+ mm-memcontrol-fix-out-of-bounds-on-the-buf-returned-by-memory_stat_format.patch added to -mm tree

+ mm-memcontrol-fix-out-of-bounds-on-the-buf-returned-by-memory_stat_format.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm: memcontrol: fix out-of-bounds on the buf returned by memory_stat_format
has been added to the -mm tree.  Its filename is
     mm-memcontrol-fix-out-of-bounds-on-the-buf-returned-by-memory_stat_format.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-memcontrol-fix-out-of-bounds-on-the-buf-returned-by-memory_stat_format.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-memcontrol-fix-out-of-bounds-on-the-buf-returned-by-memory_stat_format.patch

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------------------------------------------------------
From: Muchun Song <songmuchun@bytedance.com>
Subject: mm: memcontrol: fix out-of-bounds on the buf returned by memory_stat_format

The memory_stat_format() returns a format string, but the return buf may
not including the trailing '\0', so the users may read the buf out of
bounds.

Link: https://lkml.kernel.org/r/20200912155100.25578-1-songmuchun@bytedance.com
Fixes: c8713d0b2312 ("mm: memcontrol: dump memory.stat during cgroup OOM")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

--- a/mm/memcontrol.c~mm-memcontrol-fix-out-of-bounds-on-the-buf-returned-by-memory_stat_format
+++ a/mm/memcontrol.c
@@ -1456,12 +1456,13 @@ static bool mem_cgroup_wait_acct_move(st
 	return false;
 }
 
-static char *memory_stat_format(struct mem_cgroup *memcg)
+static const char *memory_stat_format(struct mem_cgroup *memcg)
 {
 	struct seq_buf s;
 	int i;
 
-	seq_buf_init(&s, kmalloc(PAGE_SIZE, GFP_KERNEL), PAGE_SIZE);
+	/* Reserve a byte for the trailing null */
+	seq_buf_init(&s, kmalloc(PAGE_SIZE, GFP_KERNEL), PAGE_SIZE - 1);
 	if (!s.buffer)
 		return NULL;
 
@@ -1570,7 +1571,8 @@ static char *memory_stat_format(struct m
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
 	/* The above should easily fit into one page */
-	WARN_ON_ONCE(seq_buf_has_overflowed(&s));
+	if (WARN_ON_ONCE(seq_buf_putc(&s, '\0')))
+		s.buffer[PAGE_SIZE - 1] = '\0';
 
 	return s.buffer;
 }
@@ -1608,7 +1610,7 @@ void mem_cgroup_print_oom_context(struct
  */
 void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
 {
-	char *buf;
+	const char *buf;
 
 	pr_info("memory: usage %llukB, limit %llukB, failcnt %lu\n",
 		K((u64)page_counter_read(&memcg->memory)),
@@ -6373,7 +6375,7 @@ static int memory_events_local_show(stru
 static int memory_stat_show(struct seq_file *m, void *v)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
-	char *buf;
+	const char *buf;
 
 	buf = memory_stat_format(memcg);
 	if (!buf)
_

Patches currently in -mm which might be from songmuchun@bytedance.com are

kprobes-fix-kill-kprobe-which-has-been-marked-as-gone.patch
mm-memcontrol-add-the-missing-numa_stat-interface-for-cgroup-v2.patch
mm-memcontrol-fix-out-of-bounds-on-the-buf-returned-by-memory_stat_format.patch
mmhwpoison-refactor-soft_offline_huge_page-and-__soft_offline_page-fix-2.patch