Re: [syzbot] UBSAN: shift-out-of-bounds in profile_init

[Pavel Skripkin <paskripkin@gmail.com>]

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On Wed, 14 Jul 2021 05:47:21 -0700
syzbot <syzbot+e68c89a9510c159d9684@syzkaller.appspotmail.com> wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    3dbdb38e Merge branch 'for-5.14' of
> git://git.kernel.org/p.. git tree:       upstream
> console output:
> https://syzkaller.appspot.com/x/log.txt?x=11342328300000 kernel
> config:  https://syzkaller.appspot.com/x/.config?x=a1fcf15a09815757
> dashboard link:
> https://syzkaller.appspot.com/bug?extid=e68c89a9510c159d9684 syz
> repro:
> https://syzkaller.appspot.com/x/repro.syz?x=149a96d2300000 C
> reproducer:   https://syzkaller.appspot.com/x/repro.c?x=114e5bc4300000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the
> commit: Reported-by:
> syzbot+e68c89a9510c159d9684@syzkaller.appspotmail.com
> 

With clamp() call suggested by Tetsuo

#syz test
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master



With regards,
Pavel Skripkin

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From 6dadb86239173d28b1d36e974e000d39b088177e Mon Sep 17 00:00:00 2001
From: Pavel Skripkin <paskripkin@gmail.com>
Date: Fri, 16 Jul 2021 17:27:44 +0300
Subject: [PATCH] profiling: fix shift-out-of-bounds

/* ... */

Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---
 kernel/profile.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/profile.c b/kernel/profile.c
index c2ebddb5e974..c905931e3c3b 100644
--- a/kernel/profile.c
+++ b/kernel/profile.c
@@ -42,6 +42,7 @@ struct profile_hit {
 
 static atomic_t *prof_buffer;
 static unsigned long prof_len, prof_shift;
+#define MAX_PROF_SHIFT		(sizeof(prof_shift) * 8)
 
 int prof_on __read_mostly;
 EXPORT_SYMBOL_GPL(prof_on);
@@ -67,7 +68,7 @@ int profile_setup(char *str)
 		if (str[strlen(sleepstr)] == ',')
 			str += strlen(sleepstr) + 1;
 		if (get_option(&str, &par))
-			prof_shift = par;
+			prof_shift = clamp(par, 0, (int) MAX_PROF_SHIFT - 1);
 		pr_info("kernel sleep profiling enabled (shift: %ld)\n",
 			prof_shift);
 #else
@@ -78,7 +79,7 @@ int profile_setup(char *str)
 		if (str[strlen(schedstr)] == ',')
 			str += strlen(schedstr) + 1;
 		if (get_option(&str, &par))
-			prof_shift = par;
+			prof_shift = clamp(par, 0, (int) MAX_PROF_SHIFT - 1);
 		pr_info("kernel schedule profiling enabled (shift: %ld)\n",
 			prof_shift);
 	} else if (!strncmp(str, kvmstr, strlen(kvmstr))) {
@@ -86,11 +87,11 @@ int profile_setup(char *str)
 		if (str[strlen(kvmstr)] == ',')
 			str += strlen(kvmstr) + 1;
 		if (get_option(&str, &par))
-			prof_shift = par;
+			prof_shift = clamp(par, 0, (int) MAX_PROF_SHIFT - 1);
 		pr_info("kernel KVM profiling enabled (shift: %ld)\n",
 			prof_shift);
 	} else if (get_option(&str, &par)) {
-		prof_shift = par;
+		prof_shift = clamp(par, 0, (int) MAX_PROF_SHIFT - 1);
 		prof_on = CPU_PROFILING;
 		pr_info("kernel profiling enabled (shift: %ld)\n",
 			prof_shift);
-- 
2.32.0