linux-ext4 - Re: [PATCH 2/2] ext4: don't fail GETFSUUID when the caller provides a long buffer

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Date:   Fri, 11 Nov 2022 01:13:17 +0000
From:   Catherine Hoang <catherine.hoang@...cle.com>
To:     "Darrick J. Wong" <djwong@...nel.org>
CC:     "tytso@....edu" <tytso@....edu>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 2/2] ext4: don't fail GETFSUUID when the caller provides a
 long buffer

> On Nov 10, 2022, at 12:16 PM, Darrick J. Wong <djwong@...nel.org> wrote:
> 
> From: Darrick J. Wong <djwong@...nel.org>
> 
> If userspace provides a longer UUID buffer than is required, we
> shouldn't fail the call with EINVAL -- rather, we can fill the caller's
> buffer with the bytes we /can/ fill, and update the length field to
> reflect what we copied.  This doesn't break the UAPI since we're
> enabling a case that currently fails, and so far Ted hasn't released a
> version of e2fsprogs that uses the new ext4 ioctl.
> 
> Signed-off-by: Darrick J. Wong <djwong@...nel.org>

Looks good
Reviewed-by: Catherine Hoang <catherine.hoang@...cle.com>
> ---
> fs/ext4/ioctl.c |    6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
> 
> 
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index 5f91f3ad3e50..31e643795016 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -1159,14 +1159,16 @@ static int ext4_ioctl_getuuid(struct ext4_sb_info *sbi,
> 		return 0;
> 	}
> 
> -	if (fsuuid.fsu_len != UUID_SIZE || fsuuid.fsu_flags != 0)
> +	if (fsuuid.fsu_len < UUID_SIZE || fsuuid.fsu_flags != 0)
> 		return -EINVAL;
> 
> 	lock_buffer(sbi->s_sbh);
> 	memcpy(uuid, sbi->s_es->s_uuid, UUID_SIZE);
> 	unlock_buffer(sbi->s_sbh);
> 
> -	if (copy_to_user(&ufsuuid->fsu_uuid[0], uuid, UUID_SIZE))
> +	fsuuid.fsu_len = UUID_SIZE;
> +	if (copy_to_user(ufsuuid, &fsuuid, sizeof(fsuuid)) ||
> +	    copy_to_user(&ufsuuid->fsu_uuid[0], uuid, UUID_SIZE))
> 		return -EFAULT;
> 	return 0;
> }
>