f2fs: fix compressed file start atomic write may cause data corruption

When compressed file has blocks, f2fs_ioc_start_atomic_write will succeed,
but compressed flag will be remained in inode. If write partial compreseed
cluster and commit atomic write will cause data corruption.

This is the reproduction process:
Step 1:
create a compressed file ,write 64K data , call fsync(), then the blocks
are write as compressed cluster.
Step2:
iotcl(F2FS_IOC_START_ATOMIC_WRITE)  --- this should be fail, but not.
write page 0 and page 3.
iotcl(F2FS_IOC_COMMIT_ATOMIC_WRITE)  -- page 0 and 3 write as normal file,
Step3:
drop cache.
read page 0-4   -- Since page 0 has a valid block address, read as
non-compressed cluster, page 1 and 2 will be filled with compressed data
or zero.

The root cause is, after commit 7eab7a6 ("f2fs: compress: remove
unneeded read when rewrite whole cluster"), in step 2, f2fs_write_begin()
only set target page dirty, and in f2fs_commit_inmem_pages(), we will write
partial raw pages into compressed cluster, result in corrupting compressed
cluster layout.

Fixes: 4c8ff70 ("f2fs: support data compression")
Fixes: 7eab7a6 ("f2fs: compress: remove unneeded read when rewrite whole cluster")
Reported-by: kernel test robot <[email protected]>
Reported-by: Dan Carpenter <[email protected]>
Signed-off-by: Fengnan Chang <[email protected]>
Reviewed-by: Chao Yu <[email protected]>
Signed-off-by: Jaegeuk Kim <[email protected]>

Author: Fengnan Chang

fs/f2fs/data.c

@@ -3363,7 +3363,7 @@ static int f2fs_write_begin(struct file *file, struct address_space *mapping,
 
 		*fsdata = NULL;
 
-		if (len == PAGE_SIZE)
+		if (len == PAGE_SIZE && !(f2fs_is_atomic_file(inode)))
 			goto repeat;
 
 		ret = f2fs_prepare_compress_overwrite(inode, pagep,

fs/f2fs/file.c

@@ -2009,7 +2009,10 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
 
 	inode_lock(inode);
 
-	f2fs_disable_compressed_file(inode);
+	if (!f2fs_disable_compressed_file(inode)) {
+		ret = -EINVAL;
+		goto out;
+	}
 
 	if (f2fs_is_atomic_file(inode)) {
 		if (is_inode_flag_set(inode, FI_ATOMIC_REVOKE_REQUEST))