From 87bf65bc108e5da18e7ec788e9a4fb96263f19b7 Mon Sep 17 00:00:00 2001 From: Silvio Cesare Date: Sat, 12 Jan 2019 16:28:37 +0100 Subject: [PATCH] lkdtm: 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 Cc: Dan Carpenter Cc: Will Deacon Cc: Greg KH Acked-by: Kees Cook Signed-off-by: Willy Tarreau Signed-off-by: Greg Kroah-Hartman --- drivers/misc/lkdtm/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c index c09133ac9803..b51cf182b031 100644 --- a/drivers/misc/lkdtm/core.c +++ b/drivers/misc/lkdtm/core.c @@ -340,9 +340,9 @@ static ssize_t lkdtm_debugfs_read(struct file *f, char __user *user_buf, if (buf == NULL) return -ENOMEM; - n = snprintf(buf, PAGE_SIZE, "Available crash types:\n"); + n = scnprintf(buf, PAGE_SIZE, "Available crash types:\n"); for (i = 0; i < ARRAY_SIZE(crashtypes); i++) { - n += snprintf(buf + n, PAGE_SIZE - n, "%s\n", + n += scnprintf(buf + n, PAGE_SIZE - n, "%s\n", crashtypes[i].name); } buf[n] = '\0'; -- 2.30.2