From: Muchun Song songmuchun@bytedance.com
mainline inclusion from mainline-v5.9-rc4 commit 17743798d81238ab13050e8e2833699b54e15467 category: bugfix bugzilla: NA CVE: CVE-2020-25285
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There is a race between the assignment of `table->data` and write value to the pointer of `table->data` in the __do_proc_doulongvec_minmax() on the other thread.
CPU0: CPU1: proc_sys_write hugetlb_sysctl_handler proc_sys_call_handler hugetlb_sysctl_handler_common hugetlb_sysctl_handler table->data = &tmp; hugetlb_sysctl_handler_common table->data = &tmp; proc_doulongvec_minmax do_proc_doulongvec_minmax sysctl_head_finish __do_proc_doulongvec_minmax unuse_table i = table->data; *i = val; // corrupt CPU1's stack
Fix this by duplicating the `table`, and only update the duplicate of it. And introduce a helper of proc_hugetlb_doulongvec_minmax() to simplify the code.
The following oops was seen:
BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor instruction fetch in kernel mode #PF: error_code(0x0010) - not-present page Code: Bad RIP value. ... Call Trace: ? set_max_huge_pages+0x3da/0x4f0 ? alloc_pool_huge_page+0x150/0x150 ? proc_doulongvec_minmax+0x46/0x60 ? hugetlb_sysctl_handler_common+0x1c7/0x200 ? nr_hugepages_store+0x20/0x20 ? copy_fd_bitmaps+0x170/0x170 ? hugetlb_sysctl_handler+0x1e/0x20 ? proc_sys_call_handler+0x2f1/0x300 ? unregister_sysctl_table+0xb0/0xb0 ? __fd_install+0x78/0x100 ? proc_sys_write+0x14/0x20 ? __vfs_write+0x4d/0x90 ? vfs_write+0xef/0x240 ? ksys_write+0xc0/0x160 ? __ia32_sys_read+0x50/0x50 ? __close_fd+0x129/0x150 ? __x64_sys_write+0x43/0x50 ? do_syscall_64+0x6c/0x200 ? entry_SYSCALL_64_after_hwframe+0x44/0xa9
Fixes: e5ff215941d5 ("hugetlb: multiple hstates for multiple page sizes") Signed-off-by: Muchun Song songmuchun@bytedance.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Reviewed-by: Mike Kravetz mike.kravetz@oracle.com Cc: Andi Kleen ak@linux.intel.com Link: http://lkml.kernel.org/r/20200828031146.43035-1-songmuchun@bytedance.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Yang Yingliang yangyingliang@huawei.com Reviewed-by: Jason Yan yanaijie@huawei.com Reviewed-by: Kefeng Wang wangkefeng.wang@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- mm/hugetlb.c | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 5356f7e5daf2..efb68abe9f35 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3045,6 +3045,22 @@ static unsigned int cpuset_mems_nr(unsigned int *array) }
#ifdef CONFIG_SYSCTL +static int proc_hugetlb_doulongvec_minmax(struct ctl_table *table, int write, + void *buffer, size_t *length, + loff_t *ppos, unsigned long *out) +{ + struct ctl_table dup_table; + + /* + * In order to avoid races with __do_proc_doulongvec_minmax(), we + * can duplicate the @table and alter the duplicate of it. + */ + dup_table = *table; + dup_table.data = out; + + return proc_doulongvec_minmax(&dup_table, write, buffer, length, ppos); +} + static int hugetlb_sysctl_handler_common(bool obey_mempolicy, struct ctl_table *table, int write, void __user *buffer, size_t *length, loff_t *ppos) @@ -3056,9 +3072,8 @@ static int hugetlb_sysctl_handler_common(bool obey_mempolicy, if (!hugepages_supported()) return -EOPNOTSUPP;
- table->data = &tmp; - table->maxlen = sizeof(unsigned long); - ret = proc_doulongvec_minmax(table, write, buffer, length, ppos); + ret = proc_hugetlb_doulongvec_minmax(table, write, buffer, length, ppos, + &tmp); if (ret) goto out;
@@ -3115,9 +3130,8 @@ int hugetlb_overcommit_handler(struct ctl_table *table, int write, if (write && hstate_is_gigantic(h)) return -EINVAL;
- table->data = &tmp; - table->maxlen = sizeof(unsigned long); - ret = proc_doulongvec_minmax(table, write, buffer, length, ppos); + ret = proc_hugetlb_doulongvec_minmax(table, write, buffer, length, ppos, + &tmp); if (ret) goto out;