[PATCH] btrfs: Fix possible NULL pointer dereference in btrfs selftest

[Qu Wenruo <wqu@suse.com>]

When CONFIG_BTRFS_FS_RUN_SANITY_TESTS is enabled, btrfs will run
selftest at module load time.

During selftest, we allocate extent buffer using
alloc_test_extent_buffer(), instead of alloc_test_extent_buffer().

The problem is, unlike alloc_extent_buffer(),
alloc_test_extent_buffer() can return NULL pointer instead of error
pointer, and callers all expect error pointer other than NULL pointer.

So this could lead to NULL pointer dereference during selftest.

Fix it by returning error pointer in alloc_test_extent_buffer().

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent_io.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 52abe4082680..a7db78f49fdb 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4862,12 +4862,14 @@ struct extent_buffer *alloc_test_extent_buffer(struct btrfs_fs_info *fs_info,
 		return eb;
 	eb = alloc_dummy_extent_buffer(fs_info, start);
 	if (!eb)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 	eb->fs_info = fs_info;
 again:
 	ret = radix_tree_preload(GFP_NOFS);
-	if (ret)
-		goto free_eb;
+	if (ret) {
+		btrfs_release_extent_buffer(eb);
+		return ERR_PTR(ret);
+	}
 	spin_lock(&fs_info->buffer_lock);
 	ret = radix_tree_insert(&fs_info->buffer_radix,
 				start >> PAGE_SHIFT, eb);
@@ -4875,18 +4877,16 @@ struct extent_buffer *alloc_test_extent_buffer(struct btrfs_fs_info *fs_info,
 	radix_tree_preload_end();
 	if (ret == -EEXIST) {
 		exists = find_extent_buffer(fs_info, start);
-		if (exists)
-			goto free_eb;
-		else
-			goto again;
+		if (exists) {
+			btrfs_release_extent_buffer(eb);
+			return exists;
+		}
+		goto again;
 	}
 	check_buffer_tree_ref(eb);
 	set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);
 
 	return eb;
-free_eb:
-	btrfs_release_extent_buffer(eb);
-	return exists;
 }
 #endif
 
-- 
2.20.1