linux-kernel - Re: [syzbot] [hardening?] [mm?] BUG: bad usercopy in fpa

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Message-ID: <1fec6a8b-7083-4b08-858a-0793f996ed52@I-love.SAKURA.ne.jp>
Date: Tue, 5 Mar 2024 19:17:35 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: syzbot <syzbot+cb76c2983557a07cdb14@...kaller.appspotmail.com>,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [hardening?] [mm?] BUG: bad usercopy in fpa_set

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

diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index c421a899fc84..29b28961637c 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -573,8 +573,10 @@ static int fpa_get(struct task_struct *target,
 		   const struct user_regset *regset,
 		   struct membuf to)
 {
-	return membuf_write(&to, &task_thread_info(target)->fpstate,
-				 sizeof(struct user_fp));
+	struct thread_info *thread = task_thread_info(target);
+
+	return membuf_write(&to, &thread->fpstate,
+				 sizeof(thread->fpstate));
 }
 
 static int fpa_set(struct task_struct *target,
@@ -586,7 +588,7 @@ static int fpa_set(struct task_struct *target,
 
 	return user_regset_copyin(&pos, &count, &kbuf, &ubuf,
 		&thread->fpstate,
-		0, sizeof(struct user_fp));
+		0, sizeof(thread->fpstate));
 }
 
 #ifdef CONFIG_VFP