[PATCH] 2.6.25: Filesystem capabilities 0.18

From: Olaf Dietsche
Date: Mon May 12 2008 - 17:00:33 EST

This patch implements filesystem capabilities. It allows to
run privileged executables without the need for suid root.

Changes:
- updated to 2.6.25

This patch is available at:
<http://www.olafdietsche.de/linux/capability/>

Regards, Olaf.
diff --git a/fs/Kconfig b/fs/Kconfig
index c509123..51f9a95 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -1445,6 +1445,71 @@ config QNX4FS_RW
It's currently broken, so for now:
answer N.

+config FS_CAPABILITIES
+ bool "Filesystem capabilities (Experimental)"
+ depends on EXPERIMENTAL
+ default n
+ help
+ This implementation is likely _not_ POSIX compatible.
+
+ If you say Y here, you will be able to grant selective privileges to
+ executables on a needed basis. This means for some executables, there
+ is no need anymore to run as root or as a suid root binary.
+
+ For example, you may drop the SUID bit from ping and grant the
+ CAP_NET_RAW capability:
+ # chmod u-s /bin/ping
+ # chcap cap_net_raw=ep /bin/ping
+
+ Another use would be to run system daemons with their own uid:
+ # chcap cap_net_bind_service=ei /usr/sbin/named
+ This sets the effective and inheritable capabilities of named.
+
+ In your startup script:
+ inhcaps cap_net_bind_service=i bind:bind /usr/sbin/named
+
+ This sets the inheritable set to CAP_NET_BIND_SERVICE, which is
+ needed in order to bind to port 53, and runs named as user bind
+ with group bind.
+
+ This allows running named with needed restricted privileges, if the
+ parent process (root) owns them already. When started by regular
+ users, named runs without any privileges.
+
+ WARNING:
+ resize2fs(8) might relocate inodes and thus break fs capabilities.
+ For this to work you must dump the capability db before you resize
+ and restore the db afterwards.
+
+ For user space tools see:
+ <http://www.olafdietsche.de/linux/capability/>
+
+ For libcap and an alternative implementation, based on extended
+ attributes, see:
+ <http://www.kernel.org/pub/linux/libs/security/linux-privs/>
+
+ If you're unsure, say N.
+
+config LIBC_ENABLE_SECURE_HACK
+ bool "Disable LD_PRELOAD on privileged executables"
+ depends on FS_CAPABILITIES
+ default n
+ help
+ LD_PRELOAD is a glibc feature, which allows to override system
+ library functions. But this means also a security hole, through
+ which an attacker might gain unauthorized privileges. This is
+ already prevented for SUID and SGID binaries.
+
+ Older GNU libc (pre 2.3.6) didn't know about filesystem
+ capabilities and didn't disable LD_PRELOAD for privileged
+ executables, which are not SUID or SGID. This hack sets the
+ group id to an invalid value and tricks GNU libc into thinking,
+ this is a SGID binary (unless it is already SUID and/or SGID).
+
+ However, this may break some programs.
+
+ If your libc is older than 2.3.6, say Y.
+
config ROMFS_FS
tristate "ROM file system support"
depends on BLOCK
diff --git a/fs/Makefile b/fs/Makefile
index 1e7a11b..225c90e 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -64,7 +64,8 @@ obj-y += devpts/

obj-$(CONFIG_PROFILING) += dcookies.o
obj-$(CONFIG_DLM) += dlm/
-
+obj-$(CONFIG_FS_CAPABILITIES) += fscaps.o
+
# Do not add any filesystems before this line
obj-$(CONFIG_REISERFS_FS) += reiserfs/
obj-$(CONFIG_EXT3_FS) += ext3/ # Before ext2 so root fs can be ext3
diff --git a/fs/attr.c b/fs/attr.c
index 966b73e..8897bf8 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -14,6 +14,7 @@
#include <linux/fcntl.h>
#include <linux/quotaops.h>
#include <linux/security.h>
+#include <linux/fscaps.h>

/* Taken over from the old code... */

@@ -177,8 +178,12 @@ int notify_change(struct dentry * dentry, struct iattr * attr)
if (ia_valid & ATTR_SIZE)
up_write(&dentry->d_inode->i_alloc_sem);

