From 61423bef6335af90bd7f04d626a83d57df649c33 Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky Date: Thu, 14 Feb 2019 20:48:19 +0800 Subject: [PATCH] printk: fix integer overflow in setup_log_buf() mainline inclusion from mainline-4.20 commit d2130e82e945 category: bugfix bugzilla: 5761 CVE: NA ------------------------------------------------- The way we calculate logbuf free space percentage overflows signed integer: int free; free = __LOG_BUF_LEN - log_next_idx; pr_info("early log buf free: %u(%u%%)\n", free, (free * 100) / __LOG_BUF_LEN); We support LOG_BUF_LEN of up to 1<<25 bytes. Since setup_log_buf() is called during early init, logbuf is mostly empty, so __LOG_BUF_LEN - log_next_idx is close to 1<<25. Thus when we multiply it by 100, we overflow signed integer value range: 100 is 2^6 + 2^5 + 2^2. Example, booting with LOG_BUF_LEN 1<<25 and log_buf_len=2G boot param: [ 0.075317] log_buf_len: -2147483648 bytes [ 0.075319] early log buf free: 33549896(-28%) Make "free" unsigned integer and use appropriate printk() specifier. Link: http://lkml.kernel.org/r/20181010113308.9337-1-sergey.senozhatsky@gmail.com To: Steven Rostedt Cc: linux-kernel@vger.kernel.org Cc: Sergey Senozhatsky Signed-off-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Signed-off-by: Cheng Jian Reviewed-by: Xie XiuQi Signed-off-by: Yang Yingliang --- kernel/printk/printk.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index a0bd6fbeffb5..0061b4688da3 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1098,7 +1098,7 @@ void __init setup_log_buf(int early) { unsigned long flags; char *new_log_buf; - int free; + unsigned int free; if (log_buf != __log_buf) return; -- GitLab