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Message-ID: <d65340299e27ea3f187f05002c1d30d4c9fe8bf8.camel@kernel.org>
Date: Thu, 14 Nov 2024 09:51:42 -0500
From: Jeff Layton <jlayton@...nel.org>
To: Christian Brauner <brauner@...nel.org>, Miklos Szeredi
<miklos@...redi.hu>
Cc: Karel Zak <kzak@...hat.com>, Ian Kent <raven@...maw.net>, Josef Bacik
<josef@...icpanda.com>, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, Alexander Viro <viro@...iv.linux.org.uk>, Jan
Kara <jack@...e.cz>
Subject: Re: [PATCH v4 0/3] fs: allow statmount to fetch the fs_subtype and
sb_source
On Thu, 2024-11-14 at 15:48 +0100, Christian Brauner wrote:
> On Thu, Nov 14, 2024 at 02:16:05PM +0100, Miklos Szeredi wrote:
> > On Thu, 14 Nov 2024 at 13:29, Jeff Layton <jlayton@...nel.org> wrote:
> >
> > > Ordinarily, I might agree, but we're now growing a new mount option
> > > field that has them separated by NULs. Will we need two extra fields
> > > for this? One comma-separated, and one NUL separated?
> > >
> > > /proc/#/mountinfo and mounts prepend these to the output of
> > > ->show_options, so the simple solution would be to just prepend those
> > > there instead of adding a new field. FWIW, only SELinux has any extra
> > > mount options to show here.
> >
> > Compromise: tack them onto the end of the comma separated list, but
> > add a new field for the nul separated security options.
> >
> > I think this would be logical, since the comma separated list is more
> > useful for having a /proc/$$/mountinfo compatible string than for
> > actually interpreting what's in there.
>
> Fair. Here's an incremental for the array of security options.
>
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 4f39c4aba85d..a9065a9ab971 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -5072,13 +5072,30 @@ static int statmount_mnt_opts(struct kstatmount *s, struct seq_file *seq)
> return 0;
> }
>
> +static inline int statmount_opt_unescape(struct seq_file *seq, char *buf_start)
> +{
> + char *buf_end, *opt_start, *opt_end;
> + int count = 0;
> +
> + buf_end = seq->buf + seq->count;
> + *buf_end = '\0';
> + for (opt_start = buf_start + 1; opt_start < buf_end; opt_start = opt_end + 1) {
> + opt_end = strchrnul(opt_start, ',');
> + *opt_end = '\0';
> + buf_start += string_unescape(opt_start, buf_start, 0, UNESCAPE_OCTAL) + 1;
> + if (WARN_ON_ONCE(++count == INT_MAX))
> + return -EOVERFLOW;
> + }
> + seq->count = buf_start - 1 - seq->buf;
> + return count;
> +}
> +
> static int statmount_opt_array(struct kstatmount *s, struct seq_file *seq)
> {
> struct vfsmount *mnt = s->mnt;
> struct super_block *sb = mnt->mnt_sb;
> size_t start = seq->count;
> - char *buf_start, *buf_end, *opt_start, *opt_end;
> - u32 count = 0;
> + char *buf_start;
> int err;
>
> if (!sb->s_op->show_options)
> @@ -5095,17 +5112,39 @@ static int statmount_opt_array(struct kstatmount *s, struct seq_file *seq)
> if (seq->count == start)
> return 0;
>
> - buf_end = seq->buf + seq->count;
> - *buf_end = '\0';
> - for (opt_start = buf_start + 1; opt_start < buf_end; opt_start = opt_end + 1) {
> - opt_end = strchrnul(opt_start, ',');
> - *opt_end = '\0';
> - buf_start += string_unescape(opt_start, buf_start, 0, UNESCAPE_OCTAL) + 1;
> - if (WARN_ON_ONCE(++count == 0))
