linux-kernel - Re: [syzbot] [ext4?] KASAN: use-after-free Write in ext4_insert

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Message-ID: <tencent_982EDE6ECA0C9127E346D612C6866189AC06@qq.com>
Date: Sun, 27 Oct 2024 18:26:54 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+0c99c3f90699936c1e77@...kaller.appspotmail.com
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [ext4?] KASAN: use-after-free Write in ext4_insert_dentry

check next directory entry space if it is too smaller than file name exit dentry insert and return -EINVAL 

#syz test

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 44b0d418143c..dbd062f80c22 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2834,7 +2834,7 @@ extern int ext4_find_dest_de(struct inode *dir, struct inode *inode,
 			     void *buf, int buf_size,
 			     struct ext4_filename *fname,
 			     struct ext4_dir_entry_2 **dest_de);
-void ext4_insert_dentry(struct inode *dir, struct inode *inode,
+int ext4_insert_dentry(struct inode *dir, struct inode *inode,
 			struct ext4_dir_entry_2 *de,
 			int buf_size,
 			struct ext4_filename *fname);
diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index 3536ca7e4fcc..e318b13459d1 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -1022,7 +1022,9 @@ static int ext4_add_dirent_to_inline(handle_t *handle,
 					    EXT4_JTR_NONE);
 	if (err)
 		return err;
-	ext4_insert_dentry(dir, inode, de, inline_size, fname);
+	err = ext4_insert_dentry(dir, inode, de, inline_size, fname);
+	if (err)
+		return err;
 
 	ext4_show_inline_dir(dir, iloc->bh, inline_start, inline_size);
 
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 790db7eac6c2..4ce1b207a4c0 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -2084,24 +2084,38 @@ int ext4_find_dest_de(struct inode *dir, struct inode *inode,
 	return 0;
 }
 
-void ext4_insert_dentry(struct inode *dir,
+int ext4_check_next_dentry(struct inode *dir,
 			struct inode *inode,
 			struct ext4_dir_entry_2 *de,
 			int buf_size,
 			struct ext4_filename *fname)
 {
-
 	int nlen, rlen;
 
 	nlen = ext4_dir_rec_len(de->name_len, dir);
 	rlen = ext4_rec_len_from_disk(de->rec_len, buf_size);
 	if (de->inode) {
-		struct ext4_dir_entry_2 *de1 =
+		struct ext4_dir_entry_2 *nde =
 			(struct ext4_dir_entry_2 *)((char *)de + nlen);
-		de1->rec_len = ext4_rec_len_to_disk(rlen - nlen, buf_size);
+		nde->rec_len = ext4_rec_len_to_disk(rlen - nlen, buf_size);
 		de->rec_len = ext4_rec_len_to_disk(nlen, buf_size);
-		de = de1;
+		de = nde;
+		rlen = ext4_rec_len_from_disk(de->rec_len, buf_size);
+		return fname_len(fname) > rlen - EXT4_BASE_DIR_LEN;
 	}
+
+	return 0;
+}
+
+int ext4_insert_dentry(struct inode *dir,
+			struct inode *inode,
+			struct ext4_dir_entry_2 *de,
+			int buf_size,
+			struct ext4_filename *fname)
+{
+	if (ext4_check_next_dentry(dir, inode, de, buf_size, fname))
+		return -EINVAL;
+
 	de->file_type = EXT4_FT_UNKNOWN;
 	de->inode = cpu_to_le32(inode->i_ino);
 	ext4_set_de_type(inode->i_sb, de, inode->i_mode);
@@ -2114,6 +2128,8 @@ void ext4_insert_dentry(struct inode *dir,
 		EXT4_DIRENT_HASHES(de)->minor_hash =
 						cpu_to_le32(hinfo->minor_hash);
 	}
+
+	return 0;
 }
 
 /*
@@ -2151,7 +2167,11 @@ static int add_dirent_to_buf(handle_t *handle, struct ext4_filename *fname,
 	}
 
 	/* By now the buffer is marked for journaling */
-	ext4_insert_dentry(dir, inode, de, blocksize, fname);
+	err = ext4_insert_dentry(dir, inode, de, blocksize, fname);
+	if (err) {
+		ext4_std_error(dir->i_sb, err);
+		return err;
+	}
 
 	/*
 	 * XXX shouldn't update any times until successful