Messages in this thread | | | Date | Thu, 2 Dec 2021 08:52:37 -0500 | Subject | Re: [RFC 20/20] ima: Setup securityfs_ns for IMA namespace | From | Stefan Berger <> |
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On 12/2/21 08:18, Christian Brauner wrote: > On Tue, Nov 30, 2021 at 11:06:54AM -0500, Stefan Berger wrote: >> Setup securityfs_ns with symlinks, directories, and files for IMA >> namespacing support. The same directory structure that IMA uses on the >> host is also created for the namespacing case. >> >> Increment the user namespace's refcount_teardown value by '1' once >> securityfs_ns has been successfully setup since the initialization of the >> filesystem causes an additional reference to the user namespace to be >> taken. The early teardown function will delete the file system and release >> the additional reference. >> >> The securityfs_ns file and directory ownerships cannot be set when the >> filesystem is setup since at this point the user namespace has not been >> configured yet by the user and therefore the ownership mappings are not >> available, yet. Therefore, adjust the file and directory ownerships when >> an inode's function for determining the permissions of a file or directory >> is accessed. >> >> This filesystem can now be mounted as follows: >> >> mount -t securityfs_ns /sys/kernel/security/ /sys/kernel/security/ >> >> The following directories, symlinks, and files are then available. >> >> $ ls -l sys/kernel/security/ >> total 0 >> lr--r--r--. 1 nobody nobody 0 Nov 27 06:44 ima -> integrity/ima >> drwxr-xr-x. 3 nobody nobody 0 Nov 27 06:44 integrity >> >> $ ls -l sys/kernel/security/ima/ >> total 0 >> -r--r-----. 1 root root 0 Nov 27 06:44 ascii_runtime_measurements >> -r--r-----. 1 root root 0 Nov 27 06:44 binary_runtime_measurements >> -rw-------. 1 root root 0 Nov 27 06:44 policy >> -r--r-----. 1 root root 0 Nov 27 06:44 runtime_measurements_count >> -r--r-----. 1 root root 0 Nov 27 06:44 violations >> >> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com> >> --- >> include/linux/ima.h | 17 +++ >> security/integrity/ima/ima.h | 2 + >> security/integrity/ima/ima_fs.c | 178 ++++++++++++++++++++++- >> security/integrity/ima/ima_init_ima_ns.c | 6 +- >> security/integrity/ima/ima_ns.c | 4 +- >> 5 files changed, 203 insertions(+), 4 deletions(-) >> >> diff --git a/include/linux/ima.h b/include/linux/ima.h >> index fe08919df326..a2c5e516f706 100644 >> --- a/include/linux/ima.h >> +++ b/include/linux/ima.h >> @@ -221,6 +221,18 @@ struct ima_h_table { >> struct hlist_head queue[IMA_MEASURE_HTABLE_SIZE]; >> }; >> >> +enum { >> + IMAFS_DENTRY_INTEGRITY_DIR = 0, >> + IMAFS_DENTRY_DIR, >> + IMAFS_DENTRY_SYMLINK, >> + IMAFS_DENTRY_BINARY_RUNTIME_MEASUREMENTS, >> + IMAFS_DENTRY_ASCII_RUNTIME_MEASUREMENTS, >> + IMAFS_DENTRY_RUNTIME_MEASUREMENTS_COUNT, >> + IMAFS_DENTRY_VIOLATIONS, >> + IMAFS_DENTRY_IMA_POLICY, >> + IMAFS_DENTRY_LAST >> +}; >> + >> struct ima_namespace { >> struct kref kref; >> struct user_namespace *user_ns; >> @@ -267,6 +279,11 @@ struct ima_namespace { >> struct mutex ima_write_mutex; >> unsigned long ima_fs_flags; >> int valid_policy; >> + >> + struct dentry *dentry[IMAFS_DENTRY_LAST]; >> + struct vfsmount *mount; >> + int mount_count; >> + bool file_ownership_fixes_done; >> }; >> >> extern struct ima_namespace init_ima_ns; >> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h >> index bb9763cd5fb1..9bcd71bb716c 100644 >> --- a/security/integrity/ima/ima.h >> +++ b/security/integrity/ima/ima.h >> @@ -139,6 +139,8 @@ struct ns_status { >> /* Internal IMA function definitions */ >> int ima_init(void); >> int ima_fs_init(void); >> +int ima_fs_ns_init(struct ima_namespace *ns); >> +void ima_fs_ns_free(struct ima_namespace *ns); >> int ima_add_template_entry(struct ima_namespace *ns, >> struct ima_template_entry *entry, int violation, >> const char *op, struct inode *inode, >> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c >> index 6766bb8262f2..9a14be520268 100644 >> --- a/security/integrity/ima/ima_fs.c >> +++ b/security/integrity/ima/ima_fs.c >> @@ -22,6 +22,7 @@ >> #include <linux/parser.h> >> #include <linux/vmalloc.h> >> #include <linux/ima.h> >> +#include <linux/namei.h> >> >> #include "ima.h" >> >> @@ -436,8 +437,13 @@ static int ima_release_policy(struct inode *inode, struct file *file) >> >> ima_update_policy(ns); >> #if !defined(CONFIG_IMA_WRITE_POLICY) && !defined(CONFIG_IMA_READ_POLICY) >> - securityfs_remove(ima_policy); >> - ima_policy = NULL; >> + if (ns == &init_ima_ns) { >> + securityfs_remove(ima_policy); >> + ima_policy = NULL; >> + } else { >> + securityfs_ns_remove(ns->dentry[IMAFS_DENTRY_POLICY]); >> + ns->dentry[IMAFS_DENTRY_POLICY] = NULL; >> + } >> #elif defined(CONFIG_IMA_WRITE_POLICY) >> clear_bit(IMA_FS_BUSY, &ns->ima_fs_flags); >> #elif defined(CONFIG_IMA_READ_POLICY) >> @@ -509,3 +515,171 @@ int __init ima_fs_init(void) >> securityfs_remove(ima_policy); >> return -1; >> } >> + >> +/* >> + * Fix the ownership (uid/gid) of the dentry's that couldn't be set at the >> + * time of their creation because the user namespace wasn't configured, yet. >> + */ >> +static void ima_fs_ns_fixup_uid_gid(struct ima_namespace *ns) >> +{ >> + struct inode *inode; >> + size_t i; >> + >> + if (ns->file_ownership_fixes_done || >> + ns->user_ns->uid_map.nr_extents == 0) >> + return; >> + >> + ns->file_ownership_fixes_done = true; >> + for (i = 0; i < IMAFS_DENTRY_LAST; i++) { >> + if (!ns->dentry[i]) >> + continue; >> + inode = ns->dentry[i]->d_inode; >> + inode->i_uid = make_kuid(ns->user_ns, 0); >> + inode->i_gid = make_kgid(ns->user_ns, 0); >> + } >> +} >> + >> +/* Fix the permissions when a file is opened */ >> +int ima_fs_ns_permission(struct user_namespace *mnt_userns, struct inode *inode, >> + int mask) >> +{ >> + ima_fs_ns_fixup_uid_gid(get_current_ns()); > As noted later in the thread if this is required it means something is > buggy in the current code. That shouldn't be needed. I fixed this yesterday with late initialization: https://lkml.org/lkml/2021/12/1/1181 > > I think there's a more fundamental issue here. The correct way to do all > this would be to restructure securityfs at least how it works inside of > user namespaces. Currently, securityfs works like debugfs: a single > shared superblock that is pinned by each new inode that is created via: > > simple_pin_fs(&fs_type, &mount, &mount_count); > simple_release_fs(&mount, &mount_count); > > and each mount surfaces the same superblock. Ideally making securityfs > mountable inside of user namespaces should get you a new superblock. > Functions that create files for the ima ns would then be called inside > ->fill_super etc.
So this would be the wrong place to do it? I moved it there because this is called late (upon mounting) when the configuration of the user namespace has completed.
static int securityfs_ns_init_fs_context(struct fs_context *fc) { int rc;
if (fc->user_ns->ima_ns->late_fs_init) { rc = fc->user_ns->ima_ns->late_fs_init(fc->user_ns); if (rc) return rc; } fc->ops = &securityfs_ns_context_ops; return 0; }
Stefan
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