[PATCH v7 6/7] Reimplement RLIMIT_MEMLOCK on top of ucounts

From: Alexey Gladkov
Date: Tue Feb 16 2021 - 06:15:25 EST

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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.

Changelog

v7:
* Fix hugetlb_file_setup() declaration if CONFIG_HUGETLBFS=n. A `const'
was missing from one of the arguments.

v6:
* Fix bug in hugetlb_file_setup() detected by trinity.

Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Signed-off-by: Alexey Gladkov <gladkov.alexey@xxxxxxxxx>
---
fs/hugetlbfs/inode.c | 16 ++++++++--------
include/linux/hugetlb.h | 4 ++--
include/linux/mm.h | 4 ++--
include/linux/sched/user.h | 1 -
include/linux/shmem_fs.h | 2 +-
include/linux/user_namespace.h | 1 +
ipc/shm.c | 30 +++++++++++++++--------------
kernel/fork.c | 1 +
kernel/ucount.c | 1 +
kernel/user.c | 1 -
kernel/user_namespace.c | 1 +
mm/memfd.c | 5 ++---
mm/mlock.c | 35 +++++++++++++---------------------
mm/mmap.c | 4 ++--
mm/shmem.c | 8 ++++----
15 files changed, 54 insertions(+), 60 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 21c20fd5f9ee..a8757e39cefa 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -1452,7 +1452,7 @@ static int get_hstate_idx(int page_size_log)
* otherwise hugetlb_reserve_pages reserves one less hugepages than intended.
*/
struct file *hugetlb_file_setup(const char *name, size_t size,
- vm_flags_t acctflag, struct user_struct **user,
+ vm_flags_t acctflag, const struct cred **cred,
int creat_flags, int page_size_log)
{
struct inode *inode;
@@ -1464,20 +1464,20 @@ struct file *hugetlb_file_setup(const char *name, size_t size,
if (hstate_idx < 0)
return ERR_PTR(-ENODEV);

- *user = NULL;
+ *cred = NULL;
mnt = hugetlbfs_vfsmount[hstate_idx];
if (!mnt)
return ERR_PTR(-ENOENT);

if (creat_flags == HUGETLB_SHMFS_INODE && !can_do_hugetlb_shm()) {
- *user = current_user();
- if (user_shm_lock(size, *user)) {
+ *cred = current_cred();
+ if (user_shm_lock(size, *cred)) {
task_lock(current);
pr_warn_once("%s (%d): Using mlock ulimits for SHM_HUGETLB is deprecated\n",
current->comm, current->pid);
task_unlock(current);
} else {
- *user = NULL;
+ *cred = NULL;
return ERR_PTR(-EPERM);
}
}
@@ -1504,9 +1504,9 @@ struct file *hugetlb_file_setup(const char *name, size_t size,

iput(inode);
out:
- if (*user) {
- user_shm_unlock(size, *user);
- *user = NULL;
+ if (*cred) {
+ user_shm_unlock(size, *cred);
+ *cred = NULL;
}
return file;
}
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index b5807f23caf8..0a19897b773b 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -434,7 +434,7 @@ static inline struct hugetlbfs_inode_info *HUGETLBFS_I(struct inode *inode)
extern const struct file_operations hugetlbfs_file_operations;
extern const struct vm_operations_struct hugetlb_vm_ops;
struct file *hugetlb_file_setup(const char *name, size_t size, vm_flags_t acct,
- struct user_struct **user, int creat_flags,
+ const struct cred **cred, int creat_flags,
int page_size_log);

static inline bool is_file_hugepages(struct file *file)
@@ -454,7 +454,7 @@ static inline struct hstate *hstate_inode(struct inode *i)
#define is_file_hugepages(file) false
static inline struct file *
hugetlb_file_setup(const char *name, size_t size, vm_flags_t acctflag,
- struct user_struct **user, int creat_flags,
+ const struct cred **cred, int creat_flags,
int page_size_log)
{
return ERR_PTR(-ENOSYS);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ecdf8a8cd6ae..30a37aef1ab9 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1628,8 +1628,8 @@ extern bool can_do_mlock(void);
#else
static inline bool can_do_mlock(void) { return false; }
#endif
-extern int user_shm_lock(size_t, struct user_struct *);
-extern void user_shm_unlock(size_t, struct user_struct *);
+extern int user_shm_lock(size_t, const struct cred *);
+extern void user_shm_unlock(size_t, const struct cred *);

