linux/kernel/printk
Sergey Senozhatsky d2130e82e9 printk: fix integer overflow in setup_log_buf()
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 <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
2018-10-12 10:44:17 +02:00
..
Makefile printk: introduce per-cpu safe_print seq buffer 2017-02-08 11:07:11 +01:00
braille.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
braille.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
console_cmdline.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
internal.h printk/nmi: Prevent deadlock when accessing the main log buffer in NMI 2018-07-09 14:10:40 +02:00
printk.c printk: fix integer overflow in setup_log_buf() 2018-10-12 10:44:17 +02:00
printk_safe.c printk/tracing: Do not trace printk_nmi_enter() 2018-09-06 11:24:05 -04:00