Re: [syzbot] [hardening?] [mm?] BUG: bad usercopy in fpa_set

[Tetsuo Handa]

#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..b47e56a87dfa 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
@@ -690,7 +692,7 @@ static const struct user_regset arm_regsets[] = {
 		 * of sizes, so pretend that the registers are word-sized:
 		 */
 		.core_note_type = NT_PRFPREG,
-		.n = sizeof(struct user_fp) / sizeof(u32),
+		.n = sizeof(union fp_state) / sizeof(u32),
 		.size = sizeof(u32),
 		.align = sizeof(u32),
 		.regset_get = fpa_get,