linux-kernel - Re: [PATCH next] binfmt_elf: Fix potential Oops in load_elf

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Message-ID: <20241211164821.ki4wy4ltffgx677t@quack3>
Date: Wed, 11 Dec 2024 17:48:21 +0100
From: Jan Kara <jack@...e.cz>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Amir Goldstein <amir73il@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	Kees Cook <kees@...nel.org>, Eric Biederman <ebiederm@...ssion.com>,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH next] binfmt_elf: Fix potential Oops in load_elf_binary()

On Wed 11-12-24 12:21:39, Dan Carpenter wrote:
> This function call was changed from allow_write_access() which has a NULL
> check to exe_file_allow_write_access() which doesn't.  Check for NULL
> before calling it.
> 
> Fixes: 871387b27c20 ("fs: don't block write during exec on pre-content watched files")
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>

Thanks for noticing! I've opted to change exe_file_allow_write_access() to
check for NULL instead to be 1:1 replacement for allow_write_access().
Because bugs like this one are very easy to introduce.

								Honza

> ---
>  fs/binfmt_elf.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 8054f44d39cf..db9cb4c20125 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -1354,9 +1354,10 @@ static int load_elf_binary(struct linux_binprm *bprm)
>  	kfree(interp_elf_ex);
>  	kfree(interp_elf_phdata);
>  out_free_file:
> -	exe_file_allow_write_access(interpreter);
> -	if (interpreter)
> +	if (interpreter) {
> +		exe_file_allow_write_access(interpreter);
>  		fput(interpreter);
> +	}
>  out_free_ph:
>  	kfree(elf_phdata);
>  	goto out;
> -- 
> 2.45.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR