2022-04-29 01:14:37

by Jan Kara

[permalink] [raw]
Subject: [PATCH 2/2] ext4: Avoid cycles in directory h-tree

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: [email protected]
Signed-off-by: Jan Kara <[email protected]>
---
fs/ext4/namei.c | 24 ++++++++++++++++++++----
1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index ca6ee9940599..06441ad6104d 100644
--- 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, struct inode *dir,
}

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, struct inode *dir,
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;
+ }
+ }
+ blocks[++level] = block;
+ if (level > indirect)
return frame;
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)) {
@@ -1278,7 +1294,7 @@ static int dx_make_map(struct inode *dir, struct buffer_head *bh,
count++;
cond_resched();
}
- de = ext4_next_entry(de, blocksize);
+ de = ext4_next_entry(de, dir->i_sb->s_blocksize);
}
return count;
}
--
2.34.1