[PATCH AUTOSEL 4.14 7/8] acct: fix potential integer overflow in encode_comp_t()

[Sasha Levin]

From: Zheng Yejian <zhengyejian1@xxxxxxxxxx>

[ Upstream commit c5f31c655bcc01b6da53b836ac951c1556245305 ]

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@xxxxxxxxxx
Signed-off-by: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
Cc: Hanjun Guo <guohanjun@xxxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Zhang Jinhao <zhangjinhao2@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/acct.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/acct.c b/kernel/acct.c
index 354578d253d5..bec90c267ac6 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -331,6 +331,8 @@ static comp_t encode_comp_t(unsigned long value)
 		exp++;
 	}
 
+	if (exp > (((comp_t) ~0U) >> MANTSIZE))
+		return (comp_t) ~0U;
 	/*
 	 * Clean it up and polish it off.
 	 */
-- 
2.35.1