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SubjectRe: [PATCH] Exporting capability code/name pairs
Quoting KaiGai Kohei (kaigai@ak.jp.nec.com):
> This patch enables to export the code/name pairs of capabilities under
> /capability of securityfs.
>
> In the current libcap, it obtains the list of capabilities from header file
> on the build environment statically. However, it is not enough portable
> between different versions of kernels, because an already built libcap
> cannot have knowledge about new added capabilities.
>
> Dynamic collection of code/name pairs of capabilities will resolve this
> matter.
>
> But it is not perfect one. I have a bit concern about this patch now.
>
> 1. I want to generate cap_entries array from linux/capability.h
> automatically. Is there any good idea?
> 2. We have to mount securityfs explicitly, or using /etc/fstab.
> It can make a matter when we want to use this features
> in very early boot sequence.
>
> Any comment please.

I like the idea, but

> usage:
> -----------------------------------------------
> # mount -t securityfs none /sys/kernel/security
> # cd /sys/kernel/security/capability
> # ls
> cap_audit_control cap_kill cap_setpcap cap_sys_rawio
> cap_audit_write cap_lease cap_setuid cap_sys_resource
> cap_chown cap_linux_immutable cap_sys_admin cap_sys_time
> cap_dac_override cap_mknod cap_sys_boot cap_sys_tty_config
> cap_dac_read_search cap_net_admin cap_sys_chroot index
> cap_fowner cap_net_bind_service cap_sys_module version
> cap_fsetid cap_net_broadcast cap_sys_nice
> cap_ipc_lock cap_setfcap cap_sys_pacct
> cap_ipc_owner cap_setgid cap_sys_ptrace
> # cat cap_audit_write ; echo
> 29
> # cat cap_sys_chroot ; echo
> 18
> # cat version ; echo
> 0x19980330
> # cat index; echo
> 31
> #
>
> --
> OSS Platform Development Division, NEC
> KaiGai Kohei <kaigai@ak.jp.nec.com>
>
> Signed-off-by: KaiGai Kohei <kaigai@ak.jp.nec.com>
> ---
> capability.c | 127 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 127 insertions(+)
>
> diff --git a/kernel/capability.c b/kernel/capability.c
> index efbd9cd..5d9bf53 100644
> --- a/kernel/capability.c
> +++ b/kernel/capability.c
> @@ -245,3 +245,131 @@ int capable(int cap)
> return __capable(current, cap);
> }
> EXPORT_SYMBOL(capable);
> +
> +/*
> + * Capability code/name pair exporting
> + */
> +
> +/*
> + * capability code/name pairs are exported under /sys/security/capability/
> + */
> +struct cap_entry_data {
> + unsigned int code;
> + const char *name;
> +};
> +
> +static struct cap_entry_data cap_entries[] = {
> + /* max number of supported format */
> + { _LINUX_CAPABILITY_VERSION, "version" },
> + /* max number of capability */
> + { CAP_LAST_CAP, "index" },
> + /* list of capabilities */
> + { CAP_CHOWN, "cap_chown" },
> + { CAP_DAC_OVERRIDE, "cap_dac_override" },
> + { CAP_DAC_READ_SEARCH, "cap_dac_read_search" },
> + { CAP_FOWNER, "cap_fowner" },
> + { CAP_FSETID, "cap_fsetid" },
> + { CAP_KILL, "cap_kill" },
> + { CAP_SETGID, "cap_setgid" },
> + { CAP_SETUID, "cap_setuid" },
> + { CAP_SETPCAP, "cap_setpcap" },
> + { CAP_LINUX_IMMUTABLE, "cap_linux_immutable" },
> + { CAP_NET_BIND_SERVICE, "cap_net_bind_service" },
> + { CAP_NET_BROADCAST, "cap_net_broadcast" },
> + { CAP_NET_ADMIN, "cap_net_admin" },
> + { CAP_NET_RAW, "cap_net_admin" },
> + { CAP_IPC_LOCK, "cap_ipc_lock" },
> + { CAP_IPC_OWNER, "cap_ipc_owner" },
> + { CAP_SYS_MODULE, "cap_sys_module" },
> + { CAP_SYS_RAWIO, "cap_sys_rawio" },
> + { CAP_SYS_CHROOT, "cap_sys_chroot" },
> + { CAP_SYS_PTRACE, "cap_sys_ptrace" },
> + { CAP_SYS_PACCT, "cap_sys_pacct" },
> + { CAP_SYS_ADMIN, "cap_sys_admin" },
> + { CAP_SYS_BOOT, "cap_sys_boot" },
> + { CAP_SYS_NICE, "cap_sys_nice" },
> + { CAP_SYS_RESOURCE, "cap_sys_resource" },
> + { CAP_SYS_TIME, "cap_sys_time" },
> + { CAP_SYS_TTY_CONFIG, "cap_sys_tty_config" },
> + { CAP_MKNOD, "cap_mknod" },
> + { CAP_LEASE, "cap_lease" },
> + { CAP_AUDIT_WRITE, "cap_audit_write" },
> + { CAP_AUDIT_CONTROL, "cap_audit_control" },
> + { CAP_SETFCAP, "cap_setfcap" },
> + { CAP_MAC_OVERRIDE, "cap_mac_override" },
> + { CAP_MAC_ADMIN, "cap_mac_admin" },
> + { -1, NULL},
> +};

