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Subject[PATCH] mm: memcontrol: Fix out-of-bounds on the buf returned by memory_stat_format
Date
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.

Fixes: c8713d0b2312 ("mm: memcontrol: dump memory.stat during cgroup OOM")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
mm/memcontrol.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f2ef9a770eeb..20c8a1080074 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1492,12 +1492,13 @@ static bool mem_cgroup_wait_acct_move(struct mem_cgroup *memcg)
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;

@@ -1606,7 +1607,8 @@ static char *memory_stat_format(struct mem_cgroup *memcg)
#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;
}
@@ -1644,7 +1646,7 @@ void mem_cgroup_print_oom_context(struct mem_cgroup *memcg, struct task_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)),
@@ -6415,7 +6417,7 @@ static int memory_events_local_show(struct seq_file *m, void *v)
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)
--
2.20.1
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