[PATCH] ath9k/eeprom: Use scnprintf instead of snprintf

[PATCH] ath9k/eeprom: Use scnprintf instead of snprintf

[Kees Cook]

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.

Cc: Willy Tarreau <w@1wt.eu>
Cc: Silvio Cesare <silvio.cesare@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/net/wireless/ath/ath9k/ar9003_eeprom.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/net/wireless/ath/ath9k/ar9003_eeprom.c b/drivers/net/wireless/ath/ath9k/ar9003_eeprom.c
index f019a20e5a1f..2b29bf4730f6 100644
--- a/drivers/net/wireless/ath/ath9k/ar9003_eeprom.c
+++ b/drivers/net/wireless/ath/ath9k/ar9003_eeprom.c
@@ -3457,9 +3457,9 @@ static u32 ar9003_dump_cal_data(struct ath_hw *ah, char *buf, u32 len, u32 size,
 		if (!((pBase->txrxMask >> i) & 1))
 			continue;
 
-		len += snprintf(buf + len, size - len, "Chain %d\n", i);
+		len += scnprintf(buf + len, size - len, "Chain %d\n", i);
 
-		len += snprintf(buf + len, size - len,
+		len += scnprintf(buf + len, size - len,
 			"Freq\t ref\tvolt\ttemp\tnf_cal\tnf_pow\trx_temp\n");
 
 		for (j = 0; j < cal_pier_nr; j++) {
@@ -3471,10 +3471,10 @@ static u32 ar9003_dump_cal_data(struct ath_hw *ah, char *buf, u32 len, u32 size,
 				freq = 4800 + eep->calFreqPier5G[j] * 5;
 			}
 
-			len += snprintf(buf + len, size - len,
+			len += scnprintf(buf + len, size - len,
 				"%d\t", freq);
 
-			len += snprintf(buf + len, size - len,
+			len += scnprintf(buf + len, size - len,
 				"%d\t%d\t%d\t%d\t%d\t%d\n",
 				cal_pier->refPower,
 				cal_pier->voltMeas,
@@ -3505,12 +3505,12 @@ static u32 ath9k_hw_ar9003_dump_eeprom(struct ath_hw *ah, bool dump_base_hdr,
 		len += scnprintf(buf + len, size - len, "Calibration data\n");
 		len = ar9003_dump_cal_data(ah, buf, len, size, true);
 
-		len +=  snprintf(buf + len, size - len,
+		len += scnprintf(buf + len, size - len,
 				 "%20s :\n", "5GHz modal Header");
 		len = ar9003_dump_modal_eeprom(buf, len, size,
 						&eep->modalHeader5G);
 
-		len += snprintf(buf + len, size - len, "Calibration data\n");
+		len += scnprintf(buf + len, size - len, "Calibration data\n");
 		len = ar9003_dump_cal_data(ah, buf, len, size, false);
 
 		goto out;
-- 
2.17.1


-- 
Kees Cook

Re: [PATCH] ath9k/eeprom: Use scnprintf instead of snprintf

[Kalle Valo]

Kees Cook <keescook@chromium.org> wrote:

> 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.
> 
> Cc: Willy Tarreau <w@1wt.eu>
> Cc: Silvio Cesare <silvio.cesare@gmail.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

Patch applied to ath-next branch of ath.git, thanks.

4b6e9f3fe1d8 ath9k: eeprom: Use scnprintf instead of snprintf

-- 
https://patchwork.kernel.org/patch/10765259/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches