Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 9 Dec 2021 10:00:59 -0500 | Subject | Re: [PATCH v5 15/16] ima: Move dentries into ima_namespace | From | Stefan Berger <> |
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On 12/9/21 09:41, Christian Brauner wrote: > On Thu, Dec 09, 2021 at 03:37:49PM +0100, Christian Brauner wrote: >> On Thu, Dec 09, 2021 at 03:34:28PM +0100, Christian Brauner wrote: >>> On Wed, Dec 08, 2021 at 05:18:17PM -0500, Stefan Berger wrote: >>>> Move the dentries into the ima_namespace for reuse by virtualized >>>> SecurityFS. Implement function freeing the dentries in order of >>>> files and symlinks before directories. >>>> >>>> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com> >>>> --- >>> This doesn't work as implemented, I think. >>> >>> What I would have preferred and what I tried to explain in the earlier >>> review was: >>> Keep the dentry stashing global since it is only needed for init_ima_ns. >>> Then struct ima_namespace becomes way smaller and simpler. >>> If you do that then it makes sense to remove the additional dget() in >>> securityfs_create_dentry() for non-init_ima_ns. >>> Then you can rely on auto-cleanup in .kill_sb() or on >>> ima_securityfs_init() failure and you only need to call >>> ima_fs_ns_free_dentries() if ns != init_ima_ns. > s/ns != init_ima_ns/ns == init_ima_ns/ > >>> IIuc, it seems you're currently doing one dput() too many since you're >>> calling securityfs_remove() in the error path for non-init_ima_ns which >>> relies on the previous increased dget() which we removed.
I thought that securityfs_remove() will now simply influence when a dentry is removed and freed. If we call it in the error cleanup path in non-init_user_ns case it would go away right there and leave nothing to do for .kill_sb() while an additional dget() would require the cleanup as well but do another cleanup then in .kill_sb() since that brings the reference count to 0 via the dput()s that it does. Am I wrong on this?
>> If you really want to move the dentry stashing into struct ima_namespace >> even though it's really unnecessary then you may as well not care about >> the auto-cleanup and keep that additional ima_fs_ns_free_dentries(ns) >> call in .kill_sb(). But I really think not dragging dentry stashing into >> struct ima_namespace is the correct way to go about this.
I moved the dentries into the ima_namespace so that each namespace holds a pointer to the dentries it owns and isolates them. We certainly wouldn't want to have IMA namespaces write over the current static variables and create a mess with what these are pointing to ( https://elixir.bootlin.com/linux/latest/source/security/integrity/ima/ima_fs.c#L359 ) and possible race conditions when doing parallel initialization (if that's possible at all). This also reduces the code size and we don't need two different implementations for init_user_ns and non-init_user_ns. So I don't quite understand whey we wouldn't want to have the dentries isolated via ima_namespace?
>> >>>> include/linux/ima.h | 13 ++++++ >>>> security/integrity/ima/ima_fs.c | 72 ++++++++++++++++++--------------- >>>> 2 files changed, 52 insertions(+), 33 deletions(-) >>>> >>>> diff --git a/include/linux/ima.h b/include/linux/ima.h >>>> index 3aaf6e806db4..4dd64e318b15 100644 >>>> --- a/include/linux/ima.h >>>> +++ b/include/linux/ima.h >>>> @@ -220,6 +220,17 @@ struct ima_h_table { >>>> struct hlist_head queue[IMA_MEASURE_HTABLE_SIZE]; >>>> }; >>>> >>>> +enum { >>>> + IMAFS_DENTRY_DIR = 0, >>>> + 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; >>>> @@ -266,6 +277,8 @@ struct ima_namespace { >>>> struct mutex ima_write_mutex; >>>> unsigned long ima_fs_flags; >>>> int valid_policy; >>>> + >>>> + struct dentry *dentry[IMAFS_DENTRY_LAST]; >>>> }; >>>> >>>> extern struct ima_namespace init_ima_ns; >>>> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c >>>> index a749a3e79304..3810d11fb463 100644 >>>> --- a/security/integrity/ima/ima_fs.c >>>> +++ b/security/integrity/ima/ima_fs.c >>>> @@ -360,14 +360,6 @@ static ssize_t ima_write_policy(struct file *file, const char __user *buf, >>>> return result; >>>> } >>>> >>>> -static struct dentry *ima_dir; >>>> -static struct dentry *ima_symlink; >>>> -static struct dentry *binary_runtime_measurements; >>>> -static struct dentry *ascii_runtime_measurements; >>>> -static struct dentry *runtime_measurements_count; >>>> -static struct dentry *violations; >>>> -static struct dentry *ima_policy; >>>> - >>>> enum ima_fs_flags { >>>> IMA_FS_BUSY, >>>> }; >>>> @@ -437,8 +429,8 @@ 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; >>>> + securityfs_remove(ns->dentry[IMAFS_DENTRY_IMA_POLICY]); >>>> + ns->dentry[IMAFS_DENTRY_IMA_POLICY] = NULL; >>>> #elif defined(CONFIG_IMA_WRITE_POLICY) >>>> clear_bit(IMA_FS_BUSY, &ns->ima_fs_flags); >>>> #elif defined(CONFIG_IMA_READ_POLICY) >>>> @@ -455,58 +447,72 @@ static const struct file_operations ima_measure_policy_ops = { >>>> .llseek = generic_file_llseek, >>>> }; >>>> >>>> -int __init ima_fs_init(void) >>>> +static void ima_fs_ns_free_dentries(struct ima_namespace *ns) >>>> { >>>> - ima_dir = securityfs_create_dir("ima", integrity_dir); >>>> - if (IS_ERR(ima_dir)) >>>> + int i; >>>> + >>>> + for (i = IMAFS_DENTRY_LAST - 1; i >= 0; i--) >>>> + securityfs_remove(ns->dentry[i]); >>>> + >>>> + memset(ns->dentry, 0, sizeof(ns->dentry)); >>>> +} >>>> + >>>> +static int __init ima_securityfs_init(struct user_namespace *user_ns) >>>> +{ >>>> + struct ima_namespace *ns = user_ns->ima_ns; >>>> + struct dentry *ima_dir; >>>> + >>>> + ns->dentry[IMAFS_DENTRY_DIR] = securityfs_create_dir("ima", integrity_dir); >>>> + if (IS_ERR(ns->dentry[IMAFS_DENTRY_DIR])) >>>> return -1; >>>> + ima_dir = ns->dentry[IMAFS_DENTRY_DIR]; >>>> >>>> - ima_symlink = securityfs_create_symlink("ima", NULL, "integrity/ima", >>>> - NULL); >>>> - if (IS_ERR(ima_symlink)) >>>> + ns->dentry[IMAFS_DENTRY_SYMLINK] = >>>> + securityfs_create_symlink("ima", NULL, "integrity/ima", NULL); >>>> + if (IS_ERR(ns->dentry[IMAFS_DENTRY_SYMLINK])) >>>> goto out; >>>> >>>> - binary_runtime_measurements = >>>> + ns->dentry[IMAFS_DENTRY_BINARY_RUNTIME_MEASUREMENTS] = >>>> securityfs_create_file("binary_runtime_measurements", >>>> S_IRUSR | S_IRGRP, ima_dir, NULL, >>>> &ima_measurements_ops); >>>> - if (IS_ERR(binary_runtime_measurements)) >>>> + if (IS_ERR(ns->dentry[IMAFS_DENTRY_BINARY_RUNTIME_MEASUREMENTS])) >>>> goto out; >>>> >>>> - ascii_runtime_measurements = >>>> + ns->dentry[IMAFS_DENTRY_ASCII_RUNTIME_MEASUREMENTS] = >>>> securityfs_create_file("ascii_runtime_measurements", >>>> S_IRUSR | S_IRGRP, ima_dir, NULL, >>>> &ima_ascii_measurements_ops); >>>> - if (IS_ERR(ascii_runtime_measurements)) >>>> + if (IS_ERR(ns->dentry[IMAFS_DENTRY_ASCII_RUNTIME_MEASUREMENTS])) >>>> goto out; >>>> >>>> - runtime_measurements_count = >>>> + ns->dentry[IMAFS_DENTRY_RUNTIME_MEASUREMENTS_COUNT] = >>>> securityfs_create_file("runtime_measurements_count", >>>> S_IRUSR | S_IRGRP, ima_dir, NULL, >>>> &ima_measurements_count_ops); >>>> - if (IS_ERR(runtime_measurements_count)) >>>> + if (IS_ERR(ns->dentry[IMAFS_DENTRY_RUNTIME_MEASUREMENTS_COUNT])) >>>> goto out; >>>> >>>> - violations = >>>> + ns->dentry[IMAFS_DENTRY_VIOLATIONS] = >>>> securityfs_create_file("violations", S_IRUSR | S_IRGRP, >>>> ima_dir, NULL, &ima_htable_violations_ops); >>>> - if (IS_ERR(violations)) >>>> + if (IS_ERR(ns->dentry[IMAFS_DENTRY_VIOLATIONS])) >>>> goto out; >>>> >>>> - ima_policy = securityfs_create_file("policy", POLICY_FILE_FLAGS, >>>> + ns->dentry[IMAFS_DENTRY_IMA_POLICY] = >>>> + securityfs_create_file("policy", POLICY_FILE_FLAGS, >>>> ima_dir, NULL, >>>> &ima_measure_policy_ops); >>>> - if (IS_ERR(ima_policy)) >>>> + if (IS_ERR(ns->dentry[IMAFS_DENTRY_IMA_POLICY])) >>>> goto out; >>>> >>>> return 0; >>>> out: >>>> - securityfs_remove(violations); >>>> - securityfs_remove(runtime_measurements_count); >>>> - securityfs_remove(ascii_runtime_measurements); >>>> - securityfs_remove(binary_runtime_measurements); >>>> - securityfs_remove(ima_symlink); >>>> - securityfs_remove(ima_dir); >>>> - securityfs_remove(ima_policy); >>>> + ima_fs_ns_free_dentries(ns); >>>> return -1; >>>> } >>>> + >>>> +int __init ima_fs_init(void) >>>> +{ >>>> + return ima_securityfs_init(&init_user_ns); >>>> +} >>>> -- >>>> 2.31.1 >>>> >>>>
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