/*
* Parameter block passed down to zap_pte_range in exceptional cases.
diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index 8ba9cec4fb99..82bd2532da6b 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -18,7 +18,6 @@ struct user_struct {
#ifdef CONFIG_EPOLL
atomic_long_t epoll_watches; /* The number of file descriptors currently watched */
#endif
- unsigned long locked_shm; /* How many pages of mlocked shm ? */
unsigned long unix_inflight; /* How many files in flight in unix sockets */
atomic_long_t pipe_bufs; /* how many pages are allocated in pipe buffers */

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index d82b6f396588..10f50b1c4e0e 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -65,7 +65,7 @@ extern struct file *shmem_file_setup_with_mnt(struct vfsmount *mnt,
extern int shmem_zero_setup(struct vm_area_struct *);
extern unsigned long shmem_get_unmapped_area(struct file *, unsigned long addr,
unsigned long len, unsigned long pgoff, unsigned long flags);
-extern int shmem_lock(struct file *file, int lock, struct user_struct *user);
+extern int shmem_lock(struct file *file, int lock, const struct cred *cred);
#ifdef CONFIG_SHMEM
extern const struct address_space_operations shmem_aops;
static inline bool shmem_mapping(struct address_space *mapping)
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index f84b68832c56..966b0d733bb8 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -53,6 +53,7 @@ enum ucount_type {
UCOUNT_RLIMIT_NPROC,
UCOUNT_RLIMIT_MSGQUEUE,
UCOUNT_RLIMIT_SIGPENDING,
+ UCOUNT_RLIMIT_MEMLOCK,
UCOUNT_COUNTS,
};

diff --git a/ipc/shm.c b/ipc/shm.c
index febd88daba8c..9b3fbf33a7b7 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -60,7 +60,7 @@ struct shmid_kernel /* private to the kernel */
time64_t shm_ctim;
struct pid *shm_cprid;
struct pid *shm_lprid;
- struct user_struct *mlock_user;
+ const struct cred *mlock_cred;

/* The task created the shm object. NULL if the task is dead. */
struct task_struct *shm_creator;
@@ -286,10 +286,10 @@ static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
shm_rmid(ns, shp);
shm_unlock(shp);
if (!is_file_hugepages(shm_file))
- shmem_lock(shm_file, 0, shp->mlock_user);
- else if (shp->mlock_user)
+ shmem_lock(shm_file, 0, shp->mlock_cred);
+ else if (shp->mlock_cred)
user_shm_unlock(i_size_read(file_inode(shm_file)),
- shp->mlock_user);
+ shp->mlock_cred);
fput(shm_file);
ipc_update_pid(&shp->shm_cprid, NULL);
ipc_update_pid(&shp->shm_lprid, NULL);
@@ -625,7 +625,7 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)

shp->shm_perm.key = key;
shp->shm_perm.mode = (shmflg & S_IRWXUGO);
- shp->mlock_user = NULL;
+ shp->mlock_cred = NULL;

shp->shm_perm.security = NULL;
error = security_shm_alloc(&shp->shm_perm);
@@ -650,7 +650,7 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
if (shmflg & SHM_NORESERVE)
acctflag = VM_NORESERVE;
file = hugetlb_file_setup(name, hugesize, acctflag,
- &shp->mlock_user, HUGETLB_SHMFS_INODE,
+ &shp->mlock_cred, HUGETLB_SHMFS_INODE,
(shmflg >> SHM_HUGE_SHIFT) & SHM_HUGE_MASK);
} else {
/*
@@ -663,8 +663,10 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
file = shmem_kernel_file_setup(name, size, acctflag);
}
error = PTR_ERR(file);
- if (IS_ERR(file))
+ if (IS_ERR(file)) {
+ shp->mlock_cred = NULL;
goto no_file;
+ }

shp->shm_cprid = get_pid(task_tgid(current));
shp->shm_lprid = NULL;
@@ -698,8 +700,8 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
no_id:
ipc_update_pid(&shp->shm_cprid, NULL);
ipc_update_pid(&shp->shm_lprid, NULL);
- if (is_file_hugepages(file) && shp->mlock_user)
- user_shm_unlock(size, shp->mlock_user);
+ if (is_file_hugepages(file) && shp->mlock_cred)
+ user_shm_unlock(size, shp->mlock_cred);
fput(file);
ipc_rcu_putref(&shp->shm_perm, shm_rcu_free);
return error;
@@ -1105,12 +1107,12 @@ static int shmctl_do_lock(struct ipc_namespace *ns, int shmid, int cmd)
goto out_unlock0;

if (cmd == SHM_LOCK) {
- struct user_struct *user = current_user();
+ const struct cred *cred = current_cred();