- if (!error)
+ if (!error) {
+ if (ia_valid & (ATTR_KILL_SUID | ATTR_KILL_SGID))
+ fscap_drop(inode);
+
fsnotify_change(dentry, ia_valid);
+ }

return error;
}
diff --git a/fs/fscaps.c b/fs/fscaps.c
new file mode 100644
index 0000000..27a12f3
--- /dev/null
+++ b/fs/fscaps.c
@@ -0,0 +1,314 @@
+/*
+ * Copyright (c) 2002 Olaf Dietsche
+ *
+ * Filesystem capabilities for linux.
+ */
+
+#include <linux/fscaps.h>
+#include <linux/module.h>
+#include <linux/binfmts.h>
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include <linux/slab.h>
+#include <linux/mount.h>
+#include <asm/uaccess.h>
+
+struct fscap_info {
+ struct vfsmount *mnt;
+ struct dentry *dentry;
+ struct inode_operations rootdir_envelop;
+ const struct inode_operations *rootdir_iops;
+ struct inode_operations cap_envelop;
+ const struct inode_operations *cap_iops;
+};
+
+static char __capname[] = ".capabilities";
+
+static int __is_capname(const char *name)
+{
+ if (*name != __capname[0])
+ return 0;
+
+ return !strcmp(name, __capname);
+}
+
+static int __is_capentry(struct dentry *dentry)
+{
+ return dentry == dentry->d_sb->s_fscaps->dentry;
+}
+
+static int __cap_permission(struct inode *inode, int mask, struct nameidata *nd)
+{
+ const struct inode_operations *iops;
+ if ((mask & MAY_WRITE) && !capable(CAP_SETFCAP))
+ return -EPERM;
+
+ iops = inode->i_sb->s_fscaps->cap_iops;
+ if (iops && iops->permission)
+ return iops->permission(inode, mask, nd);
+
+ return generic_permission(inode, mask, NULL);
+}
+
+static void __info_cap_release(struct fscap_info *info)
+{
+ if (info->dentry) {
+ struct inode *inode = info->dentry->d_inode;
+ if (inode)
+ inode->i_op = info->cap_iops;
+
+ dput(info->dentry);
+ }
+}
+
+static void __info_cap_init(struct fscap_info *info, struct dentry *dentry)
+{
+ struct inode *inode;
+ const struct inode_operations *iops;
+ __info_cap_release(info);
+
+ info->dentry = dget(dentry);
+ if (!dentry)
+ return;
+
+ inode = dentry->d_inode;
+ if (!inode) {
+ printk(KERN_WARNING "%s: negative dentry. Disabling capabilities on %s.\n", __FUNCTION__, info->mnt->mnt_mountpoint->d_name.name);
+ dput(info->dentry);
+ info->dentry = NULL;
+ return;
+ }
+
+ info->cap_iops = iops = inode->i_op;
+ memset(&info->cap_envelop, 0, sizeof(info->cap_envelop));
+ if (iops)
+ info->cap_envelop = *iops;
+
+ info->cap_envelop.permission = __cap_permission;
+ inode->i_op = &info->cap_envelop;
+}
+
+static int __rootdir_create(struct inode *dir, struct dentry *dentry, int mode, struct nameidata *nd)
+{
+ const struct inode_operations *iops;
+ int err, iscapdb = __is_capname(dentry->d_name.name);
+ if (iscapdb && !capable(CAP_SETFCAP))
+ return -EPERM;
+
+ iops = dir->i_sb->s_fscaps->rootdir_iops;
+ err = iops->create(dir, dentry, mode, nd);
+ if (!err && iscapdb)
+ __info_cap_init(dir->i_sb->s_fscaps, dentry);
+
+ return err;
+}
+
+static int __rootdir_link(struct dentry *old_dentry, struct inode *dir,
+ struct dentry *new_dentry)
+{
+ const struct inode_operations *iops;
+ int err, iscapdb = __is_capname(new_dentry->d_name.name);
+ if (iscapdb && !capable(CAP_SETFCAP))
+ return -EPERM;
+
+ iops = dir->i_sb->s_fscaps->rootdir_iops;
+ err = iops->link(old_dentry, dir, new_dentry);
+ if (!err && iscapdb)
+ __info_cap_init(dir->i_sb->s_fscaps, new_dentry);
+
+ return err;
+}
+
+static int __rootdir_unlink(struct inode *dir, struct dentry *dentry)
+{
+ const struct inode_operations *iops;
+ int err, iscapdb = __is_capentry(dentry);
+ if (iscapdb && !capable(CAP_SETFCAP))
+ return -EPERM;
+
+ iops = dir->i_sb->s_fscaps->rootdir_iops;
+ err = iops->unlink(dir, dentry);
+ if (!err && iscapdb)
+ __info_cap_init(dir->i_sb->s_fscaps, NULL);
+
+ return err;
+}
+
+static int __rootdir_symlink(struct inode *dir, struct dentry *dentry, const char *oldname)
+{
+ const struct inode_operations *iops;
+ if (__is_capname(dentry->d_name.name))
+ return -EPERM;
+
+ iops = dir->i_sb->s_fscaps->rootdir_iops;
+ return iops->symlink(dir, dentry, oldname);
+}
+
+static int __rootdir_rename(struct inode *old_dir, struct dentry *old_dentry,
+ struct inode *new_dir, struct dentry *new_dentry)
+{
+ const struct inode_operations *iops;
+ if (__is_capentry(old_dentry) || __is_capname(new_dentry->d_name.name))
+ return -EPERM;
+
+ iops = old_dir->i_sb->s_fscaps->rootdir_iops;
+ return iops->rename(old_dir, old_dentry, new_dir, new_dentry);
+}
+
+static void __info_rootdir_release(struct fscap_info *info)
+{
+ struct inode *inode = info->mnt->mnt_sb->s_root->d_inode;
