From nobody Thu Apr 9 16:32:34 2026 Received: from mail-oo1-f69.google.com (mail-oo1-f69.google.com [209.85.161.69]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1113637473B for ; Sat, 7 Mar 2026 08:24:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.161.69 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772871864; cv=none; b=Kc/54iDAQ9vGdlKCKpj6d6GrsW/tmk/RXFnu38Ym5j5w//nOg14gYKGkzCARxCrjDB6OVmjOH/JIzo8H33EL2ZZqOBal2RMFtP1YcHxtcZKEAZjlKuN3J1zLt7IAmcEMfz/5SI026NKn4/ZrNixzzkc0uMj7G8VAfG7spj9zqa4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772871864; c=relaxed/simple; bh=8V2ouupKO27QzUIKR2mUk4uDkcJ6G6b7pYWhHwuqz9Y=; h=MIME-Version:Date:In-Reply-To:Message-ID:Subject:From:To: Content-Type; b=aj1PFMeoiq6YAFy8tgVz5F8MUts2b5ApKOwQ8MhK3yOUQ1eHXs3f5zbXOK7CPIwWcKHTgws3dfzGOuWURgBmtWXiPft/NSiw+qTSk2RYPkOo16Ch/F5GFIR71rIWfZg4EQdbNYP6GQtHK9XEtAa81rGpBOlYmqCxjVKWksgEJXs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com; arc=none smtp.client-ip=209.85.161.69 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com Received: by mail-oo1-f69.google.com with SMTP id 006d021491bc7-67995e1ecacso150766493eaf.0 for ; Sat, 07 Mar 2026 00:24:22 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1772871862; x=1773476662; h=to:from:subject:message-id:in-reply-to:date:mime-version :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=fl4QjAHkRwlN4OTg0LVkSWfkuryJkKq+0h24nl2+QQM=; b=SrZdqI2b+rUH0DkrJsOyW5C0K9KwohJv4U0YKGkzldgi8jcuQCcKoCx7llQiuPfCNG K4jE5x50NlQwNg4+mDEzkCcIXR7pCnttv12RCaIcni2lPsTiLFGpPYK7NTJkdU0t5jQp 7FtuLWH3/XporBPhDRrBhNGUiY4SALZhkXxmDvdOkg6rqReivluvpAr0I3QTNn8eYZSC Zq09XyhauYgOTqk+JCd6XvaHIZUaY/5kmr2VxggQ8a6SkiKmi4PiJnYSFDhk8o1nm+fx gXfbFB6PSzYQw768SX2mdeISLHPUG/BhZhfajfePXN1ZoJHPs9IPdSA8FcxflBjP4RXD g25Q== X-Gm-Message-State: AOJu0Yy3CipvcLgZ8YJh4y7hUrVtwepcKMhTX9QquN9GBeTTkeMGNgNw qjBdysmMaNYGXi93K/UJzBY0Chw2cKjL2onDWY69Kdk+aGN74cda0aTLRdbVEpYeIG/3X28BMey sVlLoyVgtPCx33evVLtwARSHqPaGQUAaVMhoQWcdLnWGCWCvH74qR8hZFG7c= Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Received: by 2002:a05:6820:1511:b0:679:f16a:622c with SMTP id 006d021491bc7-67b9bca1ff5mr3231365eaf.29.1772871862119; Sat, 07 Mar 2026 00:24:22 -0800 (PST) Date: Sat, 07 Mar 2026 00:24:22 -0800 In-Reply-To: <69aa75e2.050a0220.13f275.000f.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <69abe0b6.050a0220.13f275.0044.GAE@google.com> Subject: Forwarded: [PATCH] netfs: Fix kernel BUG in netfs_limit_iter() for ITER_KVEC iterators From: syzbot To: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" For archival purposes, forwarding an incoming command email to linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com. *** Subject: [PATCH] netfs: Fix kernel BUG in netfs_limit_iter() for ITER_KVEC = iterators Author: kartikey406@gmail.com #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git= master When a process crashes and the kernel writes a core dump to a 9P filesystem, __kernel_write() creates an ITER_KVEC iterator. This iterator reaches netfs_limit_iter() via netfs_unbuffered_write(), which only handles ITER_FOLIOQ, ITER_BVEC and ITER_XARRAY iterator types, hitting the BUG() for any other type. Fix this by adding netfs_limit_kvec() following the same pattern as netfs_limit_bvec(), since both kvec and bvec are simple segment arrays with pointer and length fields. Dispatch it from netfs_limit_iter() when the iterator type is ITER_KVEC. Fixes: cae932d3aee5 ("netfs: Add func to calculate pagecount/size-limited s= pan of an iterator") Reported-by: syzbot+9c058f0d63475adc97fd@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D9c058f0d63475adc97fd Signed-off-by: Deepanshu Kartikey --- fs/netfs/iterator.c | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c index 72a435e5fc6d..154a14bb2d7f 100644 --- a/fs/netfs/iterator.c +++ b/fs/netfs/iterator.c @@ -142,6 +142,47 @@ static size_t netfs_limit_bvec(const struct iov_iter *= iter, size_t start_offset, return min(span, max_size); } =20 +/* + * Select the span of a kvec iterator we're going to use. Limit it by both + * maximum size and maximum number of segments. Returns the size of the s= pan + * in bytes. + */ +static size_t netfs_limit_kvec(const struct iov_iter *iter, size_t start_o= ffset, + size_t max_size, size_t max_segs) +{ + const struct kvec *kvecs =3D iter->kvec; + unsigned int nkv =3D iter->nr_segs, ix =3D 0, nsegs =3D 0; + size_t len, span =3D 0, n =3D iter->count; + size_t skip =3D iter->iov_offset + start_offset; + + if (WARN_ON(!iov_iter_is_kvec(iter)) || + WARN_ON(start_offset > n) || + n =3D=3D 0) + return 0; + + while (n && ix < nkv && skip) { + len =3D kvecs[ix].iov_len; + if (skip < len) + break; + skip -=3D len; + n -=3D len; + ix++; + } + + while (n && ix < nkv) { + len =3D min3(n, kvecs[ix].iov_len - skip, max_size); + span +=3D len; + nsegs++; + ix++; + if (span >=3D max_size || nsegs >=3D max_segs) + break; + skip =3D 0; + n -=3D len; + } + + return min(span, max_size); +} + /* * Select the span of an xarray iterator we're going to use. Limit it by = both * maximum size and maximum number of segments. It is assumed that segmen= ts @@ -245,6 +286,8 @@ size_t netfs_limit_iter(const struct iov_iter *iter, si= ze_t start_offset, return netfs_limit_bvec(iter, start_offset, max_size, max_segs); if (iov_iter_is_xarray(iter)) return netfs_limit_xarray(iter, start_offset, max_size, max_segs); + if (iov_iter_is_kvec(iter)) + return netfs_limit_kvec(iter, start_offset, max_size, max_segs); BUG(); } EXPORT_SYMBOL(netfs_limit_iter); --=20 2.43.0