f2fs: fix to avoid mmap vs set_compress_option case

Compression option in inode should not be changed after they have
been used, however, it may happen in below race case:

Thread A				Thread B
- f2fs_ioc_set_compress_option
 - check f2fs_is_mmap_file()
 - check get_dirty_pages()
 - check F2FS_HAS_BLOCKS()
					- f2fs_file_mmap
					 - set_inode_flag(FI_MMAP_FILE)
					- fault
					 - do_page_mkwrite
					  - f2fs_vm_page_mkwrite
					  - f2fs_get_block_locked
					 - fault_dirty_shared_page
					  - set_page_dirty
 - update i_compress_algorithm
 - update i_log_cluster_size
 - update i_cluster_size

Avoid such race condition by covering f2fs_file_mmap() w/ i_sem lock,
meanwhile add mmap file check condition in f2fs_may_compress() as well.

Fixes: e1e8debec656 ("f2fs: add F2FS_IOC_SET_COMPRESS_OPTION ioctl")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 18 insertions, 5 deletions

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 093039dee992..d9073afe021f 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -526,7 +526,11 @@ static int f2fs_file_mmap(struct file *file, struct vm_area_struct *vma)
 
 	file_accessed(file);
 	vma->vm_ops = &f2fs_file_vm_ops;
+
+	f2fs_down_read(&F2FS_I(inode)->i_sem);
 	set_inode_flag(inode, FI_MMAP_FILE);
+	f2fs_up_read(&F2FS_I(inode)->i_sem);
+
 	return 0;
 }
 
@@ -1919,12 +1923,19 @@ static int f2fs_setflags_common(struct inode *inode, u32 iflags, u32 mask)
 			int err = f2fs_convert_inline_inode(inode);
 			if (err)
 				return err;
-			if (!f2fs_may_compress(inode))
-				return -EINVAL;
-			if (S_ISREG(inode->i_mode) && F2FS_HAS_BLOCKS(inode))
+
+			f2fs_down_write(&F2FS_I(inode)->i_sem);
+			if (!f2fs_may_compress(inode) ||
+					(S_ISREG(inode->i_mode) &&
+					F2FS_HAS_BLOCKS(inode))) {
+				f2fs_up_write(&F2FS_I(inode)->i_sem);
 				return -EINVAL;
-			if (set_compress_context(inode))
-				return -EOPNOTSUPP;
+			}
+			err = set_compress_context(inode);
+			f2fs_up_write(&F2FS_I(inode)->i_sem);
+
+			if (err)
+				return err;
 		}
 	}
 
@@ -3976,6 +3987,7 @@ static int f2fs_ioc_set_compress_option(struct file *filp, unsigned long arg)
 	file_start_write(filp);
 	inode_lock(inode);
 
+	f2fs_down_write(&F2FS_I(inode)->i_sem);
 	if (f2fs_is_mmap_file(inode) || get_dirty_pages(inode)) {
 		ret = -EBUSY;
 		goto out;
@@ -3995,6 +4007,7 @@ static int f2fs_ioc_set_compress_option(struct file *filp, unsigned long arg)
 		f2fs_warn(sbi, "compression algorithm is successfully set, "
 			"but current kernel doesn't support this algorithm.");
 out:
+	f2fs_up_write(&F2FS_I(inode)->i_sem);
 	inode_unlock(inode);
 	file_end_write(filp);