+ if (inode) {
+ inode->i_op = info->rootdir_iops;
+ }
+}
+
+static void __info_rootdir_init(struct fscap_info *info, struct inode *dir)
+{
+ const struct inode_operations *iops = dir->i_op;
+ info->rootdir_iops = iops;
+ if (iops) {
+ info->rootdir_envelop = *iops;
+ info->rootdir_envelop.create = iops->create ? __rootdir_create : 0;
+ info->rootdir_envelop.link = iops->link ? __rootdir_link : 0;
+ info->rootdir_envelop.unlink = iops->unlink ? __rootdir_unlink : 0;
+ info->rootdir_envelop.symlink = iops->symlink ? __rootdir_symlink : 0;
+ info->rootdir_envelop.rename = iops->rename ? __rootdir_rename : 0;
+ dir->i_op = &info->rootdir_envelop;
+ }
+}
+
+static void __info_init(struct vfsmount *mnt, struct dentry *dentry)
+{
+ struct fscap_info *info = kmalloc(sizeof(struct fscap_info), GFP_KERNEL);
+ if (info) {
+ info->mnt = mnt;
+ info->dentry = NULL;
+ __info_rootdir_init(info, mnt->mnt_sb->s_root->d_inode);
+ __info_cap_init(info, dentry);
+ }
+
+ mnt->mnt_sb->s_fscaps = info;
+}
+
+static void __info_release(struct fscap_info *info)
+{
+ if (info) {
+ __info_cap_release(info);
+ __info_rootdir_release(info);
+ kfree(info);
+ }
+}
+
+static inline struct fscap_info *__info_lookup(struct super_block *sb)
+{
+ return sb->s_fscaps;
+}
+
+static int __fscap_lookup(struct vfsmount *mnt, struct nameidata *nd)
+{
+ return vfs_path_lookup(mnt->mnt_sb->s_root, mnt, __capname, 0, nd);
+}
+
+static struct file *__fscap_open(struct dentry *dentry, struct vfsmount *mnt, int flags)
+{
+ if (mnt->mnt_flags & MNT_NOSUID)
+ return ERR_PTR(-EPERM);
+
+ dentry = dget(dentry);
+ mnt = mntget(mnt);
+ return dentry_open(dentry, mnt, flags);
+}
+
+static void __fscap_read(struct file *filp, struct linux_binprm *bprm)
+{
+ __u32 fscaps[3][4];
+ unsigned long ino = bprm->file->f_dentry->d_inode->i_ino;
+ int i, n = kernel_read(filp, ino * sizeof(fscaps), (char *) fscaps, sizeof(fscaps));
+ if (n == sizeof(fscaps)) {
+ for (i = 0; i < _LINUX_CAPABILITY_U32S; ++i) {
+ bprm->cap_effective.cap[i] = fscaps[0][i];
+ bprm->cap_inheritable.cap[i] = fscaps[1][i];
+ bprm->cap_permitted.cap[i] = fscaps[2][i];
+ }
+ }
+}
+
+static int kernel_write(struct file *file, unsigned long offset,
+ char *addr, unsigned long count)
+{
+ mm_segment_t old_fs;
+ loff_t pos = offset;
+ int result;
+
+ old_fs = get_fs();
+ set_fs(get_ds());
+ result = vfs_write(file, addr, count, &pos);
+ set_fs(old_fs);
+ return result;
+}
+
+static void __fscap_drop(struct file *filp, struct inode *inode)
+{
+ __u32 fscaps[3][4];
+ unsigned long ino = inode->i_ino;
+ int n = kernel_read(filp, ino * sizeof(fscaps), (char *) fscaps, sizeof(fscaps));
+ if (n == sizeof(fscaps) && (fscaps[0][0] || fscaps[1][0] || fscaps[2][0])) {
+ memset(fscaps, 0, sizeof(fscaps));
+ kernel_write(filp, ino * sizeof(fscaps), (char *) fscaps, sizeof(fscaps));
+ }
+}
+
+void fscap_mount(struct vfsmount *mnt)
+{
+ struct nameidata nd;
+ if (__info_lookup(mnt->mnt_sb))
+ return;
+
+ if (__fscap_lookup(mnt, &nd)) {
+ __info_init(mnt, NULL);
+ } else {
+ __info_init(mnt, nd.path.dentry);
+ path_put(&nd.path);
+ }
+}
+
+void fscap_umount(struct super_block *sb)
+{
+ struct fscap_info *info = __info_lookup(sb);
+ __info_release(info);
+ sb->s_fscaps = NULL;
+}
+
+void fscap_read(struct linux_binprm *bprm)
+{
+ struct file *filp;
+ struct fscap_info *info = __info_lookup(bprm->file->f_vfsmnt->mnt_sb);
+ if (!info || !info->dentry)
+ return;
+
+ filp = __fscap_open(info->dentry, info->mnt, O_RDONLY);
+ if (filp && !IS_ERR(filp)) {
+ __fscap_read(filp, bprm);
+ filp_close(filp, 0);
+ }
+}
+
+void fscap_drop(struct inode *inode)
+{
+ struct file *filp;
+ struct fscap_info *info = __info_lookup(inode->i_sb);
+ if (!info || !info->dentry)
+ return;
+
+ filp = __fscap_open(info->dentry, info->mnt, O_RDWR);
+ if (filp && !IS_ERR(filp)) {
+ __fscap_drop(filp, inode);
+ filp_close(filp, 0);
+ }
+}
+
+EXPORT_SYMBOL(fscap_mount);
+EXPORT_SYMBOL(fscap_umount);
+EXPORT_SYMBOL(fscap_read);
+EXPORT_SYMBOL(fscap_drop);
diff --git a/fs/namespace.c b/fs/namespace.c
index 94f026e..ab37237 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -26,6 +26,7 @@
#include <linux/mount.h>
#include <linux/ramfs.h>
#include <linux/log2.h>
+#include <linux/fscaps.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
#include "pnode.h"
@@ -1194,6 +1195,8 @@ int do_add_mount(struct vfsmount *newmnt, struct nameidata *nd,
if ((err = graft_tree(newmnt, nd)))
goto unlock;

