linux-kernel - Re: [slabinfo PATCH] Fix off-by-one after readlink() call

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Date:	Fri, 14 Oct 2011 12:16:58 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	Thomas Jarosch <thomas.jarosch@...ra2net.com>
cc:	linux-kernel@...r.kernel.org, Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [slabinfo PATCH] Fix off-by-one after readlink() call

On Fri, 14 Oct 2011, Thomas Jarosch wrote:

> index 868cc93..cc1a378 100644
> --- a/tools/slub/slabinfo.c
> +++ b/tools/slub/slabinfo.c
> @@ -1145,7 +1145,7 @@ static void read_slab_dir(void)
>  		switch (de->d_type) {
>  		   case DT_LNK:
>  			alias->name = strdup(de->d_name);
> -			count = readlink(de->d_name, buffer, sizeof(buffer));
> +			count = readlink(de->d_name, buffer, sizeof(buffer)-1);
>

readlink required that the buffer size be specified.

READLINK(2)                                              Linux Programmer's Manual                                              READLINK(2)

NAME
       readlink - read value of a symbolic link

SYNOPSIS
       #include <unistd.h>

       ssize_t readlink(const char *path, char *buf, size_t bufsiz);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       readlink(): _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200112L

DESCRIPTION
       readlink()  places  the  contents  of the symbolic link path in the buffer buf, which has size bufsiz.  readlink() does not append a
       null byte to buf.  It will truncate the contents (to a length of bufsiz characters), in case the buffer is too small to hold all  of
       the contents.


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