[PATCH 5.18 746/879] ext4: avoid cycles in directory h-tree

Greg Kroah-Hartman
2022-06-08T00:33:47Z

From: Jan Kara <jack@suse.cz>

commit 3ba733f879c2a88910744647e41edeefbc0d92b2 upstream.

A maliciously corrupted filesystem can contain cycles in the h-tree
stored inside a directory. That can easily lead to the kernel corrupting
tree nodes that were already verified under its hands while doing a node
split and consequently accessing unallocated memory. Fix the problem by
verifying traversed block numbers are unique.

Cc: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220518093332.13986-2-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/ext4/namei.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)

--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -777,12 +777,14 @@ static struct dx_frame *
dx_probe(struct ext4_filename *fname, struct inode *dir,
struct dx_hash_info *hinfo, struct dx_frame *frame_in)
{
- unsigned count, indirect;
+ unsigned count, indirect, level, i;
struct dx_entry *at, *entries, *p, *q, *m;
struct dx_root *root;
struct dx_frame *frame = frame_in;
struct dx_frame *ret_err = ERR_PTR(ERR_BAD_DX_DIR);
u32 hash;
+ ext4_lblk_t block;
+ ext4_lblk_t blocks[EXT4_HTREE_LEVEL];

memset(frame_in, 0, EXT4_HTREE_LEVEL * sizeof(frame_in[0]));
frame->bh = ext4_read_dirblock(dir, 0, INDEX);
@@ -854,6 +856,8 @@ dx_probe(struct ext4_filename *fname, st
}

dxtrace(printk("Look up %x", hash));
+ level = 0;
+ blocks[0] = 0;
while (1) {
count = dx_get_count(entries);
if (!count || count > dx_get_limit(entries)) {
@@ -882,15 +886,27 @@ dx_probe(struct ext4_filename *fname, st
dx_get_block(at)));
frame->entries = entries;
frame->at = at;
- if (!indirect--)
+
+ block = dx_get_block(at);
+ for (i = 0; i <= level; i++) {
+ if (blocks[i] == block) {
+ ext4_warning_inode(dir,
+ "dx entry: tree cycle block %u points back to block %u",
+ blocks[level], block);
+ goto fail;
+ }
+ }
+ if (++level > indirect)
return frame;
+ blocks[level] = block;
frame++;
- frame->bh = ext4_read_dirblock(dir, dx_get_block(at), INDEX);
+ frame->bh = ext4_read_dirblock(dir, block, INDEX);
if (IS_ERR(frame->bh)) {
ret_err = (struct dx_frame *) frame->bh;
frame->bh = NULL;
goto fail;
}
+
entries = ((struct dx_node *) frame->bh->b_data)->entries;

if (dx_get_limit(entries) != dx_node_limit(dir)) {