Add a reference to ucounts for each cred

For RLIMIT_NPROC and some other rlimits the user_struct that holds the
global limit is kept alive for the lifetime of a process by keeping it
in struct cred. Adding a pointer to ucounts in the struct cred will
allow to track RLIMIT_NPROC not only for user in the system, but for
user in the user_namespace.

Updating ucounts may require memory allocation which may fail. So, we
cannot change cred.ucounts in the commit_creds() because this function
cannot fail and it should always return 0. For this reason, we modify
cred.ucounts before calling the commit_creds().

Changelog

v6:
* Fix null-ptr-deref in is_ucounts_overlimit() detected by trinity. This
  error was caused by the fact that cred_alloc_blank() left the ucounts
  pointer empty.

Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Alexey Gladkov <legion@kernel.org>
Link: https://lkml.kernel.org/r/b37aaef28d8b9b0d757e07ba6dd27281bbe39259.1619094428.git.legion@kernel.org
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

diff --git a/fs/exec.c b/fs/exec.c
index 18594f11c31fe12e28e80349e7fb1211613e681c..d7c4187ca023e2e96b4295574efb8ec528b678f1 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1360,6 +1360,10 @@ int begin_new_exec(struct linux_binprm * bprm)
        WRITE_ONCE(me->self_exec_id, me->self_exec_id + 1);
        flush_signal_handlers(me, 0);
 
+       retval = set_cred_ucounts(bprm->cred);
+       if (retval < 0)
+               goto out_unlock;
+
        /*
         * install the new credentials for this executable
         */

diff --git a/include/linux/cred.h b/include/linux/cred.h
index 4c6350503697779149782c170289d9cd2f7a778b..66436e655032854babefaee943f4510743b19966 100644 (file)
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -144,6 +144,7 @@ struct cred {
 #endif
        struct user_struct *user;       /* real user ID subscription */
        struct user_namespace *user_ns; /* user_ns the caps and keyrings are relative to. */
+       struct ucounts *ucounts;
        struct group_info *group_info;  /* supplementary groups for euid/fsgid */
        /* RCU deletion */
        union {
@@ -170,6 +171,7 @@ extern int set_security_override_from_ctx(struct cred *, const char *);
 extern int set_create_files_as(struct cred *, struct inode *);
 extern int cred_fscmp(const struct cred *, const struct cred *);
 extern void __init cred_init(void);
+extern int set_cred_ucounts(struct cred *);
 
 /*
  * check for validity of credentials

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index c242c10906c502285c9e4426cbc41064498205ac..7919b80d57ed09fecae76f29e1de4fbd2fa524f3 100644 (file)
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -100,11 +100,15 @@ struct ucounts {
 };
 
 extern struct user_namespace init_user_ns;
+extern struct ucounts init_ucounts;
 
 bool setup_userns_sysctls(struct user_namespace *ns);
 void retire_userns_sysctls(struct user_namespace *ns);
 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, enum ucount_type type);
 void dec_ucount(struct ucounts *ucounts, enum ucount_type type);
+struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid);
+struct ucounts *get_ucounts(struct ucounts *ucounts);
+void put_ucounts(struct ucounts *ucounts);
 
 #ifdef CONFIG_USER_NS
 

diff --git a/kernel/cred.c b/kernel/cred.c
index 421b1149c6516004221159824dc6c18770db64e6..58a8a9e24347d4202a96a412e17ce2288db5c273 100644 (file)
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -60,6 +60,7 @@ struct cred init_cred = {
        .user                   = INIT_USER,
        .user_ns                = &init_user_ns,
        .group_info             = &init_groups,
+       .ucounts                = &init_ucounts,
 };
 
 static inline void set_cred_subscribers(struct cred *cred, int n)
@@ -119,6 +120,8 @@ static void put_cred_rcu(struct rcu_head *rcu)
        if (cred->group_info)
                put_group_info(cred->group_info);
        free_uid(cred->user);
+       if (cred->ucounts)
+               put_ucounts(cred->ucounts);
        put_user_ns(cred->user_ns);
        kmem_cache_free(cred_jar, cred);
 }
@@ -222,6 +225,7 @@ struct cred *cred_alloc_blank(void)
 #ifdef CONFIG_DEBUG_CREDENTIALS
        new->magic = CRED_MAGIC;
 #endif
+       new->ucounts = get_ucounts(&init_ucounts);
 
        if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)
                goto error;
@@ -284,6 +288,11 @@ struct cred *prepare_creds(void)
 
        if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
                goto error;
+
+       new->ucounts = get_ucounts(new->ucounts);
+       if (!new->ucounts)
+               goto error;
+
        validate_creds(new);
        return new;
 
@@ -363,6 +372,8 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
                ret = create_user_ns(new);
                if (ret < 0)
                        goto error_put;
+               if (set_cred_ucounts(new) < 0)
+                       goto error_put;
        }
 
 #ifdef CONFIG_KEYS
@@ -653,6 +664,31 @@ int cred_fscmp(const struct cred *a, const struct cred *b)
 }
 EXPORT_SYMBOL(cred_fscmp);
 
+int set_cred_ucounts(struct cred *new)
+{
+       struct task_struct *task = current;
+       const struct cred *old = task->real_cred;
+       struct ucounts *old_ucounts = new->ucounts;
+
+       if (new->user == old->user && new->user_ns == old->user_ns)
+               return 0;
+
+       /*
+        * This optimization is needed because alloc_ucounts() uses locks
+        * for table lookups.
+        */
+       if (old_ucounts && old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->euid))
+               return 0;
+
+       if (!(new->ucounts = alloc_ucounts(new->user_ns, new->euid)))
+               return -EAGAIN;
+
+       if (old_ucounts)
+               put_ucounts(old_ucounts);
+
+       return 0;
+}
+
 /*
  * initialise the credentials stuff
  */
@@ -719,6 +755,10 @@ struct cred *prepare_kernel_cred(struct task_struct *daemon)
        if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
                goto error;
 
