Re: [PATCH v2 3/4] linux/fs.h: fix umask on NFS with CONFIG_FS_POSIX_ACL=n

From: Jan Kara
Date: Tue Aug 27 2019 - 11:03:09 EST


On Sat 13-07-19 06:11:59, Max Kellermann wrote:
> Make IS_POSIXACL() return false if POSIX ACL support is disabled and
> 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
> 2. again (unconditionally) in nfs3_proc_mkdir()
> The first one does not apply, because even without
> 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
> Signed-off-by: Max Kellermann <mk@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx

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

Reviewed-by: Jan Kara <jack@xxxxxxx>

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@xxxxxxxxxxxxxxxxxx> - to CC to merge the patch.


> ---
> 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)
> +
> #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@xxxxxxxx>