+ acct-fix-potential-integer-overflow-in-encode_comp_t.patch added to mm-nonmm-unstable branch

+ acct-fix-potential-integer-overflow-in-encode_comp_t.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: acct: fix potential integer overflow in encode_comp_t()
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     acct-fix-potential-integer-overflow-in-encode_comp_t.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/acct-fix-potential-integer-overflow-in-encode_comp_t.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Zheng Yejian <zhengyejian1@huawei.com>
Subject: acct: fix potential integer overflow in encode_comp_t()
Date: Sat, 15 May 2021 22:06:31 +0800

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>
---

 kernel/acct.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/kernel/acct.c~acct-fix-potential-integer-overflow-in-encode_comp_t
+++ a/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.
 	 */
_

Patches currently in -mm which might be from zhengyejian1@huawei.com are

acct-fix-accuracy-loss-for-input-value-of-encode_comp_t.patch
acct-fix-potential-integer-overflow-in-encode_comp_t.patch