From 4b23140193c5063438f6c5f1c0ba43f981609bb5 Mon Sep 17 00:00:00 2001
From: Lianbo Jiang <lijiang@redhat.com>
Date: Mon, 9 Sep 2019 09:48:10 +0800
Subject: [PATCH] Limit the size of vmcore-dmesg.txt to 2G

With some corrupted vmcore files, the vmcore-dmesg.txt file may grow
forever till the kdump disk becomes full, and also probably causes
the disk error messages as follow:
...
sd 0:0:0:0: [sda] tag#6 FAILED Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
sd 0:0:0:0: [sda] tag#6 CDB: Read(10) 28 00 08 06 4c 98 00 00 08 00
blk_update_request: I/O error, dev sda, sector 134630552
sd 0:0:0:0: [sda] tag#7 FAILED Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
sd 0:0:0:0: [sda] tag#7 CDB: Read(10) 28 00 08 06 4c 98 00 00 08 00
blk_update_request: I/O error, dev sda, sector 134630552
...

If vmcore-dmesg.txt occupies the whole disk, the vmcore can not be
saved, this is also a problem.

Lets limit the size of vmcore-dmesg.txt to avoid such problems.

Signed-off-by: Lianbo Jiang <lijiang@redhat.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
---
 vmcore-dmesg/vmcore-dmesg.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/vmcore-dmesg/vmcore-dmesg.c b/vmcore-dmesg/vmcore-dmesg.c
index a8f56dfbe51f..41ab73147155 100644
--- a/vmcore-dmesg/vmcore-dmesg.c
+++ b/vmcore-dmesg/vmcore-dmesg.c
@@ -22,6 +22,9 @@
 /* The 32bit and 64bit note headers make it clear we don't care */
 typedef Elf32_Nhdr Elf_Nhdr;
 
+/* stole this macro from kernel printk.c */
+#define LOG_BUF_LEN_MAX (uint32_t)(1 << 31)
+
 static const char *fname;
 static Elf64_Ehdr ehdr;
 static Elf64_Phdr *phdr;
@@ -476,6 +479,13 @@ static int32_t read_file_s32(int fd, uint64_t addr)
 static void write_to_stdout(char *buf, unsigned int nr)
 {
 	ssize_t ret;
+	static uint32_t n_bytes = 0;
+
+	n_bytes += nr;
+	if (n_bytes > LOG_BUF_LEN_MAX) {
+		fprintf(stderr, "The vmcore-dmesg.txt over 2G in size is not supported.\n");
+		exit(53);
+	}
 
 	ret = write(STDOUT_FILENO, buf, nr);
 	if (ret != nr) {
-- 
2.17.1