block: check bdev_read_only() from blkdev_get()

bdev read-only status can be queried using bdev_read_only() and may
change while the device is being opened.  Enforce it by checking it
from blkdev_get() after open succeeds.

This makes bdev_read_only() check in open_bdev_exclusive() and
fsg_lun_open() unnecessary.  Drop them.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: linux-usb@vger.kernel.org

2 files changed, 8 insertions, 10 deletions

diff --git a/drivers/usb/gadget/storage_common.c b/drivers/usb/gadget/storage_common.c
index 3b513bafaf2a..b015561fd602 100644
--- a/drivers/usb/gadget/storage_common.c
+++ b/drivers/usb/gadget/storage_common.c
@@ -543,7 +543,7 @@ static int fsg_lun_open(struct fsg_lun *curlun, const char *filename)
         ro = curlun->initially_ro;
         if (!ro) {
                 filp = filp_open(filename, O_RDWR | O_LARGEFILE, 0);
-                if (-EROFS == PTR_ERR(filp))
+                if (PTR_ERR(filp) == -EROFS || PTR_ERR(filp) == -EACCES)
                         ro = 1;
         }
         if (ro)
@@ -558,10 +558,7 @@ static int fsg_lun_open(struct fsg_lun *curlun, const char *filename)
 
         if (filp->f_path.dentry)
                 inode = filp->f_path.dentry->d_inode;
-        if (inode && S_ISBLK(inode->i_mode)) {
-                if (bdev_read_only(inode->i_bdev))
-                        ro = 1;
-        } else if (!inode || !S_ISREG(inode->i_mode)) {
+        if (!inode || (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode))) {
                 LINFO(curlun, "invalid file type: %s\n", filename);
                 goto out;
         }
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 269bfbbd10fc..606a5259f87f 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1149,6 +1149,12 @@ int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
 
         res = __blkdev_get(bdev, mode, 0);
 
+        /* __blkdev_get() may alter read only status, check it afterwards */
+        if (!res && (mode & FMODE_WRITE) && bdev_read_only(bdev)) {
+                __blkdev_put(bdev, mode, 0);
+                res = -EACCES;
+        }
+
         if (whole) {
                 /* finish claiming */
                 spin_lock(&bdev_lock);
@@ -1453,11 +1459,6 @@ struct block_device *open_bdev_exclusive(const char *path, fmode_t mode, void *h
         if (error)
                 return ERR_PTR(error);
 
-        if ((mode & FMODE_WRITE) && bdev_read_only(bdev)) {
-                blkdev_put(bdev, mode);
-                return ERR_PTR(-EACCES);
-        }
-
         return bdev;
 }