- err = shmem_lock(shm_file, 1, user);
+ err = shmem_lock(shm_file, 1, cred);
if (!err && !(shp->shm_perm.mode & SHM_LOCKED)) {
shp->shm_perm.mode |= SHM_LOCKED;
- shp->mlock_user = user;
+ shp->mlock_cred = cred;
}
goto out_unlock0;
}
@@ -1118,9 +1120,9 @@ static int shmctl_do_lock(struct ipc_namespace *ns, int shmid, int cmd)
/* SHM_UNLOCK */
if (!(shp->shm_perm.mode & SHM_LOCKED))
goto out_unlock0;
- shmem_lock(shm_file, 0, shp->mlock_user);
+ shmem_lock(shm_file, 0, shp->mlock_cred);
shp->shm_perm.mode &= ~SHM_LOCKED;
- shp->mlock_user = NULL;
+ shp->mlock_cred = NULL;
get_file(shm_file);
ipc_unlock_object(&shp->shm_perm);
rcu_read_unlock();
diff --git a/kernel/fork.c b/kernel/fork.c
index 99b10b9fe4b6..76ccb000856c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -825,6 +825,7 @@ void __init fork_init(void)
init_user_ns.ucount_max[UCOUNT_RLIMIT_NPROC] = task_rlimit(&init_task, RLIMIT_NPROC);
init_user_ns.ucount_max[UCOUNT_RLIMIT_MSGQUEUE] = task_rlimit(&init_task, RLIMIT_MSGQUEUE);
init_user_ns.ucount_max[UCOUNT_RLIMIT_SIGPENDING] = task_rlimit(&init_task, RLIMIT_SIGPENDING);
+ init_user_ns.ucount_max[UCOUNT_RLIMIT_MEMLOCK] = task_rlimit(&init_task, RLIMIT_MEMLOCK);

#ifdef CONFIG_VMAP_STACK
cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 2ac969fba668..b6242b77eb89 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -84,6 +84,7 @@ static struct ctl_table user_table[] = {
{ },
{ },
{ },
+ { },
{ }
};
#endif /* CONFIG_SYSCTL */
diff --git a/kernel/user.c b/kernel/user.c
index 6737327f83be..c82399c1618a 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -98,7 +98,6 @@ static DEFINE_SPINLOCK(uidhash_lock);
/* root_user.__count is 1, for init task cred */
struct user_struct root_user = {
.__count = REFCOUNT_INIT(1),
- .locked_shm = 0,
.uid = GLOBAL_ROOT_UID,
.ratelimit = RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
};
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index df1bed32dd48..5ef0d4b182ba 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -124,6 +124,7 @@ int create_user_ns(struct cred *new)
ns->ucount_max[UCOUNT_RLIMIT_NPROC] = rlimit(RLIMIT_NPROC);
ns->ucount_max[UCOUNT_RLIMIT_MSGQUEUE] = rlimit(RLIMIT_MSGQUEUE);
ns->ucount_max[UCOUNT_RLIMIT_SIGPENDING] = rlimit(RLIMIT_SIGPENDING);
+ ns->ucount_max[UCOUNT_RLIMIT_MEMLOCK] = rlimit(RLIMIT_MEMLOCK);
ns->ucounts = ucounts;

/* Inherit USERNS_SETGROUPS_ALLOWED from our parent */
diff --git a/mm/memfd.c b/mm/memfd.c
index 2647c898990c..473515a74b99 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -297,9 +297,8 @@ SYSCALL_DEFINE2(memfd_create,
}

if (flags & MFD_HUGETLB) {
- struct user_struct *user = NULL;
-
- file = hugetlb_file_setup(name, 0, VM_NORESERVE, &user,
+ const struct cred *cred;
+ file = hugetlb_file_setup(name, 0, VM_NORESERVE, &cred,
HUGETLB_ANONHUGE_INODE,
(flags >> MFD_HUGE_SHIFT) &
MFD_HUGE_MASK);
diff --git a/mm/mlock.c b/mm/mlock.c
index 55b3b3672977..2d49d1afd7e0 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -812,15 +812,10 @@ SYSCALL_DEFINE0(munlockall)
return ret;
}