I don't like this duplication with the list in include/linux/capability.h.
Now when a new cap is added, it needs to be

1. added to capability.h
2. swapped as the new CAP_LAST_CAP in capability.h
3. added to this list...

Could you integrate the two lists (not sure how offhand), or at least
put them in the same place?

> +static ssize_t cap_entry_read(struct file *file, char __user *buffer,
> + size_t count, loff_t *ppos)
> +{
> + struct cap_entry_data *cap_entry;
> + size_t len, ofs = *ppos;
> + char tmp[32];
> + int rc;
> +
> + cap_entry = file->f_dentry->d_inode->i_private;
> + if (!cap_entry)
> + return -EINVAL;
> +
> + if (cap_entry == &cap_entries[0]) {
> + /* 'version' entry*/
> + snprintf(tmp, sizeof(tmp), "0x%08x", cap_entry->code);
> + } else {
> + snprintf(tmp, sizeof(tmp), "%u", cap_entry->code);
> + }
> + len = strlen(tmp);
> +
> + if (ofs >= len)
> + return 0;
> +
> + if (len - ofs < count)
> + count = len - ofs;
> +
> + rc = copy_to_user(buffer, tmp + ofs, count);
> + if (rc)
> + return rc;
> +
> + *ppos += count;
> + return count;
> +}
> +
> +const struct file_operations cap_entry_fops = {
> + .read = cap_entry_read,
> +};
> +
> +int __init cap_names_export(void)
> +{
> + struct dentry *d_caps, *f_caps[ARRAY_SIZE(cap_entries)];
> + int i;
> +
> + d_caps = securityfs_create_dir("capability", NULL);
> + if (!d_caps)
> + goto error0;
> +
> + memset(f_caps, 0, sizeof(f_caps));
> + for (i = 0; cap_entries[i].name; i++) {
> + f_caps[i] = securityfs_create_file(cap_entries[i].name, 0444,
> + d_caps, &cap_entries[i],
> + &cap_entry_fops);
> + if (!f_caps[i])
> + goto error1;
> + }
> + printk(KERN_NOTICE "capability code/name pairs are exported\n");
> + return 0;
> +
> +error1:
> + while (i > 0) {
> + i--;
> + securityfs_remove(f_caps[i]);
> + }
> + securityfs_remove(d_caps);
> +error0:
> + printk(KERN_ERR "Unable to export capability code/name pairs\n");
> +
> + return 0;
> +}
> +
> +__initcall(cap_names_export);


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