprintf before the code reaches a case of size += snprintf.
>
> 2) If size is ultimately used as a length parameter for a copy back to user
> space, then it will potentially allow for a buffer overflow and information
> disclosure when size is greater than SIZE. When the size is used to index
> the buffer directly, we can have memory corruption. This also means when
> size = snprintf... is used, it may also cause problems since size may become
> large. Copying to userspace is mitigated by the HARDENED_USERCOPY kernel
> configuration.
>
> The solution to these issues is to use scnprintf which returns the number of
> characters actually written to the buffer, so the size variable will never
> exceed SIZE.
>
> Signed-off-by: Silvio Cesare <silvio.cesare@gmail.com>
> Cc: Kalle Valo <kvalo@codeaurora.org>
> Cc: Dan Carpenter <dan.carpenter@oracle.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Greg KH <greg@kroah.com>
> Signed-off-by: Willy Tarreau <w@1wt.eu>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

>
> ---
> drivers/net/wireless/marvell/libertas/debugfs.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/net/wireless/marvell/libertas/debugfs.c b/drivers/net/wireless/marvell/libertas/debugfs.c
> index c83f44f9ddf1..ec73bd3a10db 100644
> --- a/drivers/net/wireless/marvell/libertas/debugfs.c
> +++ b/drivers/net/wireless/marvell/libertas/debugfs.c
> @@ -41,9 +41,9 @@ static ssize_t lbs_dev_info(struct file *file, char __user *userbuf,
> if (!buf)
> return -ENOMEM;
>
> - pos += snprintf(buf+pos, len-pos, "state = %s\n",
> + pos += scnprintf(buf+pos, len-pos, "state = %s\n",
> szStates[priv->connect_status]);
> - pos += snprintf(buf+pos, len-pos, "region_code = %02x\n",
> + pos += scnprintf(buf+pos, len-pos, "region_code = %02x\n",
> (u32) priv->regioncode);
>
> res = simple_read_from_buffer(userbuf, count, ppos, buf, pos);
> @@ -105,7 +105,7 @@ static ssize_t lbs_sleepparams_read(struct file *file, char __user *userbuf,
> if (ret)
> goto out_unlock;
>
> - pos += snprintf(buf, len, "%d %d %d %d %d %d\n", sp.sp_error,
> + pos += scnprintf(buf, len, "%d %d %d %d %d %d\n", sp.sp_error,
> sp.sp_offset, sp.sp_stabletime,
> sp.sp_calcontrol, sp.sp_extsleepclk,
> sp.sp_reserved);
> @@ -170,7 +170,7 @@ static ssize_t lbs_host_sleep_read(struct file *file, char __user *userbuf,
> if (!buf)
> return -ENOMEM;
>
> - pos += snprintf(buf, len, "%d\n", priv->is_host_sleep_activated);
> + pos += scnprintf(buf, len, "%d\n", priv->is_host_sleep_activated);
>
> ret = simple_read_from_buffer(userbuf, count, ppos, buf, pos);
>
> @@ -251,7 +251,7 @@ static ssize_t lbs_threshold_read(uint16_t tlv_type, uint16_t event_mask,
> freq = got->freq;
> events = le16_to_cpu(subscribed->events);
>
> - pos += snprintf(buf, len, "%d %d %d\n", value, freq,
> + pos += scnprintf(buf, len, "%d %d %d\n", value, freq,
> !!(events & event_mask));
> }
>
> @@ -446,7 +446,7 @@ static ssize_t lbs_rdmac_read(struct file *file, char __user *userbuf,
> ret = lbs_get_reg(priv, CMD_MAC_REG_ACCESS, priv->mac_offset, &val);
> mdelay(10);
> if (!ret) {
> - pos = snprintf(buf, len, "MAC[0x%x] = 0x%08x\n",
> + pos = scnprintf(buf, len, "MAC[0x%x] = 0x%08x\n",
> priv->mac_offset, val);
> ret = simple_read_from_buffer(userbuf, count, ppos, buf, pos);
> }
> @@ -516,7 +516,7 @@ static ssize_t lbs_rdbbp_read(struct file *file, char __user *userbuf,
> ret = lbs_get_reg(priv, CMD_BBP_REG_ACCESS, priv->bbp_offset, &val);
> mdelay(10);
> if (!ret) {
> - pos = snprintf(buf, len, "BBP[0x%x] = 0x%08x\n",
> + pos = scnprintf(buf, len, "BBP[0x%x] = 0x%08x\n",
> priv->bbp_offset, val);
> ret = simple_read_from_buffer(userbuf, count, ppos, buf, pos);
> }
> @@ -588,7 +588,7 @@ static ssize_t lbs_rdrf_read(struct file *file, char __user *userbuf,
> ret = lbs_get_reg(priv, CMD_RF_REG_ACCESS, priv->rf_offset, &val);
> mdelay(10);
> if (!ret) {
> - pos = snprintf(buf, len, "RF[0x%x] = 0x%08x\n",
> + pos = scnprintf(buf, len, "RF[0x%x] = 0x%08x\n",
> priv->rf_offset, val);
> ret = simple_read_from_buffer(userbuf, count, ppos, buf, pos);
> }
> --
> 2.19.2
>


--
Kees Cook

\
 
 \ /
  Last update: 2019-01-15 02:10    [W:0.421 / U:0.324 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site