[PATCH] sched/core: check format and overflows in cgroup2 cpu.max

[Konstantin Khlebnikov]

Cgroup2 interface for cpu bandwidth limit has some flaws:

- on stack buffer overflow
- no checks for valid format or trailing garbage
- no checks for integer overflows

This patch fixes all these flaws.

Fixes: 0d5936344f30 ("sched: Implement interface for cgroup unified hierarchy")
Signed-off-by: Konstantin Khlebnikov <khlebni...@yandex-team.ru>
---
 kernel/sched/core.c |   29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5f46aa335b28..123b1910bc2e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6947,19 +6947,34 @@ static int __maybe_unused cpu_period_quota_parse(char 
*buf,
                                                 u64 *periodp, u64 *quotap)
 {
        char tok[21];   /* U64_MAX */
+       int ret, len;
 
-       if (!sscanf(buf, "%s %llu", tok, periodp))
+       if (sscanf(buf, "%20s %n", tok, &len) != 1)
                return -EINVAL;
 
-       *periodp *= NSEC_PER_USEC;
-
-       if (sscanf(tok, "%llu", quotap))
-               *quotap *= NSEC_PER_USEC;
-       else if (!strcmp(tok, "max"))
+       ret = kstrtou64(tok, 10, quotap);
+       if (ret) {
+               if (strcmp(tok, "max"))
+                       return ret;
                *quotap = RUNTIME_INF;
-       else
+       } else if (*quotap <= U64_MAX / NSEC_PER_USEC) {
+               *quotap *= NSEC_PER_USEC;
+       } else
                return -EINVAL;
 
+       buf += len;
+       if (*buf) {
+               if (sscanf(buf, "%20s %n", tok, &len) != 1 || buf[len])
+                       return -EINVAL;
+               ret = kstrtou64(tok, 10, periodp);
+               if (ret)
+                       return ret;
+               if (*periodp > U64_MAX / NSEC_PER_USEC)
+                       return -EINVAL;
+       }
+
+       *periodp *= NSEC_PER_USEC;
+
        return 0;
 }