From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DCE588F77; Wed, 20 Nov 2024 12:32:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732105975; cv=none; b=JyHB4C2ppTW3xM2fmZbakxpLwMItC0PYOtlSNnU7dm9HSPyyWtdGgoz7XkvAsr/mMxpk1FAUSLWnKsX/2K1MlqqU/XgVd3v87mG26szi8Gvnpnzw6v8faRUXkc3bOx6WsxZ6d32G7TGxvUNdMV2DEBzF1OcHaHdwaJmbz9sGzvg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732105975; c=relaxed/simple; bh=BORz0CF2IQbmXcz7O43m7nZi39ZyC2WsbFBh0jgAF0Q=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=cJusLqmWlZ430jL09ALU0douVZ3M6Adf/Zu4uaZQy5JgOx2ymv3B+d0+tjg7jEw9rOjQ12xSu/a6EKWrdr30XdwKCXMEHTX0ZdwdLWYNZsQnynqBSVbs4IuULSO2k4CkRLnTUR7cdfNNhOQw4hk6WeuAXBMdeTzSJ4iNpcuLPwE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=ifki3lrh; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="ifki3lrh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 65C67C4CECD; Wed, 20 Nov 2024 12:32:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1732105974; bh=BORz0CF2IQbmXcz7O43m7nZi39ZyC2WsbFBh0jgAF0Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ifki3lrhQlZVPwe2jnQyj376Q5qQ+8rXgBboUtAMtC4UCWqVr2H17dMRQbS/v4gvJ ls8/EVH2agddzteywUb0iuAuWFdE7Ks5lnReoSNK+GepmfORFLrS+4LpZFeYf7ZaUD dSfPyxbOHZk5KzMmThPE9ZoLc99l6K671GQhDOZo= Date: Wed, 20 Nov 2024 13:32:29 +0100 From: Greg KH To: "Liam R. Howlett" Cc: stable@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Lorenzo Stoakes , Jann Horn , syzbot+bc6bfc25a68b7a020ee1@syzkaller.appspotmail.com, Vlastimil Babka Subject: Re: [PATCH 6.12.y v2] mm/mmap: fix __mmap_region() error handling in rare merge failure case Message-ID: <2024112019-skating-goofball-d2be@gregkh> References: <20241119175945.2600945-1-Liam.Howlett@oracle.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241119175945.2600945-1-Liam.Howlett@oracle.com> On Tue, Nov 19, 2024 at 12:59:45PM -0500, Liam R. Howlett wrote: > From: "Liam R. Howlett" > > The mmap_region() function tries to install a new vma, which requires a > pre-allocation for the maple tree write due to the complex locking > scenarios involved. > > Recent efforts to simplify the error recovery required the relocation of > the preallocation of the maple tree nodes (via vma_iter_prealloc() > calling mas_preallocate()) higher in the function. > > The relocation of the preallocation meant that, if there was a file > associated with the vma and the driver call (mmap_file()) modified the > vma flags, then a new merge of the new vma with existing vmas is > attempted. > > During the attempt to merge the existing vma with the new vma, the vma > iterator is used - the same iterator that would be used for the next > write attempt to the tree. In the event of needing a further allocation > and if the new allocations fails, the vma iterator (and contained maple > state) will cleaned up, including freeing all previous allocations and > will be reset internally. > > Upon returning to the __mmap_region() function, the error is available > in the vma_merge_struct and can be used to detect the -ENOMEM status. > > Hitting an -ENOMEM scenario after the driver callback leaves the system > in a state that undoing the mapping is worse than continuing by dipping > into the reserve. > > A preallocation should be performed in the case of an -ENOMEM and the > allocations were lost during the failure scenario. The __GFP_NOFAIL > flag is used in the allocation to ensure the allocation succeeds after > implicitly telling the driver that the mapping was happening. > > The range is already set in the vma_iter_store() call below, so it is > not necessary and is dropped. > > Reported-by: syzbot+bc6bfc25a68b7a020ee1@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/x/log.txt?x=17b0ace8580000 > Fixes: 5de195060b2e2 ("mm: resolve faulty mmap_region() error path behaviour") > Signed-off-by: Liam R. Howlett > Reviewed-by: Vlastimil Babka > Reviewed-by: Lorenzo Stoakes > Cc: Jann Horn > Cc: > --- > mm/mmap.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > Changes since v1: > - Don't bail out and force the allocation when the merge failure is > -ENOMEM - Thanks Lorenzo Now queued up, thanks. greg k-h