linux-kernel - Re: [PATCH 02/10] binfmt_elf: load interpreter program headers earlier

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Date:	Thu, 13 Nov 2014 18:29:29 +0100
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Paul Burton <paul.burton@...tec.com>, linux-mips@...ux-mips.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/10] binfmt_elf: load interpreter program headers
 earlier

On Thu, Nov 13, 2014 at 01:20:20PM +0100, Thierry Reding wrote:

> kmemleak started complaining for me recently and the stacktrace (see
> below) points to this function:
> 
> 	unreferenced object 0xec0f77c0 (size 192):
> 	  comm "kworker/u8:0", pid 169, jiffies 4294939367 (age 86.360s)
> 	  hex dump (first 32 bytes):
> 	    01 00 00 70 1c ef 01 00 1c ef 01 00 1c ef 01 00  ...p............
> 	    a0 00 00 00 a0 00 00 00 04 00 00 00 04 00 00 00  ................
> 	  backtrace:
> 	    [<c00ec080>] __kmalloc+0x104/0x190
> 	    [<c01387d4>] load_elf_phdrs+0x60/0x8c
> 	    [<c0138cb4>] load_elf_binary+0x280/0x12d8
> 	    [<c00f8ef0>] search_binary_handler+0x80/0x1f0
> 	    [<c00fa370>] do_execveat_common+0x570/0x658
> 	    [<c00fa480>] do_execve+0x28/0x30
> 	    [<c0038eb4>] ____call_usermodehelper+0x144/0x19c
> 	    [<c000e638>] ret_from_fork+0x14/0x3c
> 	    [<ffffffff>] 0xffffffff
[...]
> I think what happens is that the interp_elf_phdata memory is freed only
> in the error cleanup path, but not when the function actually succeeds.
> 
> The attached patch plugs the leak for me.
> 
> Thierry

> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index f95da60e440e..8a9be83e88c2 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -1029,6 +1029,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
>  		}
>  	}
>  
> +	kfree(interp_elf_phdata);
>  	kfree(elf_phdata);
>  
>  	set_binfmt(&elf_format);

Folded in and testing now.

  Ralf
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