linux-kernel - Re: [PATCH v2 3/4] linux/fs.h: fix umask on NFS with CONFIG_FS_POSIX

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Date:   Tue, 27 Aug 2019 17:03:04 +0200
From:   Jan Kara <jack@...e.cz>
To:     Max Kellermann <mk@...all.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
        trond.myklebust@...merspace.com, bfields@...hat.com, tytso@....edu,
        adilger.kernel@...ger.ca, hughd@...gle.com,
        anna.schumaker@...app.com, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 3/4] linux/fs.h: fix umask on NFS with
 CONFIG_FS_POSIX_ACL=n

Hello,

On Sat 13-07-19 06:11:59, Max Kellermann wrote:
> Make IS_POSIXACL() return false if POSIX ACL support is disabled and
> ignore SB_POSIXACL/MS_POSIXACL.
> 
> Never skip applying the umask in namei.c and never bother to do any
> ACL specific checks if the filesystem falsely indicates it has ACLs
> enabled when the feature is completely disabled in the kernel.
> 
> This fixes a problem where the umask is always ignored in the NFS
> client when compiled without CONFIG_FS_POSIX_ACL.  This is a 4 year
> old regression caused by commit 013cdf1088d723 which itself was not
> completely wrong, but failed to consider all the side effects by
> misdesigned VFS code.
> 
> Prior to that commit, there were two places where the umask could be
> applied, for example when creating a directory:
> 
>  1. in the VFS layer in SYSCALL_DEFINE3(mkdirat), but only if
>     !IS_POSIXACL()
> 
>  2. again (unconditionally) in nfs3_proc_mkdir()
> 
> The first one does not apply, because even without
> CONFIG_FS_POSIX_ACL, the NFS client sets MS_POSIXACL in
> nfs_fill_super().
> 
> After that commit, (2.) was replaced by:
> 
>  2b. in posix_acl_create(), called by nfs3_proc_mkdir()
> 
> There's one branch in posix_acl_create() which applies the umask;
> however, without CONFIG_FS_POSIX_ACL, posix_acl_create() is an empty
> dummy function which does not apply the umask.
> 
> The approach chosen by this patch is to make IS_POSIXACL() always
> return false when POSIX ACL support is disabled, so the umask always
> gets applied by the VFS layer.  This is consistent with the (regular)
> behavior of posix_acl_create(): that function returns early if
> IS_POSIXACL() is false, before applying the umask.
> 
> Therefore, posix_acl_create() is responsible for applying the umask if
> there is ACL support enabled in the file system (SB_POSIXACL), and the
> VFS layer is responsible for all other cases (no SB_POSIXACL or no
> CONFIG_FS_POSIX_ACL).
> 
> Signed-off-by: Max Kellermann <mk@...all.com>
> Cc: stable@...r.kernel.org

Thanks for the patch. This patch definitely looks good to me so feel free
to add:

Reviewed-by: Jan Kara <jack@...e.cz>

I just wonder, do you really need patches 1 and 2? Doesn't this patch alone
fix the problem? Because AFAIU the problem, this patch should be enough and
indeed the logic "VFS is responsible for applying umask if !IS_POSIXACL and
otherwise posix_acl_create() is responsible for it" looks the most logical
to me. BTW, I think you should add VFS maintainer - Al Viro
<viro@...IV.linux.org.uk> - to CC to merge the patch.

								Honza

> ---
>  include/linux/fs.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index f7fdfe93e25d..5e9f3aa7ba26 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1993,7 +1993,12 @@ static inline bool sb_rdonly(const struct super_block *sb) { return sb->s_flags
>  #define IS_NOQUOTA(inode)	((inode)->i_flags & S_NOQUOTA)
>  #define IS_APPEND(inode)	((inode)->i_flags & S_APPEND)
>  #define IS_IMMUTABLE(inode)	((inode)->i_flags & S_IMMUTABLE)
> +
> +#ifdef CONFIG_FS_POSIX_ACL
>  #define IS_POSIXACL(inode)	__IS_FLG(inode, SB_POSIXACL)
> +#else
> +#define IS_POSIXACL(inode)	0
> +#endif
>  
>  #define IS_DEADDIR(inode)	((inode)->i_flags & S_DEAD)
>  #define IS_NOCMTIME(inode)	((inode)->i_flags & S_NOCMTIME)
> -- 
> 2.20.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR