linux-kernel - Re: [syzbot] [input?] [usb?] UBSAN: shift-out-of-bounds in s32ton

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Message-ID: <6b1277a8-30a6-4d2b-9b25-93d105503ea3@kylinos.cn>
Date: Thu, 14 Nov 2024 10:19:51 +0800
From: Pei Xiao <xiaopei01@...inos.cn>
To: 67321ded.050a0220.a83d0.0016.GAE@...gle.com,
 syzbot+3fa2af55f15bd21cada9@...kaller.appspotmail.com,
 linux-kernel@...r.kernel.org
Subject: Re: [syzbot] [input?] [usb?] UBSAN: shift-out-of-bounds in s32ton

s32ton always be 0 when n>=32,add check n.

#syz test

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 81d6c734c8bc..ead1d338fa58 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -66,8 +66,11 @@ static s32 snto32(__u32 value, unsigned int n)

  static u32 s32ton(__s32 value, unsigned int n)
  {
-       s32 a = value >> (n - 1);
+       s32 a;

+       if (n >= 32)
+               return value;
+       a = value >> (n - 1);
         if (a && a != -1)
                 return value < 0 ? 1 << (n - 1) : (1 << (n - 1)) - 1;
         return value & ((1 << n) - 1);