commit db0248427f18fda6531ebe63273094069bf29e83
author Jaegeuk Kim <jaegeuk@google.com> Thu Jul 06 19:12:22 2017 -0700
committer Daniel Rosenberg <drosen@google.com> Tue Aug 08 16:39:31 2017 -0700
tree 44c658bc6854d087ad5ceb311e993a8ff6fe045b
parent ce863f8af4595620791f79fedcdf525aa8faa677

ANDROID: sdcardfs: override credential for ioctl to lower fs

Otherwise, lower_fs->ioctl() fails due to inode_owner_or_capable().

Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
Bug: 63260873
Change-Id: I623a6c7c5f8a3cbd7ec73ef89e18ddb093c43805

fs/sdcardfs/file.c

diff --git a/fs/sdcardfs/file.c b/fs/sdcardfs/file.c
index 6076c34..5ac0b0b 100644
--- a/fs/sdcardfs/file.c
+++ b/fs/sdcardfs/file.c
@@ -104,12 +104,19 @@
 {
 	long err = -ENOTTY;
 	struct file *lower_file;
+	const struct cred *saved_cred = NULL;
+	struct dentry *dentry = file->f_path.dentry;
+	struct sdcardfs_sb_info *sbi = SDCARDFS_SB(dentry->d_sb);
 
 	lower_file = sdcardfs_lower_file(file);
 
 	/* XXX: use vfs_ioctl if/when VFS exports it */
 	if (!lower_file || !lower_file->f_op)
 		goto out;
+
+	/* save current_cred and override it */
+	OVERRIDE_CRED(sbi, saved_cred, SDCARDFS_I(file_inode(file)));
+
 	if (lower_file->f_op->unlocked_ioctl)
 		err = lower_file->f_op->unlocked_ioctl(lower_file, cmd, arg);
 
@@ -117,6 +124,7 @@
 	if (!err)
 		sdcardfs_copy_and_fix_attrs(file_inode(file),
 				      file_inode(lower_file));
+	REVERT_CRED(saved_cred);
 out:
 	return err;
 }
@@ -127,15 +135,23 @@
 {
 	long err = -ENOTTY;
 	struct file *lower_file;
+	const struct cred *saved_cred = NULL;
+	struct dentry *dentry = file->f_path.dentry;
+	struct sdcardfs_sb_info *sbi = SDCARDFS_SB(dentry->d_sb);
 
 	lower_file = sdcardfs_lower_file(file);
 
 	/* XXX: use vfs_ioctl if/when VFS exports it */
 	if (!lower_file || !lower_file->f_op)
 		goto out;
+
+	/* save current_cred and override it */
+	OVERRIDE_CRED(sbi, saved_cred, SDCARDFS_I(file_inode(file)));
+
 	if (lower_file->f_op->compat_ioctl)
 		err = lower_file->f_op->compat_ioctl(lower_file, cmd, arg);
 
+	REVERT_CRED(saved_cred);
 out:
 	return err;
 }