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    SubjectRe: [patch 07/10] unprivileged mounts: add sysctl tunable for "safe" property
    Quoting Miklos Szeredi (miklos@szeredi.hu):
    > From: Miklos Szeredi <mszeredi@suse.cz>
    >
    > Add the following:
    >
    > /proc/sys/fs/types/${FS_TYPE}/usermount_safe
    >
    > Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
    > ---
    >
    > Index: linux/fs/filesystems.c
    > ===================================================================
    > --- linux.orig/fs/filesystems.c 2008-01-16 13:24:52.000000000 +0100
    > +++ linux/fs/filesystems.c 2008-01-16 13:25:09.000000000 +0100
    > @@ -12,6 +12,7 @@
    > #include <linux/kmod.h>
    > #include <linux/init.h>
    > #include <linux/module.h>
    > +#include <linux/sysctl.h>
    > #include <asm/uaccess.h>
    >
    > /*
    > @@ -51,6 +52,57 @@ static struct file_system_type **find_fi
    > return p;
    > }
    >
    > +#define MAX_FILESYSTEM_VARS 1
    > +
    > +struct filesystem_sysctl_table {
    > + struct ctl_table_header *header;
    > + struct ctl_table table[MAX_FILESYSTEM_VARS + 1];
    > +};
    > +
    > +/*
    > + * Create /sys/fs/types/${FSNAME} directory with per fs-type tunables.
    > + */
    > +static int filesystem_sysctl_register(struct file_system_type *fs)
    > +{
    > + struct filesystem_sysctl_table *t;
    > + struct ctl_path path[] = {
    > + { .procname = "fs", .ctl_name = CTL_FS },
    > + { .procname = "types", .ctl_name = CTL_UNNUMBERED },
    > + { .procname = fs->name, .ctl_name = CTL_UNNUMBERED },
    > + { }
    > + };
    > +
    > + t = kzalloc(sizeof(*t), GFP_KERNEL);
    > + if (!t)
    > + return -ENOMEM;
    > +
    > +
    > + t->table[0].ctl_name = CTL_UNNUMBERED;
    > + t->table[0].procname = "usermount_safe";
    > + t->table[0].maxlen = sizeof(int);
    > + t->table[0].data = &fs->fs_safe;
    > + t->table[0].mode = 0644;
    > + t->table[0].proc_handler = &proc_dointvec;
    > +
    > + t->header = register_sysctl_paths(path, t->table);
    > + if (!t->header) {
    > + kfree(t);
    > + return -ENOMEM;
    > + }
    > +
    > + fs->sysctl_table = t;
    > +
    > + return 0;
    > +}
    > +
    > +static void filesystem_sysctl_unregister(struct file_system_type *fs)
    > +{
    > + struct filesystem_sysctl_table *t = fs->sysctl_table;
    > +
    > + unregister_sysctl_table(t->header);
    > + kfree(t);
    > +}
    > +
    > /**
    > * register_filesystem - register a new filesystem
    > * @fs: the file system structure
    > @@ -80,6 +132,13 @@ int register_filesystem(struct file_syst
    > else
    > *p = fs;
    > write_unlock(&file_systems_lock);
    > +
    > + if (res == 0) {
    > + res = filesystem_sysctl_register(fs);

    What do you think about doing this only if FS_SAFE is also set,
    so for instance at first only FUSE would allow itself to be
    made user-mountable?

    A safe thing to do, or overly intrusive?

    > + if (res != 0)
    > + unregister_filesystem(fs);
    > + }
    > +
    > return res;
    > }
    >
    > @@ -108,6 +167,7 @@ int unregister_filesystem(struct file_sy
    > *tmp = fs->next;
    > fs->next = NULL;
    > write_unlock(&file_systems_lock);
    > + filesystem_sysctl_unregister(fs);
    > return 0;
    > }
    > tmp = &(*tmp)->next;
    > Index: linux/include/linux/fs.h
    > ===================================================================
    > --- linux.orig/include/linux/fs.h 2008-01-16 13:25:09.000000000 +0100
    > +++ linux/include/linux/fs.h 2008-01-16 13:25:09.000000000 +0100
    > @@ -1437,6 +1437,7 @@ struct file_system_type {
    > struct module *owner;
    > struct file_system_type * next;
    > struct list_head fs_supers;
    > + struct filesystem_sysctl_table *sysctl_table;
    >
    > struct lock_class_key s_lock_key;
    > struct lock_class_key s_umount_key;
    > Index: linux/Documentation/filesystems/proc.txt
    > ===================================================================
    > --- linux.orig/Documentation/filesystems/proc.txt 2008-01-16 13:25:07.000000000 +0100
    > +++ linux/Documentation/filesystems/proc.txt 2008-01-16 13:25:09.000000000 +0100
    > @@ -43,6 +43,7 @@ Table of Contents
    > 2.13 /proc/<pid>/oom_score - Display current oom-killer score
    > 2.14 /proc/<pid>/io - Display the IO accounting fields
    > 2.15 /proc/<pid>/coredump_filter - Core dump filtering settings
    > + 2.16 /proc/sys/fs/types - File system type specific parameters
    >
    > ------------------------------------------------------------------------------
    > Preface
    > @@ -2283,4 +2284,21 @@ For example:
    > $ echo 0x7 > /proc/self/coredump_filter
    > $ ./some_program
    >
    > +2.16 /proc/sys/fs/types/ - File system type specific parameters
    > +----------------------------------------------------------------
    > +
    > +There's a separate directory /proc/sys/fs/types/<type>/ for each
    > +filesystem type, containing the following files:
    > +
    > +usermount_safe
    > +--------------
    > +
    > +Setting this to non-zero will allow filesystems of this type to be
    > +mounted by unprivileged users (note, that there are other
    > +prerequisites as well).
    > +
    > +Care should be taken when enabling this, since most
    > +filesystems haven't been designed with unprivileged mounting
    > +in mind.
    > +
    > ------------------------------------------------------------------------------
    >
    > --
    > -
    > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
    > the body of a message to majordomo@vger.kernel.org
    > More majordomo info at http://vger.kernel.org/majordomo-info.html


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