[PATCH] ntfs3: bound index head insertions by buffer capacity

[Yousef Alhouseen <alhouseenyousef@gmail.com>]

hdr_insert_head() shifts the existing index entries by ins_bytes without
checking that the resulting used size fits within hdr->total. A directory
index root larger than the newly allocated index buffer can therefore make
the memmove write beyond the buffer.

Reject insertions whose size would exceed the index header capacity and
make both split callers unwind the new node when that happens.

Fixes: 82cae269cfa9 ("fs/ntfs3: Add initialization of super block")
Reported-by: syzbot+45ef5a8d661162757547@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=45ef5a8d661162757547
Cc: stable@vger.kernel.org
Signed-off-by: Yousef Alhouseen <alhouseenyousef@gmail.com>
---
 fs/ntfs3/index.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/ntfs3/index.c b/fs/ntfs3/index.c
index 5344b29b0577..64e1be9b7aca 100644
--- a/fs/ntfs3/index.c
+++ b/fs/ntfs3/index.c
@@ -594,6 +594,8 @@ static const struct NTFS_DE *hdr_insert_head(struct INDEX_HDR *hdr,
 
 	if (!e)
 		return NULL;
+	if (size_add(used, ins_bytes) > le32_to_cpu(hdr->total))
+		return NULL;
 
 	/* Now we just make room for the inserted entries and jam it in. */
 	to_move = used - le32_to_cpu(hdr->de_off);
@@ -1743,7 +1745,10 @@ static int indx_insert_into_root(struct ntfs_index *indx, struct ntfs_inode *ni,
 	hdr_total = le32_to_cpu(hdr->total);
 
 	/* Copy root entries into new buffer. */
-	hdr_insert_head(hdr, re, to_move);
+	if (!hdr_insert_head(hdr, re, to_move)) {
+		err = -EINVAL;
+		goto out_put_n;
+	}
 
 	/* Update bitmap attribute. */
 	indx_mark_used(indx, ni, new_vbn >> indx->idx2vbn_bits);
@@ -1881,7 +1886,11 @@ indx_insert_into_buffer(struct ntfs_index *indx, struct ntfs_inode *ni,
 	/* Copy all the entries <= sp into the new buffer. */
 	de_t = hdr_first_de(hdr1);
 	to_copy = PtrOffset(de_t, sp);
-	hdr_insert_head(hdr2, de_t, to_copy);
+	if (!hdr_insert_head(hdr2, de_t, to_copy)) {
+		err = -EINVAL;
+		put_indx_node(n2);
+		goto out;
+	}
 
 	/* Remove all entries (sp including) from hdr1. */
 	used = used1 - to_copy - sp_size;
-- 
2.54.0