> On Sat, 19 Oct 2002, Olaf Dietsche wrote:
>
> mount --bind my_file /usr/.capabilities
This is still open.
>> > ditto for owner of
>> > root directory on some filesystem.
>>
>> Which is a problem for foreign (network) filesystems only. Should be
>> solvable with a mount option (i.e. mount -o nocaps ...).
I use option nosuid for now.
>> > And there is no way to recognize
>> > that file as such, so additional checks on write(), mount(), unlink().
>> > etc. are not possible.
>>
>> Depends on, wether I want to recognize it and do these checks. Anyway,
>> could be solved with a mount option too or something like quotactl(2)
>> maybe.
>
> Ahem. You had made several capabilities equivalent to "everything".
> E.g. "anyone who can override checks in chown() can set arbitrary
> capabilities", etc. Which changes model big way and makes the affected
> capabilities pretty much useless - they can be elevated to any other
> capability.
Which is nothing new, how I learnt recently: CAP_SYS_RAWIO,
CAP_SYS_MODULE for example, not to mention CAP_SETPCAP. But maybe
pinning the .capabilities inode in memory and providing an appropriate
i_op could be a solution?
> mount --bind /usr/bin /mnt
> Suddenly /mnt/foo and /usr/bin/foo (same file) have different capabilities.
I use super_block->s_root, so this is no problem anymore.
Now it drops capabilities, when a chown() or open() is done.
Well, here is my next try against 2.5.44. It's slightly better than
before, boots and seems to work as expected :-)
Regards, Olaf.
diff -urN a/fs/Config.in b/fs/Config.in
--- a/fs/Config.in Wed Oct 16 09:23:41 2002
+++ b/fs/Config.in Thu Oct 24 00:11:51 2002
@@ -108,6 +108,8 @@
define_bool CONFIG_QUOTACTL y
fi
+dep_bool 'Filesystem capabilities (Experimental)' CONFIG_FS_CAPABILITIES $CONFIG_EXPERIMENTAL
+
if [ "$CONFIG_NET" = "y" ]; then
mainmenu_option next_comment
diff -urN a/fs/Makefile b/fs/Makefile
--- a/fs/Makefile Sat Oct 19 13:52:46 2002
+++ b/fs/Makefile Thu Oct 24 00:11:51 2002
@@ -6,7 +6,7 @@
#
export-objs := open.o dcache.o buffer.o bio.o inode.o dquot.o mpage.o aio.o \
- fcntl.o read_write.o dcookies.o
+ fcntl.o read_write.o dcookies.o fscaps.o
obj-y := open.o read_write.o devices.o file_table.o buffer.o \
bio.o super.o block_dev.o char_dev.o stat.o exec.o pipe.o \
@@ -41,7 +41,8 @@
obj-y += devpts/
obj-$(CONFIG_PROFILING) += dcookies.o
-
+obj-$(CONFIG_FS_CAPABILITIES) += fscaps.o
+
# Do not add any filesystems before this line
obj-$(CONFIG_EXT3_FS) += ext3/ # Before ext2 so root fs can be ext3
obj-$(CONFIG_JBD) += jbd/
diff -urN a/fs/attr.c b/fs/attr.c
--- a/fs/attr.c Sat Oct 5 18:44:20 2002
+++ b/fs/attr.c Thu Oct 24 00:11:51 2002
@@ -13,6 +13,7 @@
#include <linux/fcntl.h>
#include <linux/quotaops.h>
#include <linux/security.h>
+#include <linux/fscaps.h>
/* Taken over from the old code... */
@@ -170,6 +171,9 @@
}
if (!error) {
unsigned long dn_mask = setattr_mask(ia_valid);
+ if (ia_valid & (ATTR_KILL_SUID | ATTR_KILL_SGID))
+ fscap_drop(dentry);
+
if (dn_mask)
dnotify_parent(dentry, dn_mask);
}
diff -urN a/fs/fscaps.c b/fs/fscaps.c
--- a/fs/fscaps.c Thu Jan 1 01:00:00 1970
+++ b/fs/fscaps.c Thu Oct 24 13:44:37 2002
@@ -0,0 +1,102 @@
+/*
+ * 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 <asm/uaccess.h>
+
+static int __fscap_lookup(struct vfsmount *mnt, struct nameidata *nd)
+{
+ static char name[] = ".capabilities";
+ nd->mnt = mntget(mnt);
+ nd->dentry = dget(mnt->mnt_sb->s_root);
+ nd->flags = 0;
+ return path_walk(name, nd);
+}
+
+static struct file *__fscap_open(struct dentry *de, struct vfsmount *mnt, int flags)
+{
+ struct inode *inode = de->d_inode;
+ if (mnt->mnt_flags & MNT_NOSUID)
+ return ERR_PTR(-EPERM);
+
+ if (inode->i_uid != 0 || inode->i_gid != 0)
+ return ERR_PTR(-EPERM);
+
+ if ((inode->i_mode & 077) != 0)
+ return ERR_PTR(-EACCES);
+
+ return dentry_open(de, mnt, flags);
+}
+
+static void __fscap_read(struct file *filp, struct linux_binprm *bprm)
+{
+ __u32 fscaps[3];
+ unsigned long ino = bprm->file->f_dentry->d_inode->i_ino;
