linux-kernel - Re: [PATCH] binfmt_elf.c : the BAD

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Message-ID: <20060822043642.GB9489@1wt.eu>
Date:	Tue, 22 Aug 2006 06:36:43 +0200
From:	Willy Tarreau <w@....eu>
To:	Ernie Petrides <petrides@...hat.com>
Cc:	Marcelo Tosatti <marcelo@...ck.org>,
	Solar Designer <solar@...nwall.com>,
	Chuck Ebbert <76306.1226@...puserve.com>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] binfmt_elf.c : the BAD_ADDR macro again

On Mon, Aug 21, 2006 at 07:36:01PM -0400, Ernie Petrides wrote:
> On Monday, 21-Aug-2006 at 23:11 +0200, Willy Tarreau wrote:
> 
> > > > [...]   But before this, I'd like to get comments from
> > > > the people who discussed the subject recently.
> > >
> > > Thus, I think that both 2.4.33 and 2.6.<latest> are okay without any
> > > further changes.
> >
> > At least 2.4 needs the fix to use the correct BAD_ADDR (which is not
> > OK in 2.4.33 yet).
> 
> Ah, right.  (Sorry, I was verifying the change in a RHEL3 tree.)
> 
> In that case, I support your patch as posted.  But the whole point of
> that investigation was to fix an exec() vulnerability with a bad ELF
> entry address.  This is addressed in the final hunk of the 2.4.33-based
> patch below, which includes the changes that you previously posted.
> 
> Cheers.  -ernie

Thanks Ernie.
However, I will just comment the printk out instead of removing it
for now. I've backported the prink_ratelimit() function from 2.6,
but I've not tested it yet. My goal is to use it there (and at other
places where messages can be triggered at will by a user).

About Solar Designer's concern about the string passed to printk, I'm
wondering if it would not be printk() itself which should strip
non printable chars. It would seem very strange to me that any part
of the kernel needs to send \n or \e via strings sent to printk. Well,
after having seen ugly code in some drivers, anything can be expected,
but we could try anyway.

It would be another patch anyway

Cheers,
Willy

> Signed-off-by: Ernie Petrides <petrides@...hat.com>
> 
> --- linux-2.4.33/fs/binfmt_elf.c.orig
> +++ linux-2.4.33/fs/binfmt_elf.c
> @@ -77,7 +77,7 @@ static struct linux_binfmt elf_format = 
>  	NULL, THIS_MODULE, load_elf_binary, load_elf_library, elf_core_dump, ELF_EXEC_PAGESIZE
>  };
>  
> -#define BAD_ADDR(x)	((unsigned long)(x) > TASK_SIZE)
> +#define BAD_ADDR(x)	((unsigned long)(x) >= TASK_SIZE)
>  
>  static int set_brk(unsigned long start, unsigned long end)
>  {
> @@ -345,7 +345,7 @@ elf_type, total_size);
>  	     * <= p_memsize so it is only necessary to check p_memsz.
>  	     */
>  	    k = load_addr + eppnt->p_vaddr;
> -	    if (k > TASK_SIZE || eppnt->p_filesz > eppnt->p_memsz ||
> +	    if (BAD_ADDR(k) || eppnt->p_filesz > eppnt->p_memsz ||
>  		eppnt->p_memsz > TASK_SIZE || TASK_SIZE - eppnt->p_memsz < k) {
>  	        error = -ENOMEM;
>  		goto out_close;
> @@ -772,7 +772,7 @@ static int load_elf_binary(struct linux_
>  		 * allowed task size. Note that p_filesz must always be
>  		 * <= p_memsz so it is only necessary to check p_memsz.
>  		 */
> -		if (k > TASK_SIZE || elf_ppnt->p_filesz > elf_ppnt->p_memsz ||
> +		if (BAD_ADDR(k) || elf_ppnt->p_filesz > elf_ppnt->p_memsz ||
>  		    elf_ppnt->p_memsz > TASK_SIZE ||
>  		    TASK_SIZE - elf_ppnt->p_memsz < k) {
>  			/* set_brk can never work.  Avoid overflows.  */
> @@ -822,10 +822,9 @@ static int load_elf_binary(struct linux_
>  						    interpreter,
>  						    &interp_load_addr);
>  		if (BAD_ADDR(elf_entry)) {
> -			printk(KERN_ERR "Unable to load interpreter %.128s\n",
> -				elf_interpreter);
>  			force_sig(SIGSEGV, current);
> -			retval = IS_ERR((void *)elf_entry) ? PTR_ERR((void *)elf_entry) : -ENOEXEC;
> +			retval = IS_ERR((void *)elf_entry) ?
> +					(int)elf_entry : -EINVAL;
>  			goto out_free_dentry;
>  		}
>  		reloc_func_desc = interp_load_addr;
> @@ -833,6 +832,12 @@ static int load_elf_binary(struct linux_
>  		allow_write_access(interpreter);
>  		fput(interpreter);
>  		kfree(elf_interpreter);
> +	} else {
> +		if (BAD_ADDR(elf_entry)) {
> +			force_sig(SIGSEGV, current);
> +			retval = -EINVAL;
> +			goto out_free_dentry;
> +		}
>  	}
>  
>  	kfree(elf_phdata);
-
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