From: Yutian Yang <nglaive@gmail.com> To: mhocko@kernel.org, hannes@cmpxchg.org, vdavydov.dev@gmail.com Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, shenwenbo@zju.edu.cn, Yutian Yang <nglaive@gmail.com> Subject: [PATCH] memcg: charge semaphores and sem_undo objects Date: Thu, 15 Jul 2021 03:14:44 -0400 [thread overview] Message-ID: <1626333284-1404-1-git-send-email-nglaive@gmail.com> (raw) This patch adds accounting flags to semaphores and sem_undo allocation sites so that kernel could correctly charge these objects. A malicious user could take up more than 63GB unaccounted memory under default sysctl settings by exploiting the unaccounted objects. She could allocate up to 32,000 unaccounted semaphore sets with up to 32,000 unaccounted semaphore objects in each set. She could further allocate one sem_undo unaccounted object for each semaphore set. The following code shows a PoC that takes ~63GB unaccounted memory, while it is charged for only less than 1MB memory usage. We evaluate the PoC on QEMU x86_64 v5.2.90 + Linux kernel v5.10.19 + Debian buster. /*------------------------- POC code ----------------------------*/ #define _GNU_SOURCE #include <sys/types.h> #include <sys/ipc.h> #include <sys/sem.h> #include <sys/stat.h> #include <time.h> #include <stdint.h> #include <stdlib.h> #include <unistd.h> #include <stdio.h> #include <sched.h> #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \ } while (0) int main(int argc, char *argv[]) { int err, semid; struct sembuf sops; for (int i = 0; i < 31200; ++i) { semid = semget(IPC_PRIVATE, 31200, IPC_CREAT); if (semid == -1) { errExit("semget"); } sops.sem_num = 0; sops.sem_op = 1; sops.sem_flg = SEM_UNDO; err = semop(semid, &sops, 1); if (err == -1) { errExit("semop"); } } while(1); return 0; } /*-------------------------- end --------------------------------*/ Thanks! Yutian Yang, Zhejiang University Signed-off-by: Yutian Yang <nglaive@gmail.com> --- ipc/sem.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/ipc/sem.c b/ipc/sem.c index f6c30a85d..6860de0b1 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -511,7 +511,7 @@ static struct sem_array *sem_alloc(size_t nsems) if (nsems > (INT_MAX - sizeof(*sma)) / sizeof(sma->sems[0])) return NULL; - sma = kvzalloc(struct_size(sma, sems, nsems), GFP_KERNEL); + sma = kvzalloc(struct_size(sma, sems, nsems), GFP_KERNEL_ACCOUNT); if (unlikely(!sma)) return NULL; @@ -1935,7 +1935,7 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid) rcu_read_unlock(); /* step 2: allocate new undo structure */ - new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL); + new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL_ACCOUNT); if (!new) { ipc_rcu_putref(&sma->sem_perm, sem_rcu_free); return ERR_PTR(-ENOMEM); -- 2.25.1
next reply other threads:[~2021-07-15 7:14 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-07-15 7:14 Yutian Yang [this message] 2021-07-15 17:05 ` Shakeel Butt 2021-07-16 3:57 ` Vasily Averin 2021-07-15 17:49 ` Matthew Wilcox 2021-07-15 18:22 ` Shakeel Butt
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