Applied "spi: dw: change snprintf to scnprintf for possible overflow" to the spi tree

[Mark Brown <broonie@xxxxxxxxxx>]

The patch

   spi: dw: change snprintf to scnprintf for possible overflow

has been applied to the spi tree at

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From d1d6bd785da0c0c08523ee4f1a2d6a0875aa6f41 Mon Sep 17 00:00:00 2001
From: Silvio Cesare <silvio.cesare@xxxxxxxxx>
Date: Sat, 12 Jan 2019 16:28:44 +0100
Subject: [PATCH] spi: dw: change snprintf to scnprintf for possible overflow

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>
Signed-off-by: Willy Tarreau <w@xxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
---
 drivers/spi/spi-dw.c | 36 ++++++++++++++++++------------------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/drivers/spi/spi-dw.c b/drivers/spi/spi-dw.c
index 2e822a56576a..4c9deb434b3a 100644
--- a/drivers/spi/spi-dw.c
+++ b/drivers/spi/spi-dw.c
@@ -54,41 +54,41 @@ static ssize_t dw_spi_show_regs(struct file *file, char __user *user_buf,
 	if (!buf)
 		return 0;
 
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"%s registers:\n", dev_name(&dws->master->dev));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"=================================\n");
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"CTRL0: \t\t0x%08x\n", dw_readl(dws, DW_SPI_CTRL0));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"CTRL1: \t\t0x%08x\n", dw_readl(dws, DW_SPI_CTRL1));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"SSIENR: \t0x%08x\n", dw_readl(dws, DW_SPI_SSIENR));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"SER: \t\t0x%08x\n", dw_readl(dws, DW_SPI_SER));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"BAUDR: \t\t0x%08x\n", dw_readl(dws, DW_SPI_BAUDR));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"TXFTLR: \t0x%08x\n", dw_readl(dws, DW_SPI_TXFLTR));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"RXFTLR: \t0x%08x\n", dw_readl(dws, DW_SPI_RXFLTR));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"TXFLR: \t\t0x%08x\n", dw_readl(dws, DW_SPI_TXFLR));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"RXFLR: \t\t0x%08x\n", dw_readl(dws, DW_SPI_RXFLR));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"SR: \t\t0x%08x\n", dw_readl(dws, DW_SPI_SR));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"IMR: \t\t0x%08x\n", dw_readl(dws, DW_SPI_IMR));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"ISR: \t\t0x%08x\n", dw_readl(dws, DW_SPI_ISR));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"DMACR: \t\t0x%08x\n", dw_readl(dws, DW_SPI_DMACR));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"DMATDLR: \t0x%08x\n", dw_readl(dws, DW_SPI_DMATDLR));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"DMARDLR: \t0x%08x\n", dw_readl(dws, DW_SPI_DMARDLR));
-	len += snprintf(buf + len, SPI_REGS_BUFSIZE - len,
+	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"=================================\n");
 
 	ret = simple_read_from_buffer(user_buf, count, ppos, buf, len);
-- 
2.20.1