Re: [PATCH v2 4/8] ASoC: imx-audmux: change snprintf to scnprintf for possible overflow
From: Gustavo A. R. Silva
Date: Mon Jan 14 2019 - 23:53:47 EST
Hi Willy,
On 1/14/19 9:27 PM, Willy Tarreau wrote:
From: Silvio Cesare <silvio.cesare@xxxxxxxxx>
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@xxxxxxxxx>
Cc: Timur Tabi <timur@xxxxxxxxxx>
Cc: Nicolin Chen <nicoleotsuka@xxxxxxxxx>
Cc: Mark Brown <broonie@xxxxxxxxxx>
Cc: Xiubo Li <Xiubo.Lee@xxxxxxxxx>
Cc: Fabio Estevam <fabio.estevam@xxxxxxx>
Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Greg KH <greg@xxxxxxxxx>
Signed-off-by: Willy Tarreau <w@xxxxxx>
Acked-by: Nicolin Chen <nicoleotsuka@xxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
You are still missing some people and mailing lists:
$ scripts/get_maintainer.pl --nokeywords --nogit --nogit-fallback sound/soc/fsl/imx-audmux.c
Timur Tabi <timur@xxxxxxxxxx> (maintainer:FREESCALE SOC SOUND DRIVERS)
Nicolin Chen <nicoleotsuka@xxxxxxxxx> (maintainer:FREESCALE SOC SOUND DRIVERS)
Xiubo Li <Xiubo.Lee@xxxxxxxxx> (maintainer:FREESCALE SOC SOUND DRIVERS)
Fabio Estevam <fabio.estevam@xxxxxxx> (reviewer:FREESCALE SOC SOUND DRIVERS)
Liam Girdwood <lgirdwood@xxxxxxxxx> (supporter:SOUND - SOC LAYER / DYNAMIC AUDIO POWER MANAGEM...)
Mark Brown <broonie@xxxxxxxxxx> (supporter:SOUND - SOC LAYER / DYNAMIC AUDIO POWER MANAGEM...)
Jaroslav Kysela <perex@xxxxxxxx> (maintainer:SOUND)
Takashi Iwai <tiwai@xxxxxxxx> (maintainer:SOUND)
Shawn Guo <shawnguo@xxxxxxxxxx> (maintainer:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE)
Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> (maintainer:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE)
Pengutronix Kernel Team <kernel@xxxxxxxxxxxxxx> (reviewer:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE)
NXP Linux Team <linux-imx@xxxxxxx> (reviewer:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE)
alsa-devel@xxxxxxxxxxxxxxxx (moderated list:FREESCALE SOC SOUND DRIVERS)
linuxppc-dev@xxxxxxxxxxxxxxxx (open list:FREESCALE SOC SOUND DRIVERS)
linux-arm-kernel@xxxxxxxxxxxxxxxxxxx (moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE)
linux-kernel@xxxxxxxxxxxxxxx (open list)
--
Gustavo
--
v2:
- adjust subject line
- added alsa-devel & Mark
- added acked-by
- added reviewed-by
The patches in this series were sent by Silvio to the security list
to fix a minor memory disclosure issue after this article was published:
http://blog.infosectcbr.com.au/2018/11/memory-bugs-in-multiple-linux-kernel.html
sound/soc/fsl/imx-audmux.c | 24 ++++++++++++------------
1 file changed, 12 insertions(+), 12 deletions(-)
diff --git a/sound/soc/fsl/imx-audmux.c b/sound/soc/fsl/imx-audmux.c
index 392d5eef356d..99e07b01a2ce 100644
--- a/sound/soc/fsl/imx-audmux.c
+++ b/sound/soc/fsl/imx-audmux.c
@@ -86,49 +86,49 @@ static ssize_t audmux_read_file(struct file *file, char __user *user_buf,
if (!buf)
return -ENOMEM;
- ret = snprintf(buf, PAGE_SIZE, "PDCR: %08x\nPTCR: %08x\n",
+ ret = scnprintf(buf, PAGE_SIZE, "PDCR: %08x\nPTCR: %08x\n",
pdcr, ptcr);
if (ptcr & IMX_AUDMUX_V2_PTCR_TFSDIR)
- ret += snprintf(buf + ret, PAGE_SIZE - ret,
+ ret += scnprintf(buf + ret, PAGE_SIZE - ret,
"TxFS output from %s, ",
audmux_port_string((ptcr >> 27) & 0x7));
else
- ret += snprintf(buf + ret, PAGE_SIZE - ret,
+ ret += scnprintf(buf + ret, PAGE_SIZE - ret,
"TxFS input, ");
if (ptcr & IMX_AUDMUX_V2_PTCR_TCLKDIR)
- ret += snprintf(buf + ret, PAGE_SIZE - ret,
+ ret += scnprintf(buf + ret, PAGE_SIZE - ret,
"TxClk output from %s",
audmux_port_string((ptcr >> 22) & 0x7));
else
- ret += snprintf(buf + ret, PAGE_SIZE - ret,
+ ret += scnprintf(buf + ret, PAGE_SIZE - ret,
"TxClk input");
- ret += snprintf(buf + ret, PAGE_SIZE - ret, "\n");
+ ret += scnprintf(buf + ret, PAGE_SIZE - ret, "\n");
if (ptcr & IMX_AUDMUX_V2_PTCR_SYN) {
- ret += snprintf(buf + ret, PAGE_SIZE - ret,
+ ret += scnprintf(buf + ret, PAGE_SIZE - ret,
"Port is symmetric");
} else {
if (ptcr & IMX_AUDMUX_V2_PTCR_RFSDIR)
- ret += snprintf(buf + ret, PAGE_SIZE - ret,
+ ret += scnprintf(buf + ret, PAGE_SIZE - ret,
"RxFS output from %s, ",
audmux_port_string((ptcr >> 17) & 0x7));
else
- ret += snprintf(buf + ret, PAGE_SIZE - ret,
+ ret += scnprintf(buf + ret, PAGE_SIZE - ret,
"RxFS input, ");
if (ptcr & IMX_AUDMUX_V2_PTCR_RCLKDIR)
- ret += snprintf(buf + ret, PAGE_SIZE - ret,
+ ret += scnprintf(buf + ret, PAGE_SIZE - ret,
"RxClk output from %s",
audmux_port_string((ptcr >> 12) & 0x7));
else
- ret += snprintf(buf + ret, PAGE_SIZE - ret,
+ ret += scnprintf(buf + ret, PAGE_SIZE - ret,
"RxClk input");
}
- ret += snprintf(buf + ret, PAGE_SIZE - ret,
+ ret += scnprintf(buf + ret, PAGE_SIZE - ret,
"\nData received from %s\n",
audmux_port_string((pdcr >> 13) & 0x7));