linux-kernel - [PATCH 11/18] staging: gasket: always allow root open for write

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Date:   Fri, 13 Jul 2018 22:58:09 -0700
From:   Todd Poynor <toddpoynor@...il.com>
To:     Rob Springer <rspringer@...gle.com>,
        John Joseph <jnjoseph@...gle.com>,
        Ben Chan <benchan@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Zhongze Hu <frankhu@...omium.org>, Simon Que <sque@...omium.org>,
        Dmitry Torokhov <dtor@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        Todd Poynor <toddpoynor@...gle.com>
Subject: [PATCH 11/18] staging: gasket: always allow root open for write

From: Todd Poynor <toddpoynor@...gle.com>

Always allow root to open device for writing.

Drop special-casing of ioctl permissions for root vs. owner.

Reported-by: Dmitry Torokhov <dtor@...omium.org>
Signed-off-by: Zhongze Hu <frankhu@...omium.org>
Signed-off-by: Todd Poynor <toddpoynor@...gle.com>
---
 drivers/staging/gasket/apex_driver.c  |  9 +++------
 drivers/staging/gasket/gasket_core.c  |  8 +++++---
 drivers/staging/gasket/gasket_ioctl.c | 15 ++++++---------
 3 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/drivers/staging/gasket/apex_driver.c b/drivers/staging/gasket/apex_driver.c
index b1318482ba65..ffe11d8168ea 100644
--- a/drivers/staging/gasket/apex_driver.c
+++ b/drivers/staging/gasket/apex_driver.c
@@ -644,13 +644,10 @@ static bool is_gcb_in_reset(struct gasket_dev *gasket_dev)
 static uint apex_ioctl_check_permissions(struct file *filp, uint cmd)
 {
 	struct gasket_dev *gasket_dev = filp->private_data;
-	int root = capable(CAP_SYS_ADMIN);
-	int is_owner = gasket_dev->dev_info.ownership.is_owned &&
-		       current->tgid == gasket_dev->dev_info.ownership.owner;
+	fmode_t write;
 
-	if (root || is_owner)
-		return 1;
-	return 0;
+	write = filp->f_mode & FMODE_WRITE;
+	return write;
 }
 
 /*
diff --git a/drivers/staging/gasket/gasket_core.c b/drivers/staging/gasket/gasket_core.c
index 0c45c54254fb..5908964f0039 100644
--- a/drivers/staging/gasket/gasket_core.c
+++ b/drivers/staging/gasket/gasket_core.c
@@ -1101,6 +1101,7 @@ static int gasket_open(struct inode *inode, struct file *filp)
 	char task_name[TASK_COMM_LEN];
 	struct gasket_cdev_info *dev_info =
 	    container_of(inode->i_cdev, struct gasket_cdev_info, cdev);
+	int is_root = capable(CAP_SYS_ADMIN);
 
 	gasket_dev = dev_info->gasket_dev_ptr;
 	driver_desc = gasket_dev->internal_desc->driver_desc;
@@ -1114,7 +1115,7 @@ static int gasket_open(struct inode *inode, struct file *filp)
 		"Attempting to open with tgid %u (%s) (f_mode: 0%03o, "
 		"fmode_write: %d is_root: %u)",
 		current->tgid, task_name, filp->f_mode,
-		(filp->f_mode & FMODE_WRITE), capable(CAP_SYS_ADMIN));
+		(filp->f_mode & FMODE_WRITE), is_root);
 
 	/* Always allow non-writing accesses. */
 	if (!(filp->f_mode & FMODE_WRITE)) {
@@ -1128,8 +1129,9 @@ static int gasket_open(struct inode *inode, struct file *filp)
 		gasket_dev, "Current owner open count (owning tgid %u): %d.",
 		ownership->owner, ownership->write_open_count);
 
-	/* Opening a node owned by another TGID is an error (even root.) */
-	if (ownership->is_owned && ownership->owner != current->tgid) {
+	/* Opening a node owned by another TGID is an error (unless root) */
+	if (ownership->is_owned && ownership->owner != current->tgid &&
+	    !is_root) {
 		gasket_log_error(
 			gasket_dev,
 			"Process %u is opening a node held by %u.",
diff --git a/drivers/staging/gasket/gasket_ioctl.c b/drivers/staging/gasket/gasket_ioctl.c
index 4758083fb19b..23875fd465f6 100644
--- a/drivers/staging/gasket/gasket_ioctl.c
+++ b/drivers/staging/gasket/gasket_ioctl.c
@@ -180,7 +180,7 @@ long gasket_is_supported_ioctl(uint cmd)
  */
 static uint gasket_ioctl_check_permissions(struct file *filp, uint cmd)
 {
-	uint alive, root, device_owner;
+	uint alive;
 	fmode_t read, write;
 	struct gasket_dev *gasket_dev = (struct gasket_dev *)filp->private_data;
 
@@ -191,33 +191,30 @@ static uint gasket_ioctl_check_permissions(struct file *filp, uint cmd)
 			alive, gasket_dev->status);
 	}
 
-	root = capable(CAP_SYS_ADMIN);
 	read = filp->f_mode & FMODE_READ;
 	write = filp->f_mode & FMODE_WRITE;
-	device_owner = (gasket_dev->dev_info.ownership.is_owned &&
-			current->tgid == gasket_dev->dev_info.ownership.owner);
 
 	switch (cmd) {
 	case GASKET_IOCTL_RESET:
 	case GASKET_IOCTL_CLEAR_INTERRUPT_COUNTS:
-		return root || (write && device_owner);
+		return write;
 
 	case GASKET_IOCTL_PAGE_TABLE_SIZE:
 	case GASKET_IOCTL_SIMPLE_PAGE_TABLE_SIZE:
 	case GASKET_IOCTL_NUMBER_PAGE_TABLES:
-		return root || read;
+		return read;
 
 	case GASKET_IOCTL_PARTITION_PAGE_TABLE:
 	case GASKET_IOCTL_CONFIG_COHERENT_ALLOCATOR:
-		return alive && (root || (write && device_owner));
+		return alive && write;
 
 	case GASKET_IOCTL_MAP_BUFFER:
 	case GASKET_IOCTL_UNMAP_BUFFER:
-		return alive && (root || (write && device_owner));
+		return alive && write;
 
 	case GASKET_IOCTL_CLEAR_EVENTFD:
 	case GASKET_IOCTL_SET_EVENTFD:
-		return alive && (root || (write && device_owner));
+		return alive && write;
 	}
 
 	return 0; /* unknown permissions */
-- 
2.18.0.203.gfac676dfb9-goog