acct: fix potential integer overflow in encode_comp_t()

The integer overflow is descripted with following codes:
  > 317 static comp_t encode_comp_t(u64 value)
  > 318 {
  > 319         int exp, rnd;
    ......
  > 341         exp <<= MANTSIZE;
  > 342         exp += value;
  > 343         return exp;
  > 344 }

Currently comp_t is defined as type of '__u16', but the variable 'exp' is
type of 'int', so overflow would happen when variable 'exp' in line 343 is
greater than 65535.

Link: https://lkml.kernel.org/r/20210515140631.369106-3-zhengyejian1@huawei.com
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Cc: Hanjun Guo <guohanjun@huawei.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zhang Jinhao <zhangjinhao2@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/acct.c b/kernel/acct.c
index 31b09cf..010667c 100644 (file)
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -350,6 +350,8 @@ static comp_t encode_comp_t(u64 value)
                exp++;
        }
 
+       if (exp > (((comp_t) ~0U) >> MANTSIZE))
+               return (comp_t) ~0U;
        /*
         * Clean it up and polish it off.
         */