+ int n = kernel_read(filp, ino * sizeof(fscaps), (char *) fscaps, sizeof(fscaps));
+ if (n == sizeof(fscaps)) {
+ bprm->cap_effective = fscaps[0];
+ bprm->cap_inheritable = fscaps[1];
+ bprm->cap_permitted = fscaps[2];
+ }
+}
+
+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 dentry *de)
+{
+ __u32 fscaps[3];
+ unsigned long ino = de->d_inode->i_ino;
+ int n = kernel_read(filp, ino * sizeof(fscaps), (char *) fscaps, sizeof(fscaps));
+ if (n == sizeof(fscaps) && (fscaps[0] || fscaps[1] || fscaps[2])) {
+ fscaps[0] = fscaps[1] = fscaps[2] = 0;
+ kernel_write(filp, ino * sizeof(fscaps), (char *) fscaps, sizeof(fscaps));
+ }
+}
+
+void fscap_read(struct linux_binprm *bprm)
+{
+ struct nameidata nd;
+ int err = __fscap_lookup(bprm->file->f_vfsmnt, &nd);
+ if (!err) {
+ struct file *filp = __fscap_open(nd.dentry, nd.mnt, O_RDONLY);
+ if (filp && !IS_ERR(filp)) {
+ __fscap_read(filp, bprm);
+ filp_close(filp, 0);
+ }
+ }
+}
+
+void fscap_drop(struct dentry *de)
+{
+ struct nameidata nd;
+ int err = __fscap_lookup(de->d_sb->s_rootmnt, &nd);
+ if (!err) {
+ struct file *filp = __fscap_open(nd.dentry, nd.mnt, O_RDWR);
+ if (filp && !IS_ERR(filp)) {
+ __fscap_drop(filp, de);
+ filp_close(filp, 0);
+ }
+ }
+}
+
+EXPORT_SYMBOL(fscap_read);
+EXPORT_SYMBOL(fscap_drop);
diff -urN a/fs/open.c b/fs/open.c
--- a/fs/open.c Wed Oct 16 09:23:41 2002
+++ b/fs/open.c Thu Oct 24 13:53:25 2002
@@ -17,6 +17,7 @@
#include <linux/namei.h>
#include <linux/backing-dev.h>
#include <linux/security.h>
+#include <linux/fscaps.h>
#include <asm/uaccess.h>
@@ -665,6 +666,9 @@
goto cleanup_all;
}
}
+
+ if (flags & O_CREAT)
+ fscap_drop(dentry);
return f;
diff -urN a/fs/super.c b/fs/super.c
--- a/fs/super.c Sat Oct 5 18:45:22 2002
+++ b/fs/super.c Thu Oct 24 00:11:51 2002
@@ -72,6 +72,7 @@
s->s_maxbytes = MAX_NON_LFS;
s->dq_op = sb_dquot_ops;
s->s_qcop = sb_quotactl_ops;
+ s->s_rootmnt = NULL;
}
out:
return s;
@@ -619,6 +620,7 @@
sb = type->get_sb(type, flags, name, data);
if (IS_ERR(sb))
goto out_mnt;
+ sb->s_rootmnt = mnt;
mnt->mnt_sb = sb;
mnt->mnt_root = dget(sb->s_root);
mnt->mnt_mountpoint = sb->s_root;
diff -urN a/include/linux/fs.h b/include/linux/fs.h
--- a/include/linux/fs.h Sat Oct 19 13:52:47 2002
+++ b/include/linux/fs.h Thu Oct 24 00:11:51 2002
@@ -650,6 +650,7 @@
unsigned long s_flags;
unsigned long s_magic;
struct dentry *s_root;
+ struct vfsmount *s_rootmnt;
struct rw_semaphore s_umount;
struct semaphore s_lock;
int s_count;
diff -urN a/include/linux/fscaps.h b/include/linux/fscaps.h
--- a/include/linux/fscaps.h Thu Jan 1 01:00:00 1970
+++ b/include/linux/fscaps.h Thu Oct 24 13:44:52 2002
@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2002 Olaf Dietsche
+ *
+ * Filesystem capabilities for linux.
+ */
+
+#ifndef _LINUX_FS_CAPS_H
+#define _LINUX_FS_CAPS_H
+
+#include <linux/config.h>
+
+struct linux_binprm;
+struct dentry;
+
+#if defined(CONFIG_FS_CAPABILITIES) || defined(CONFIG_FS_CAPABILITIES_MODULE)
+extern void fscap_read(struct linux_binprm *bprm);
+extern void fscap_drop(struct dentry *de);
+#else
+/* !CONFIG_FS_CAPABILITIES */
+static inline void fscap_read(struct linux_binprm *bprm) {}
+static inline void fscap_drop(struct dentry *de) {}
+#endif
+
+#endif
diff -urN a/security/capability.c b/security/capability.c
--- a/security/capability.c Sat Oct 19 13:52:48 2002
+++ b/security/capability.c Thu Oct 24 00:11:51 2002
@@ -18,6 +18,7 @@
#include <linux/smp_lock.h>
#include <linux/skbuff.h>
#include <linux/netlink.h>
+#include <linux/fscaps.h>
/* flag to keep track of how we were registered */
static int secondary;
@@ -119,10 +120,11 @@
{
/* Copied from fs/exec.c:prepare_binprm. */
- /* We don't have VFS support for capabilities yet */
cap_clear (bprm->cap_inheritable);
cap_clear (bprm->cap_permitted);
cap_clear (bprm->cap_effective);
+
+ fscap_read(bprm);
/* To support inheritance of root-permissions and suid-root
* executables under compatibility mode, we raise all three
-
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