From 905ae01c4ae2ae3df05bb141801b1db4b7d83c61 Mon Sep 17 00:00:00 2001 From: Alexey Gladkov Date: Thu, 22 Apr 2021 14:27:09 +0200 Subject: 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 Signed-off-by: Alexey Gladkov Link: https://lkml.kernel.org/r/b37aaef28d8b9b0d757e07ba6dd27281bbe39259.1619094428.git.legion@kernel.org Signed-off-by: Eric W. Biederman --- kernel/cred.c | 40 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+) (limited to 'kernel/cred.c') diff --git a/kernel/cred.c b/kernel/cred.c index 421b1149c651..58a8a9e24347 100644 --- 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; -- cgit v1.2.3 From 21d1c5e386bc751f1953b371d72cd5b7d9c9e270 Mon Sep 17 00:00:00 2001 From: Alexey Gladkov Date: Thu, 22 Apr 2021 14:27:11 +0200 Subject: Reimplement RLIMIT_NPROC on top of ucounts The rlimit counter is tied to uid in the user_namespace. This allows rlimit values to be specified in userns even if they are already globally exceeded by the user. However, the value of the previous user_namespaces cannot be exceeded. To illustrate the impact of rlimits, let's say there is a program that does not fork. Some service-A wants to run this program as user X in multiple containers. Since the program never fork the service wants to set RLIMIT_NPROC=1. service-A \- program (uid=1000, container1, rlimit_nproc=1) \- program (uid=1000, container2, rlimit_nproc=1) The service-A sets RLIMIT_NPROC=1 and runs the program in container1. When the service-A tries to run a program with RLIMIT_NPROC=1 in container2 it fails since user X already has one running process. We cannot use existing inc_ucounts / dec_ucounts because they do not allow us to exceed the maximum for the counter. Some rlimits can be overlimited by root or if the user has the appropriate capability. Changelog v11: * Change inc_rlimit_ucounts() which now returns top value of ucounts. * Drop inc_rlimit_ucounts_and_test() because the return code of inc_rlimit_ucounts() can be checked. Signed-off-by: Alexey Gladkov Link: https://lkml.kernel.org/r/c5286a8aa16d2d698c222f7532f3d735c82bc6bc.1619094428.git.legion@kernel.org Signed-off-by: Eric W. Biederman --- kernel/cred.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) (limited to 'kernel/cred.c') diff --git a/kernel/cred.c b/kernel/cred.c index 58a8a9e24347..dcfa30b337c5 100644 --- a/kernel/cred.c +++ b/kernel/cred.c @@ -360,7 +360,7 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags) kdebug("share_creds(%p{%d,%d})", p->cred, atomic_read(&p->cred->usage), read_cred_subscribers(p->cred)); - atomic_inc(&p->cred->user->processes); + inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); return 0; } @@ -395,8 +395,8 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags) } #endif - atomic_inc(&new->user->processes); p->cred = p->real_cred = get_cred(new); + inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); alter_cred_subscribers(new, 2); validate_creds(new); return 0; @@ -496,12 +496,12 @@ int commit_creds(struct cred *new) * in set_user(). */ alter_cred_subscribers(new, 2); - if (new->user != old->user) - atomic_inc(&new->user->processes); + if (new->user != old->user || new->user_ns != old->user_ns) + inc_rlimit_ucounts(new->ucounts, UCOUNT_RLIMIT_NPROC, 1); rcu_assign_pointer(task->real_cred, new); rcu_assign_pointer(task->cred, new); if (new->user != old->user) - atomic_dec(&old->user->processes); + dec_rlimit_ucounts(old->ucounts, UCOUNT_RLIMIT_NPROC, 1); alter_cred_subscribers(old, -2); /* send notifications */ -- cgit v1.2.3 From 5e6b8a50a7cec5686ee2c4bda1d49899c79a7eae Mon Sep 17 00:00:00 2001 From: Yang Yingliang Date: Wed, 26 May 2021 22:38:05 +0800 Subject: cred: add missing return error code when set_cred_ucounts() failed If set_cred_ucounts() failed, we need return the error code. Fixes: 905ae01c4ae2 ("Add a reference to ucounts for each cred") Reported-by: Hulk Robot Signed-off-by: Yang Yingliang Link: https://lkml.kernel.org/r/20210526143805.2549649-1-yangyingliang@huawei.com Reviewed-by: Alexey Gladkov Signed-off-by: Eric W. Biederman --- kernel/cred.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'kernel/cred.c') diff --git a/kernel/cred.c b/kernel/cred.c index dcfa30b337c5..5a1d9702658e 100644 --- a/kernel/cred.c +++ b/kernel/cred.c @@ -372,7 +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) + ret = set_cred_ucounts(new); + if (ret < 0) goto error_put; } -- cgit v1.2.3