+ fscap_mount(newmnt);
+
if (fslist) /* add to the specified expiration list */
list_add_tail(&newmnt->mnt_expire, fslist);

diff --git a/fs/open.c b/fs/open.c
index 3fa4e4f..1ba2251 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -27,6 +27,7 @@
#include <linux/rcupdate.h>
#include <linux/audit.h>
#include <linux/falloc.h>
+#include <linux/fscaps.h>

int vfs_statfs(struct dentry *dentry, struct kstatfs *buf)
{
@@ -780,6 +781,9 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
}
}

+ if (flags & O_CREAT)
+ fscap_drop(inode);
+
return f;

cleanup_all:
diff --git a/fs/super.c b/fs/super.c
index 09008db..9b50a36 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -37,6 +37,7 @@
#include <linux/idr.h>
#include <linux/kobject.h>
#include <linux/mutex.h>
+#include <linux/fscaps.h>
#include <asm/uaccess.h>


@@ -90,6 +91,7 @@ static struct super_block *alloc_super(struct file_system_type *type)
s->s_qcop = sb_quotactl_ops;
s->s_op = &default_op;
s->s_time_gran = 1000000000;
+ s->s_fscaps = NULL;
}
out:
return s;
@@ -178,6 +180,7 @@ void deactivate_super(struct super_block *s)
s->s_count -= S_BIAS-1;
spin_unlock(&sb_lock);
DQUOT_OFF(s);
+ fscap_umount(s);
down_write(&s->s_umount);
fs->kill_sb(s);
put_filesystem(fs);
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index b7fc55e..757600e 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -37,8 +37,12 @@ struct linux_binprm{
int sh_bang;
struct file * file;
int e_uid, e_gid;
+#ifdef CONFIG_FS_CAPABILITIES
+ kernel_cap_t cap_inheritable, cap_permitted, cap_effective;
+#else
kernel_cap_t cap_inheritable, cap_permitted;
bool cap_effective;
+#endif
void *security;
int argc, envc;
char * filename; /* Name of binary as seen by procps */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b84b848..dac9a2b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1015,6 +1015,7 @@ struct super_block {
struct mtd_info *s_mtd;
struct list_head s_instances;
struct quota_info s_dquot; /* Diskquota specific options */
+ struct fscap_info *s_fscaps; /* Filesystem capability stuff */