+       new->ucounts = get_ucounts(new->ucounts);
+       if (!new->ucounts)
+               goto error;
+
        put_cred(old);
        validate_creds(new);
        return new;

diff --git a/kernel/fork.c b/kernel/fork.c
index 426cd0c51f9ebb7d903d14c7e220a018ac38e27b..321a5e31d817e17a266ea36ab60614436913af0a 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2995,6 +2995,12 @@ int ksys_unshare(unsigned long unshare_flags)
        if (err)
                goto bad_unshare_cleanup_cred;
 
+       if (new_cred) {
+               err = set_cred_ucounts(new_cred);
+               if (err)
+                       goto bad_unshare_cleanup_cred;
+       }
+
        if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
                if (do_sysvsem) {
                        /*

diff --git a/kernel/sys.c b/kernel/sys.c
index 2e2e3f378d97f61625c6a936b38e6c86c7037e0d..cabfc5b861754887fdc44222e3465898e2e3b4ea 100644 (file)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -552,6 +552,10 @@ long __sys_setreuid(uid_t ruid, uid_t euid)
        if (retval < 0)
                goto error;
 
+       retval = set_cred_ucounts(new);
+       if (retval < 0)
+               goto error;
+
        return commit_creds(new);
 
 error:
@@ -610,6 +614,10 @@ long __sys_setuid(uid_t uid)
        if (retval < 0)
                goto error;
 
+       retval = set_cred_ucounts(new);
+       if (retval < 0)
+               goto error;
+
        return commit_creds(new);
 
 error:
@@ -685,6 +693,10 @@ long __sys_setresuid(uid_t ruid, uid_t euid, uid_t suid)
        if (retval < 0)
                goto error;
 
+       retval = set_cred_ucounts(new);
+       if (retval < 0)
+               goto error;
+
        return commit_creds(new);
 
 error:

diff --git a/kernel/ucount.c b/kernel/ucount.c
index 04c561751af1e8a92f6a62e331c3f6b68fd1f0d1..50cc1dfb7d28aa556f992dd4b09c5570fdd33b0a 100644 (file)
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -8,6 +8,12 @@
 #include <linux/kmemleak.h>
 #include <linux/user_namespace.h>
 
+struct ucounts init_ucounts = {
+       .ns    = &init_user_ns,
+       .uid   = GLOBAL_ROOT_UID,
+       .count = 1,
+};
+
 #define UCOUNTS_HASHTABLE_BITS 10
 static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
 static DEFINE_SPINLOCK(ucounts_lock);
@@ -125,7 +131,15 @@ static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struc
        return NULL;
 }
 
-static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
+static void hlist_add_ucounts(struct ucounts *ucounts)
+{
+       struct hlist_head *hashent = ucounts_hashentry(ucounts->ns, ucounts->uid);
+       spin_lock_irq(&ucounts_lock);
+       hlist_add_head(&ucounts->node, hashent);
+       spin_unlock_irq(&ucounts_lock);
+}
+
+struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
 {
        struct hlist_head *hashent = ucounts_hashentry(ns, uid);
        struct ucounts *ucounts, *new;
@@ -160,7 +174,26 @@ static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
        return ucounts;
 }
 
-static void put_ucounts(struct ucounts *ucounts)
+struct ucounts *get_ucounts(struct ucounts *ucounts)
+{
+       unsigned long flags;
+
+       if (!ucounts)
+               return NULL;
+
+       spin_lock_irqsave(&ucounts_lock, flags);
+       if (ucounts->count == INT_MAX) {
+               WARN_ONCE(1, "ucounts: counter has reached its maximum value");
+               ucounts = NULL;
+       } else {
+               ucounts->count += 1;
+       }
+       spin_unlock_irqrestore(&ucounts_lock, flags);
+
+       return ucounts;
+}
+
+void put_ucounts(struct ucounts *ucounts)
 {
        unsigned long flags;
 
@@ -194,7 +227,7 @@ struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
 {
        struct ucounts *ucounts, *iter, *bad;
        struct user_namespace *tns;
-       ucounts = get_ucounts(ns, uid);
+       ucounts = alloc_ucounts(ns, uid);
        for (iter = ucounts; iter; iter = tns->ucounts) {
                long max;
                tns = iter->ns;
@@ -237,6 +270,7 @@ static __init int user_namespace_sysctl_init(void)
        BUG_ON(!user_header);
        BUG_ON(!setup_userns_sysctls(&init_user_ns));
 #endif
+       hlist_add_ucounts(&init_ucounts);
        return 0;
 }
 subsys_initcall(user_namespace_sysctl_init);

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 9a4b980d695b8f2f525c92a4b3ef058150448d7c..f1b7b4b8ffa256f6912494a3f26c6b1c3b82c249 100644 (file)
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -1340,6 +1340,9 @@ static int userns_install(struct nsset *nsset, struct ns_common *ns)
        put_user_ns(cred->user_ns);
        set_cred_user_ns(cred, get_user_ns(user_ns));
 
+       if (set_cred_ucounts(cred) < 0)
+               return -EINVAL;
+
        return 0;
 }