linux-kernel - Re: [syzbot] UBSAN: shift-out-of-bounds in profile

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Date:   Fri, 16 Jul 2021 15:24:40 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     syzbot <syzbot+e68c89a9510c159d9684@...kaller.appspotmail.com>
Cc:     linux-kernel@...r.kernel.org, penguin-kernel@...ove.SAKURA.ne.jp,
        rostedt@...dmis.org, syzkaller-bugs@...glegroups.com,
        tglx@...utronix.de
Subject: Re: [syzbot] UBSAN: shift-out-of-bounds in profile_init

On Wed, 14 Jul 2021 05:47:21 -0700
syzbot <syzbot+e68c89a9510c159d9684@...kaller.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@...kaller.appspotmail.com
> 
> kernel profiling enabled (shift: 1000000)
> ================================================================================
> UBSAN: shift-out-of-bounds in kernel/profile.c:110:31
> shift exponent 1000000 is too large for 64-bit type 'long int'
> CPU: 0 PID: 8453 Comm: syz-executor969 Tainted: G        W
> 5.13.0-syzkaller #0 Hardware name: Google Google Compute
> Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:96
>  ubsan_epilogue+0xb/0x5a lib/ubsan.c:148
>  __ubsan_handle_shift_out_of_bounds.cold+0xb1/0x181 lib/ubsan.c:327
>  profile_init+0xfc/0x110 kernel/profile.c:110
>  profiling_store+0x5e/0xd0 kernel/ksysfs.c:80
>  kobj_attr_store+0x50/0x80 lib/kobject.c:856
>  sysfs_kf_write+0x110/0x160 fs/sysfs/file.c:139


I believe, something like this should fix it:


diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
index 35859da8bd4f..ca075d9f671a 100644
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -76,7 +76,9 @@ static ssize_t profiling_store(struct kobject *kobj,
 	 * has a ton of callers and is not const.  It is
 	 * easiest to cast it away here.
 	 */
-	profile_setup((char *)buf);
+	ret = profile_setup((char *)buf);
+	if (!ret)
+		return -EINVAL;
 	ret = profile_init();
 	if (ret)
 		return ret;
diff --git a/kernel/profile.c b/kernel/profile.c
index c2ebddb5e974..5c61677030f4 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);
@@ -66,8 +67,11 @@ int profile_setup(char *str)
 		prof_on = SLEEP_PROFILING;
 		if (str[strlen(sleepstr)] == ',')
 			str += strlen(sleepstr) + 1;
-		if (get_option(&str, &par))
+		if (get_option(&str, &par)) {
+			if (par >= MAX_PROF_SHIFT)
+				return 0;
 			prof_shift = par;
+		}
 		pr_info("kernel sleep profiling enabled (shift: %ld)\n",
 			prof_shift);
 #else
@@ -77,19 +81,27 @@ int profile_setup(char *str)
 		prof_on = SCHED_PROFILING;
 		if (str[strlen(schedstr)] == ',')
 			str += strlen(schedstr) + 1;
-		if (get_option(&str, &par))
+		if (get_option(&str, &par)) {
+			if (par >= MAX_PROF_SHIFT)
+				return 0;
 			prof_shift = par;
+		}
 		pr_info("kernel schedule profiling enabled (shift: %ld)\n",
 			prof_shift);
 	} else if (!strncmp(str, kvmstr, strlen(kvmstr))) {
 		prof_on = KVM_PROFILING;
 		if (str[strlen(kvmstr)] == ',')
 			str += strlen(kvmstr) + 1;
-		if (get_option(&str, &par))
+		if (get_option(&str, &par)) {
+			if (par >= MAX_PROF_SHIFT)
+				return 0;
 			prof_shift = par;
+		}
 		pr_info("kernel KVM profiling enabled (shift: %ld)\n",
 			prof_shift);
 	} else if (get_option(&str, &par)) {
+		if (par >= MAX_PROF_SHIFT)
+			return 0;
 		prof_shift = par;
 		prof_on = CPU_PROFILING;
 		pr_info("kernel profiling enabled (shift: %ld)\n",

 

But this function can be called not only from sysfs and I can't
understand will my patch break something or not. And, I think, error
message is needed somewhere here to inform callers about wrong shift
value.


Thoughts?


-- 
With regards,
Pavel Skripkin