Re: [syzbot] [lsm?] KASAN: slab-use-after-free Read in security_inode_follow_link

[Hillf Danton <hdanton@sina.com>]

> Date: Fri, 29 May 2026 13:01:28 -0700	[thread overview]
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    eb3f4b7426cf Merge tag 'nfsd-7.1-2' of git://git.kernel.or..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17dae52e580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=8118209836970b54
> dashboard link: https://syzkaller.appspot.com/bug?extid=0962e3a1af6d5e26a52c
> compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14427ed2580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=109e452e580000

#syz test

--- x/fs/namei.c
+++ y/fs/namei.c
@@ -5529,11 +5529,12 @@ int filename_unlinkat(int dfd, struct fi
 	struct dentry *dentry;
 	struct path path;
 	struct qstr last;
-	int type;
+	int type, loop;
 	struct inode *inode;
 	struct delegated_inode delegated_inode = { };
 	unsigned int lookup_flags = 0;
 retry:
+	loop = 0;
 	error = filename_parentat(dfd, name, lookup_flags, &path, &last, &type);
 	if (error)
 		return error;
@@ -5545,7 +5546,6 @@ retry:
 	error = mnt_want_write(path.mnt);
 	if (error)
 		goto exit_path_put;
-retry_deleg:
 	dentry = start_dirop(path.dentry, &last, lookup_flags);
 	error = PTR_ERR(dentry);
 	if (IS_ERR(dentry))
@@ -5561,7 +5561,6 @@ retry_deleg:
 		goto exit_drop_write;
 	}
 	inode = dentry->d_inode;
-	ihold(inode);
 	error = security_path_unlink(&path, dentry);
 	if (error)
 		goto exit_end_dirop;
@@ -5569,16 +5568,17 @@ retry_deleg:
 			   dentry, &delegated_inode);
 exit_end_dirop:
 	end_dirop(dentry);
-	iput(inode);	/* truncate the inode here */
 	if (is_delegated(&delegated_inode)) {
 		error = break_deleg_wait(&delegated_inode);
 		if (!error)
-			goto retry_deleg;
+			loop = 1;
 	}
 exit_drop_write:
 	mnt_drop_write(path.mnt);
 exit_path_put:
 	path_put(&path);
+	if (loop)
+		goto retry;
 	if (retry_estale(error, lookup_flags)) {
 		lookup_flags |= LOOKUP_REVAL;
 		goto retry;
--