Messages in this thread | | | From | Kees Cook <> | Date | Mon, 14 Jan 2019 17:09:05 -0800 | Subject | Re: [PATCH 2/8] libertas: change snprintf to scnprintf for possible overflow |
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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
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