linux-kernel - [PATCH] profiling: fix shift-out-of-bounds in profile

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Date:   Fri, 16 Jul 2021 22:04:09 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     penguin-kernel@...ove.SAKURA.ne.jp, rostedt@...dmis.org,
        tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org,
        Pavel Skripkin <paskripkin@...il.com>,
        syzbot+e68c89a9510c159d9684@...kaller.appspotmail.com,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Subject: [PATCH] profiling: fix shift-out-of-bounds in profile_setup

Syzbot reported shift-out-of-bounds bug in profile_init().
The problem was in incorrect prof_shift. Since prof_shift value comes from
userspace we need to check this value to avoid too big shift.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-and-tested-by: syzbot+e68c89a9510c159d9684@...kaller.appspotmail.com
Suggested-by: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Signed-off-by: Pavel Skripkin <paskripkin@...il.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