linux-kernel - [PATCH] binder: remove unneeded size check code

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Date:   Tue, 15 Nov 2022 20:03:51 +0800
From:   "Jiazi.Li" <jqqlijiazi@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>, arve@...roid.com,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <brauner@...nel.org>,
        Carlos Llamas <cmllamas@...gle.com>
Cc:     "Jiazi.Li" <jiazi.li@...nssion.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] binder: remove unneeded size check code

In binder_ioctl function, the legitimacy check of cmd size has been
done in switch-case code:
switch (cmd) {
	case BINDER_WRITE_READ;//BINDER_WRITE_READ contains size info

So unneeded do size check in binder_ioctl and binder_ioctl_write_read
again.

In the following version of Google GKI:

Linux version 5.10.110-android12-9-00011-g2c814f559132-ab8969555

It seems that the compiler has made optimization and has not passed
cmd parameters to binder_ioctl_write_read:
<binder_ioctl+628>:  mov     w8, #0x6201                     // #25089
<binder_ioctl+632>:  movk    w8, #0xc030, lsl #16
<binder_ioctl+636>:  cmp     w20, w8
<binder_ioctl+640>:  b.ne    0xffffffda8aa97880 <binder_ioctl+3168>
<binder_ioctl+644>:  mov     x0, x23 //filp
<binder_ioctl+648>:  mov     x1, x27 //arg
<binder_ioctl+652>:  mov     x2, x22 //thread
<binder_ioctl+656>:  bl      0xffffffda8aa9e6e4 <binder_ioctl_write_read>
<binder_ioctl+660>:  mov     w26, w0

Signed-off-by: Jiazi.Li <jiazi.li@...nssion.com>
---
 drivers/android/binder.c | 15 ++-------------
 1 file changed, 2 insertions(+), 13 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 880224ec6abb..48e5a3531282 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -5006,20 +5006,14 @@ static __poll_t binder_poll(struct file *filp,
 	return 0;
 }
 
-static int binder_ioctl_write_read(struct file *filp,
-				unsigned int cmd, unsigned long arg,
+static int binder_ioctl_write_read(struct file *filp, unsigned long arg,
 				struct binder_thread *thread)
 {
 	int ret = 0;
 	struct binder_proc *proc = filp->private_data;
-	unsigned int size = _IOC_SIZE(cmd);
 	void __user *ubuf = (void __user *)arg;
 	struct binder_write_read bwr;
 
-	if (size != sizeof(struct binder_write_read)) {
-		ret = -EINVAL;
-		goto out;
-	}
 	if (copy_from_user(&bwr, ubuf, sizeof(bwr))) {
 		ret = -EFAULT;
 		goto out;
@@ -5296,7 +5290,6 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	int ret;
 	struct binder_proc *proc = filp->private_data;
 	struct binder_thread *thread;
-	unsigned int size = _IOC_SIZE(cmd);
 	void __user *ubuf = (void __user *)arg;
 
 	/*pr_info("binder_ioctl: %d:%d %x %lx\n",
@@ -5318,7 +5311,7 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 
 	switch (cmd) {
 	case BINDER_WRITE_READ:
-		ret = binder_ioctl_write_read(filp, cmd, arg, thread);
+		ret = binder_ioctl_write_read(filp, arg, thread);
 		if (ret)
 			goto err;
 		break;
@@ -5361,10 +5354,6 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	case BINDER_VERSION: {
 		struct binder_version __user *ver = ubuf;
 
-		if (size != sizeof(struct binder_version)) {
-			ret = -EINVAL;
-			goto err;
-		}
 		if (put_user(BINDER_CURRENT_PROTOCOL_VERSION,
 			     &ver->protocol_version)) {
 			ret = -EINVAL;
-- 
2.17.1