linux-kernel - Re: [syzbot] [fs?] BUG: unable to handle kernel NULL pointer dereference in filemap_read

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Message-Id: <20241117001814.1342-1-hdanton@sina.com>
Date: Sun, 17 Nov 2024 08:18:14 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+09b7d050e4806540153d@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [fs?] BUG: unable to handle kernel NULL pointer dereference in filemap_read_folio (4)

On Sat, 16 Nov 2024 15:40:29 -0800
> syzbot found the following issue on:
> 
> HEAD commit:    3022e9d00ebe Merge tag 'sched_ext-for-6.12-rc7-fixes' of g..
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=159f8ce8580000

#syz test

--- x/mm/filemap.c
+++ y/mm/filemap.c
@@ -3781,6 +3781,8 @@ static struct folio *do_read_cache_folio
 
 	if (!filler)
 		filler = mapping->a_ops->read_folio;
+	if (!filler)
+		return ERR_PTR(-EINVAL);
 repeat:
 	folio = filemap_get_folio(mapping, index);
 	if (IS_ERR(folio)) {
--