[PATCH] vmcore-dmesg: Do not write beyond end of allocated buffer

[Simon Horman]

On Tue, Jul 17, 2012 at 11:23:00AM -0400, Vivek Goyal wrote:
> scan_vmcoreinfo() currently assumes that every line in vmcoreinfo note ends
> with \n and overwrites new line character with \0. But last entry in note,
> CRASHTIME= does not end with \n and this leads to corrupting memory as we
> write beyond end of buffer.
> 
> Normally things were fine but when I added some fields to vmcoreinfo, this
> bug started showing and vmcore-dmesg started crashing.
> 
> I am planning to send a patch to fix this in kernel but it might be good
> idea to handle this case in user space too so that vmcore-dmesg works
> fine with cores of older kernels.

Good plan.

> Signed-off-by: Vivek Goyal <vgoyal at redhat.com>
> ---
>  vmcore-dmesg/vmcore-dmesg.c |   27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
> 
> Index: kexec-tools/vmcore-dmesg/vmcore-dmesg.c
> ===================================================================
> --- kexec-tools.orig/vmcore-dmesg/vmcore-dmesg.c	2012-07-19 01:54:02.700700235 -0400
> +++ kexec-tools/vmcore-dmesg/vmcore-dmesg.c	2012-07-19 01:55:08.232702248 -0400
> @@ -14,6 +14,7 @@
>  #include <sys/stat.h>
>  #include <fcntl.h>
>  #include <elf.h>
> +#include <stdbool.h>
>  
>  /* The 32bit and 64bit note headers make it clear we don't care */
>  typedef Elf32_Nhdr Elf_Nhdr;
> @@ -220,6 +221,9 @@ static void scan_vmcoreinfo(char *start,
>  {
>  	char *last = start + size - 1;
>  	char *pos, *eol;
> +	char temp_buf[1024];
> +	bool last_line = false;

Is there a chance of over-running temp_buf?

I would be more comfortable if there was a check below to
ensure that len can never be greater than sizeof(temp_buf).

> +
>  #define SYMBOL(sym) {					\
>  	.str = "SYMBOL(" #sym  ")=",			\
>  	.name = #sym,					\
> @@ -243,7 +247,25 @@ static void scan_vmcoreinfo(char *start,
>  		/* Find the end of the current line */
>  		for (eol = pos; (eol <= last) && (*eol != '\n') ; eol++)
>  			;
> -		len = eol - pos + 1;
> +		if (eol > last) {
> +			/*
> +			 * We did not find \n and note ended. Currently kernel
> +			 * is appending last field CRASH_TIME without \n. It
> +			 * is ugly but handle it.
> +			 */
> +			eol = last;
> +			len = eol - pos + 1;
> +			strncpy(temp_buf, pos, len);
> +			temp_buf[len + 1] = '\0';
> +
> +			pos = temp_buf;
> +			len = len + 1;
> +			eol = pos + len -1;
> +			last_line = true;
> +		} else  {
> +			len = eol - pos + 1;
> +		}
> +
>  		/* Stomp the last character so I am guaranteed a terminating null */
>  		*eol = '\0';
>  		/* Copy OSRELEASE if I see it */
> @@ -266,6 +288,9 @@ static void scan_vmcoreinfo(char *start,
>  			/* Remember the virtual address */
>  			*symbol[i].vaddr = vaddr;
>  		}
> +
> +		if (last_line)
> +			break;
>  	}
>  }
>  
>