linux-kernel - Re: [syzbot] [hardening?] [mm?] BUG: bad usercopy in vfs

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Message-ID: <zv5u3q3m7t5yehblaqnrcz2k73yozpx7nn5mvbkedrzw2jaowf@soiirioxlfbz>
Date: Wed, 5 Feb 2025 13:26:18 +0100
From: Mateusz Guzik <mjguzik@...il.com>
To: syzbot <syzbot+48a99e426f29859818c0@...kaller.appspotmail.com>
Cc: akpm@...ux-foundation.org, brauner@...nel.org, gustavoars@...nel.org, 
	kees@...nel.org, linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, syzkaller-bugs@...glegroups.com, tytso@....edu
Subject: Re: [syzbot] [hardening?] [mm?] BUG: bad usercopy in vfs_readlink

On Tue, Feb 04, 2025 at 01:46:28AM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    69b8923f5003 Merge tag 'for-linus-6.14-ofs4' of git://git...
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1258aeb0580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=57ab43c279fa614d
> dashboard link: https://syzkaller.appspot.com/bug?extid=48a99e426f29859818c0
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15825724580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1658aeb0580000
> 

#syz test  upstream  master

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 7c54ae5fcbd4..30cff983e601 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5010,7 +5010,7 @@ struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
 			nd_terminate_link(ei->i_data, inode->i_size,
 				sizeof(ei->i_data) - 1);
 			inode_set_cached_link(inode, (char *)ei->i_data,
-					      inode->i_size);
+					      strlen((char *)ei->i_data));
 		} else {
 			inode->i_op = &ext4_symlink_inode_operations;
 		}