linux-kernel - [PATCH 5.14 004/162] mm: fix uninitialized use in overcommit_policy

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Date:   Mon, 27 Sep 2021 19:00:50 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Chen Jun <chenjun102@...wei.com>,
        Michal Hocko <mhocko@...e.com>,
        Feng Tang <feng.tang@...el.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Rui Xiang <rui.xiang@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.14 004/162] mm: fix uninitialized use in overcommit_policy_handler

From: Chen Jun <chenjun102@...wei.com>

commit bcbda81020c3ee77e2c098cadf3e84f99ca3de17 upstream.

We get an unexpected value of /proc/sys/vm/overcommit_memory after
running the following program:

  int main()
  {
      int fd = open("/proc/sys/vm/overcommit_memory", 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.

Check whether new_policy has been changed by proc_dointvec_minmax.

Link: https://lkml.kernel.org/r/20210923020524.13289-1-chenjun102@huawei.com
Fixes: 56f3547bfa4d ("mm: adjust vm_committed_as_batch according to vm overcommit policy")
Signed-off-by: Chen Jun <chenjun102@...wei.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Reviewed-by: Feng Tang <feng.tang@...el.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@...wei.com>
Cc: Rui Xiang <rui.xiang@...wei.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/util.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/util.c
+++ b/mm/util.c
@@ -768,7 +768,7 @@ int overcommit_policy_handler(struct ctl
 		size_t *lenp, loff_t *ppos)
 {
 	struct ctl_table t;
-	int new_policy;
+	int new_policy = -1;
 	int ret;
 
 	/*
@@ -786,7 +786,7 @@ int overcommit_policy_handler(struct ctl
 		t = *table;
 		t.data = &new_policy;
 		ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
-		if (ret)
+		if (ret || new_policy == -1)
 			return ret;
 
 		mm_compute_batch(new_policy);