-/*
- * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
- * shm segments) get accounted against the user_struct instead.
- */
-static DEFINE_SPINLOCK(shmlock_user_lock);
-
-int user_shm_lock(size_t size, struct user_struct *user)
+int user_shm_lock(size_t size, const struct cred *cred)
{
unsigned long lock_limit, locked;
+ bool overlimit;
int allowed = 0;

locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
@@ -828,22 +823,18 @@ int user_shm_lock(size_t size, struct user_struct *user)
if (lock_limit == RLIM_INFINITY)
allowed = 1;
lock_limit >>= PAGE_SHIFT;
- spin_lock(&shmlock_user_lock);
- if (!allowed &&
- locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
- goto out;
- get_uid(user);
- user->locked_shm += locked;
- allowed = 1;
-out:
- spin_unlock(&shmlock_user_lock);
- return allowed;
+
+ overlimit = inc_rlimit_ucounts_and_test(cred->ucounts, UCOUNT_RLIMIT_MEMLOCK,
+ locked, lock_limit);
+
+ if (!allowed && overlimit && !capable(CAP_IPC_LOCK)) {
+ dec_rlimit_ucounts(cred->ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
+ return 0;
+ }
+ return 1;
}

-void user_shm_unlock(size_t size, struct user_struct *user)
+void user_shm_unlock(size_t size, const struct cred *cred)
{
- spin_lock(&shmlock_user_lock);
- user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
- spin_unlock(&shmlock_user_lock);
- free_uid(user);
+ dec_rlimit_ucounts(cred->ucounts, UCOUNT_RLIMIT_MEMLOCK, (size + PAGE_SIZE - 1) >> PAGE_SHIFT);
}
diff --git a/mm/mmap.c b/mm/mmap.c
index dc7206032387..76edf28344a4 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1607,7 +1607,7 @@ unsigned long ksys_mmap_pgoff(unsigned long addr, unsigned long len,
goto out_fput;
}
} else if (flags & MAP_HUGETLB) {
- struct user_struct *user = NULL;
+ const struct cred *cred;
struct hstate *hs;

hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
@@ -1623,7 +1623,7 @@ unsigned long ksys_mmap_pgoff(unsigned long addr, unsigned long len,
*/
file = hugetlb_file_setup(HUGETLB_ANON_FILE, len,
VM_NORESERVE,
- &user, HUGETLB_ANONHUGE_INODE,
+ &cred, HUGETLB_ANONHUGE_INODE,
(flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
if (IS_ERR(file))
return PTR_ERR(file);
diff --git a/mm/shmem.c b/mm/shmem.c
index 7c6b6d8f6c39..de9bf6866f51 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2225,7 +2225,7 @@ static struct mempolicy *shmem_get_policy(struct vm_area_struct *vma,
}
#endif

-int shmem_lock(struct file *file, int lock, struct user_struct *user)
+int shmem_lock(struct file *file, int lock, const struct cred *cred)
{
struct inode *inode = file_inode(file);
struct shmem_inode_info *info = SHMEM_I(inode);
@@ -2237,13 +2237,13 @@ int shmem_lock(struct file *file, int lock, struct user_struct *user)
* no serialization needed when called from shm_destroy().
*/
if (lock && !(info->flags & VM_LOCKED)) {
- if (!user_shm_lock(inode->i_size, user))
+ if (!user_shm_lock(inode->i_size, cred))
goto out_nomem;
info->flags |= VM_LOCKED;
mapping_set_unevictable(file->f_mapping);
}
- if (!lock && (info->flags & VM_LOCKED) && user) {
- user_shm_unlock(inode->i_size, user);
+ if (!lock && (info->flags & VM_LOCKED) && cred) {
+ user_shm_unlock(inode->i_size, cred);
info->flags &= ~VM_LOCKED;
mapping_clear_unevictable(file->f_mapping);
}
--
2.29.2

Next message: Jiri Olsa: "Re: [PATCH v6 2/3] perf tools: Add lexical definition of event name"
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