linux-kernel - [PATCH] mm: Fix the uninitialized use in overcommit_policy

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Date:   Tue, 21 Sep 2021 14:03:01 +0000
From:   Chen Jun <chenjun102@...wei.com>
To:     <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
CC:     <akpm@...ux-foundation.org>, <feng.tang@...el.com>,
        <mhocko@...e.com>, <rui.xiang@...wei.com>
Subject: [PATCH] mm: Fix the uninitialized use in overcommit_policy_handler

An unexpected value of /proc/sys/vm/panic_on_oom we will get,
after running the following program

int main()
{
    int fd = open("/proc/sys/vm/panic_on_oom", O_RDWR)
    write(fd, "1", 1);
    write(fd, "2", 1);
    close(fd);
}

write(fd, "2", 1) will pass *ppos = 1 to proc_dointvec_minmax.
proc_dointvec_minmax will return 0 without setting new_policy.

t.data = &new_policy;
ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos)
      -->do_proc_dointvec
         -->__do_proc_dointvec
              if (write) {
                if (proc_first_pos_non_zero_ignore(ppos, table))
                  goto out;

sysctl_overcommit_memory = new_policy;

so sysctl_overcommit_memory will be set to an uninitialized value.

Initialize new_policy with sysctl_overcommit_memory.

Fixes: 56f3547bfa4d ("mm: adjust vm_committed_as_batch according to vm overcommit policy"
Signed-off-by: Chen Jun <chenjun102@...wei.com>
---
 mm/util.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/util.c b/mm/util.c
index 4ddb6e186dd5..b4af8a1de4f7 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -756,7 +756,7 @@ int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
 		size_t *lenp, loff_t *ppos)
 {
 	struct ctl_table t;
-	int new_policy;
+	int new_policy = sysctl_overcommit_memory;
 	int ret;
 
 	/*
-- 
2.17.1