From: Chen Jun chenjun102@huawei.com Subject: mm: fix uninitialized use in overcommit_policy_handler

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@huawei.com Acked-by: Michal Hocko mhocko@suse.com Reviewed-by: Feng Tang feng.tang@intel.com Reviewed-by: Kefeng Wang wangkefeng.wang@huawei.com Cc: Rui Xiang rui.xiang@huawei.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/util.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/util.c~mm-fix-the-uninitialized-use-in-overcommit_policy_handler +++ a/mm/util.c @@ -787,7 +787,7 @@ 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;

/* @@ -805,7 +805,7 @@ 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); _