[PATCH 2/2] acct: Fix potential integer overflow in encode_comp_t()

[Zheng Yejian]

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.

Signed-off-by: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
---
 kernel/acct.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/acct.c b/kernel/acct.c
index 9e143ed5b5d0..4182b92cf3df 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -331,6 +331,8 @@ 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.
 	 */
-- 
2.17.1