[PATCH] bfs: Fix null pointer dereference in bfs_move_block

[Yuran Pereira]

Syzkaller reported a NULL pointer dereference in
bfs_move_block.

sb_getblk may return a NULL pointer, and if unchecked
this can lead to a NULL pointer dereference. This is
the case in bfs_move_block, where `new` is not checked
before being dereferenced in the memcpy call.

This patch adds a propper check to the return value of
sb_getblk, stored in `new` and ensures that any previously
allocated resource, is deallocated before returning with
an appropriate error code if the `new` pointer is NULL.

Closes: https://syzkaller.appspot.com/bug?extid=dc6ed11a88fb40d6e184
Signed-off-by: Yuran Pereira <yuran.pereira@xxxxxxxxxxx>
---
 fs/bfs/file.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/bfs/file.c b/fs/bfs/file.c
index adc2230079c6..8a97909b1484 100644
--- a/fs/bfs/file.c
+++ b/fs/bfs/file.c
@@ -38,7 +38,12 @@ static int bfs_move_block(unsigned long from, unsigned long to,
 	bh = sb_bread(sb, from);
 	if (!bh)
 		return -EIO;
+
 	new = sb_getblk(sb, to);
+	if (!new) {
+		bforget(bh);
+		return -ENOMEM;
+	}
 	memcpy(new->b_data, bh->b_data, bh->b_size);
 	mark_buffer_dirty(new);
 	bforget(bh);
-- 
2.25.1