linux-kernel - Re: [PATCH] libfs: fix accidental overflow in offset calculation

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Message-ID: <20240510004906.GU2118490@ZenIV>
Date: Fri, 10 May 2024 01:49:06 +0100
From: Al Viro <viro@...iv.linux.org.uk>
To: Justin Stitt <justinstitt@...gle.com>
Cc: Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	Nathan Chancellor <nathan@...nel.org>,
	Bill Wendling <morbo@...gle.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] libfs: fix accidental overflow in offset calculation

On Fri, May 10, 2024 at 12:35:51AM +0000, Justin Stitt wrote:
> @@ -147,7 +147,9 @@ loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
>  	struct dentry *dentry = file->f_path.dentry;
>  	switch (whence) {
>  		case 1:
> -			offset += file->f_pos;
> +			/* cannot represent offset with loff_t */
> +			if (check_add_overflow(offset, file->f_pos, &offset))
> +				return -EOVERFLOW;

Instead of -EINVAL it correctly returns in such cases?  Why?