> - return -EOVERFLOW;
> - }
> - seq->count = buf_start - 1 - seq->buf;
> - s->sm.opt_num = count;
> + err = statmount_opt_unescape(seq, buf_start);
> + if (err < 0)
> + return err;
> +
> + s->sm.opt_num = err;
> + return 0;
> +}
> +
> +static int statmount_opt_sec_array(struct kstatmount *s, struct seq_file *seq)
> +{
> + struct vfsmount *mnt = s->mnt;
> + struct super_block *sb = mnt->mnt_sb;
> + size_t start = seq->count;
> + char *buf_start;
> + int err;
> +
> + buf_start = seq->buf + start;
> +
> + err = security_sb_show_options(seq, sb);
> + if (!err)
> + return err;
> +
> + if (unlikely(seq_has_overflowed(seq)))
> + return -EAGAIN;
> +
> + if (seq->count == start)
> + return 0;
> +
> + err = statmount_opt_unescape(seq, buf_start);
> + if (err < 0)
> + return err;
> +
> + s->sm.opt_sec_num = err;
> return 0;
> }
>
> @@ -5138,6 +5177,10 @@ static int statmount_string(struct kstatmount *s, u64 flag)
> sm->opt_array = start;
> ret = statmount_opt_array(s, seq);
> break;
> + case STATMOUNT_OPT_SEC_ARRAY:
> + sm->opt_sec_array = start;
> + ret = statmount_opt_sec_array(s, seq);
> + break;
> case STATMOUNT_FS_SUBTYPE:
> sm->fs_subtype = start;
> statmount_fs_subtype(s, seq);
> @@ -5294,6 +5337,9 @@ static int do_statmount(struct kstatmount *s, u64 mnt_id, u64 mnt_ns_id,
> if (!err && s->mask & STATMOUNT_OPT_ARRAY)
> err = statmount_string(s, STATMOUNT_OPT_ARRAY);
>
> + if (!err && s->mask & STATMOUNT_OPT_SEC_ARRAY)
> + err = statmount_string(s, STATMOUNT_OPT_SEC_ARRAY);
> +
> if (!err && s->mask & STATMOUNT_FS_SUBTYPE)
> err = statmount_string(s, STATMOUNT_FS_SUBTYPE);
>
> @@ -5323,7 +5369,7 @@ static inline bool retry_statmount(const long ret, size_t *seq_size)
> #define STATMOUNT_STRING_REQ (STATMOUNT_MNT_ROOT | STATMOUNT_MNT_POINT | \
> STATMOUNT_FS_TYPE | STATMOUNT_MNT_OPTS | \
> STATMOUNT_FS_SUBTYPE | STATMOUNT_SB_SOURCE | \
> - STATMOUNT_OPT_ARRAY)
> + STATMOUNT_OPT_ARRAY | STATMOUNT_OPT_SEC_ARRAY)
>
> static int prepare_kstatmount(struct kstatmount *ks, struct mnt_id_req *kreq,
> struct statmount __user *buf, size_t bufsize,
> diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h
> index c0fda4604187..569d938a5757 100644
> --- a/include/uapi/linux/mount.h
> +++ b/include/uapi/linux/mount.h
> @@ -177,7 +177,9 @@ struct statmount {
> __u32 sb_source; /* [str] Source string of the mount */
> __u32 opt_num; /* Number of fs options */
> __u32 opt_array; /* [str] Array of nul terminated fs options */
> - __u64 __spare2[47];
> + __u32 opt_sec_num; /* Number of security options */
> + __u32 opt_sec_array; /* [str] Array of nul terminated security options */
> + __u64 __spare2[45];
shouldn't that be 46 ?
> char str[]; /* Variable size part containing strings */
> };
>
> @@ -214,6 +216,7 @@ struct mnt_id_req {
> #define STATMOUNT_FS_SUBTYPE 0x00000100U /* Want/got fs_subtype */
> #define STATMOUNT_SB_SOURCE 0x00000200U /* Want/got sb_source */
> #define STATMOUNT_OPT_ARRAY 0x00000400U /* Want/got opt_... */
> +#define STATMOUNT_OPT_SEC_ARRAY 0x00000800U /* Want/got opt_sec... */
>
> /*
> * Special @mnt_id values that can be passed to listmount
The rest looks good to me though!
--
Jeff Layton <jlayton@...nel.org>
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