From d1d6bd785da0c0c08523ee4f1a2d6a0875aa6f41 Mon Sep 17 00:00:00 2001 From: Silvio Cesare 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 Signed-off-by: Willy Tarreau Reviewed-by: Kees Cook Signed-off-by: Mark Brown --- 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); -- 2.11.0