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Date: Wed, 10 Oct 2018 20:33:08 +0900
From: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>,
Petr Mladek <pmladek@...e.com>
Cc: linux-kernel@...r.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: [PATCH] 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.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
---
kernel/printk/printk.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index c3f0e3927e77..c9e1d3bf695e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1083,7 +1083,7 @@ 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;
@@ -1116,8 +1116,8 @@ void __init setup_log_buf(int early)
memcpy(log_buf, __log_buf, __LOG_BUF_LEN);
logbuf_unlock_irqrestore(flags);
- pr_info("log_buf_len: %d bytes\n", log_buf_len);
- pr_info("early log buf free: %d(%d%%)\n",
+ pr_info("log_buf_len: %u bytes\n", log_buf_len);
+ pr_info("early log buf free: %u(%u%%)\n",
free, (free * 100) / __LOG_BUF_LEN);
}
--
2.19.1
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