linux-kernel - Re: [PATCH] shm: Remove silly double assignment

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20080611034506.05ad07ae.akpm@linux-foundation.org>
Date:	Wed, 11 Jun 2008 03:45:06 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Neil Horman <nhorman@...driver.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH] shm: Remove silly double assignment

On Tue, 10 Jun 2008 08:53:39 -0400 Neil Horman <nhorman@...driver.com> wrote:

>     Found a silly double assignment of err is do_shmat.  Silly, but good to clean up
>     the useless code.
>     
>     Signed-off-by: Neil Horman <nhorman@...driver.com>
> 
> diff --git a/ipc/shm.c b/ipc/shm.c
> index 554429a..d05f6b5 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -894,8 +894,6 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
>  	if (!sfd)
>  		goto out_put_dentry;
>  
> -	err = -ENOMEM;
> -
>  	file = alloc_file(path.mnt, path.dentry, f_mode, &shm_file_operations);
>  	if (!file)
>  		goto out_free;

Not silly, really.  Look:

	err = -ENOMEM;
	if (expr1)
		goto out;

	err = -ENOMEM;
	if (expr2)
		goto out;

each of these two units is a separate, self-contained clause.  Removing
the second assignment to `err' breaks that separation and will make one
clause undesirably dependent upon the other.

Example: if someone later comes up and does

	err = -ENOMEM;
	if (expr1)
		goto out;

+	er = -EINVAL;
+	if (expr3)
+		goto out;

	if (expr2)
		goto out;

then whoops, it broke.

The compiler should optimise away the second assignment anyway.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/