int s_frozen;
wait_queue_head_t s_wait_unfrozen;
diff --git a/include/linux/fscaps.h b/include/linux/fscaps.h
new file mode 100644
index 0000000..9046c15
--- /dev/null
+++ b/include/linux/fscaps.h
@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2002 Olaf Dietsche
+ *
+ * Filesystem capabilities for linux.
+ */
+
+#ifndef _LINUX_FS_CAPS_H
+#define _LINUX_FS_CAPS_H
+
+struct vfsmount;
+struct super_block;
+struct linux_binprm;
+struct inode;
+
+#if defined(CONFIG_FS_CAPABILITIES)
+extern void fscap_mount(struct vfsmount *mnt);
+extern void fscap_umount(struct super_block *sb);
+extern void fscap_read(struct linux_binprm *bprm);
+extern void fscap_drop(struct inode *inode);
+#else
+/* !CONFIG_FS_CAPABILITIES */
+static inline void fscap_mount(struct vfsmount *mnt) {}
+static inline void fscap_umount(struct super_block *sb) {}
+static inline void fscap_read(struct linux_binprm *bprm) {}
+static inline void fscap_drop(struct inode *inode) {}
+#endif
+
+#endif
diff --git a/security/commoncap.c b/security/commoncap.c
index 06d5c94..cd39d94 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -24,6 +24,7 @@
#include <linux/hugetlb.h>
#include <linux/mount.h>
#include <linux/sched.h>
+#include <linux/fscaps.h>

/* Global security state */

@@ -160,7 +161,11 @@ static inline void bprm_clear_caps(struct linux_binprm *bprm)
{
cap_clear(bprm->cap_inheritable);
cap_clear(bprm->cap_permitted);
+#ifdef CONFIG_FS_CAPABILITIES
+ cap_clear(bprm->cap_effective);
+#else
bprm->cap_effective = false;
+#endif
}

#ifdef CONFIG_SECURITY_FILE_CAPABILITIES
@@ -291,6 +296,7 @@ int cap_inode_killpriv(struct dentry *dentry)
static inline int get_file_caps(struct linux_binprm *bprm)
{
bprm_clear_caps(bprm);
+ fscap_read(bprm);
return 0;
}
#endif
@@ -318,7 +324,11 @@ int cap_bprm_set_security (struct linux_binprm *bprm)
cap_set_full (bprm->cap_permitted);
}
if (bprm->e_uid == 0)
+#ifdef CONFIG_FS_CAPABILITIES
+ cap_set_full (bprm->cap_effective);
+#else
bprm->cap_effective = true;
+#endif
}

return ret;
@@ -350,6 +360,10 @@ void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
current->cap_permitted);
}
}
+#ifdef CONFIG_LIBC_ENABLE_SECURE_HACK
+ if (bprm->e_uid == current->uid && bprm->e_gid == current->gid)
+ current->gid = -1;
+#endif
}

current->suid = current->euid = current->fsuid = bprm->e_uid;
@@ -360,10 +374,15 @@ void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
* capability rules */
if (!is_global_init(current)) {
current->cap_permitted = new_permitted;
+#ifdef CONFIG_FS_CAPABILITIES
+ current->cap_effective =
+ cap_intersect (new_permitted, bprm->cap_effective);
+#else
if (bprm->cap_effective)
current->cap_effective = new_permitted;
else
cap_clear(current->cap_effective);
+#endif
}

/* AUD: Audit candidate if current->cap_effective is set */
@@ -374,7 +393,11 @@ void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
int cap_bprm_secureexec (struct linux_binprm *bprm)
{
if (current->uid != 0) {
+#ifdef CONFIG_FS_CAPABILITIES
+ if (!cap_isclear(current->cap_permitted))
+#else
if (bprm->cap_effective)
+#endif
return 1;
if (!cap_isclear(bprm->cap_permitted))
return 1;