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 DCAD845C0B; Sun, 26 Oct 2025 16:05:00 +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=1761494701; cv=none; b=CSr62wCUTNzU7FYBZXTDeANpTmpY1xH5PERbSFVWgeTgqLTIVNEJzYS9m8VKdPC7lCMc455x7xDpFWwVVGOw85kd2AW083gsIHQmrb4K+BU3sbx2Xir3Fi6PjMRKDUEN0jnI5YYUdbHnx+SI5rg42+JNnXDRIfBbb1axXnla1Rw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761494701; c=relaxed/simple; bh=l7JPkliu+UAJY5jgLqKO+0m/pMNLoNR87mNscuCPqhU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ZVwcl7R94FKOADTOEJA3xYIi0iTV1FVp53wNOj+nR8gi6xZosseAearHn922EbTmWdWiuEzLGH+3W07aNhFdpZOO8TzTYJ92RlPVeprzIfnA4yuhYl7I99lUj8JB9+0FC67ZUfLhiBM9cilI4f6P74edLoysu1CiUAVVoO3jy0U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cVtW0NKe; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="cVtW0NKe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D019DC4CEE7; Sun, 26 Oct 2025 16:04:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1761494700; bh=l7JPkliu+UAJY5jgLqKO+0m/pMNLoNR87mNscuCPqhU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cVtW0NKeE9+CKIn2dxUtvyxQTcVBo2OzidnfN8htCwbPWpSB1XMuemJIcPEWAZM3b bRe0TG/rWB1cLfzjIjYD7wZyRZgR9Fj1c1uNFQWRKnPag6j7Qwwf82h7YJAdDWJ6Ab yxGHmGJ/pgobJEX/BFUsh2wqo8YGQp9I1nmjS6uNsNwj2U6RrUcwrnOgONCRvKIi2P Usva7N/bsQXopbVKo5FzJ1xPU5ROegU21mq6V4hmzKXq3VLFFYJMlSnQ8aIDZN43HX q9IlwrPhYYIw8UXDnyYDB/kXwzR87H2UCv5D2+wro75USR+JwwtiKs1JGhIuxfJnu1 EovmCwQVFBcBA== From: Sasha Levin To: stable@vger.kernel.org Cc: Jakub Acs , Jan Kara , Amir Goldstein , Miklos Szeredi , Christian Brauner , linux-unionfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Sasha Levin Subject: [PATCH 6.6.y] fs/notify: call exportfs_encode_fid with s_umount Date: Sun, 26 Oct 2025 12:04:56 -0400 Message-ID: <20251026160456.99836-1-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <2025102612-kissing-atrocious-4949@gregkh> References: <2025102612-kissing-atrocious-4949@gregkh> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jakub Acs [ Upstream commit a7c4bb43bfdc2b9f06ee9d036028ed13a83df42a ] Calling intotify_show_fdinfo() on fd watching an overlayfs inode, while the overlayfs is being unmounted, can lead to dereferencing NULL ptr. This issue was found by syzkaller. Race Condition Diagram: Thread 1 Thread 2 -------- -------- generic_shutdown_super() shrink_dcache_for_umount sb->s_root = NULL | | vfs_read() | inotify_fdinfo() | * inode get from mark * | show_mark_fhandle(m, inode) | exportfs_encode_fid(inode, ..) | ovl_encode_fh(inode, ..) | ovl_check_encode_origin(inode) | * deref i_sb->s_root * | | v fsnotify_sb_delete(sb) Which then leads to: [ 32.133461] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000006: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI [ 32.134438] KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037] [ 32.135032] CPU: 1 UID: 0 PID: 4468 Comm: systemd-coredum Not tainted 6.17.0-rc6 #22 PREEMPT(none) [ 32.143353] Call Trace: [ 32.143732] ovl_encode_fh+0xd5/0x170 [ 32.144031] exportfs_encode_inode_fh+0x12f/0x300 [ 32.144425] show_mark_fhandle+0xbe/0x1f0 [ 32.145805] inotify_fdinfo+0x226/0x2d0 [ 32.146442] inotify_show_fdinfo+0x1c5/0x350 [ 32.147168] seq_show+0x530/0x6f0 [ 32.147449] seq_read_iter+0x503/0x12a0 [ 32.148419] seq_read+0x31f/0x410 [ 32.150714] vfs_read+0x1f0/0x9e0 [ 32.152297] ksys_read+0x125/0x240 IOW ovl_check_encode_origin derefs inode->i_sb->s_root, after it was set to NULL in the unmount path. Fix it by protecting calling exportfs_encode_fid() from show_mark_fhandle() with s_umount lock. This form of fix was suggested by Amir in [1]. [1]: https://lore.kernel.org/all/CAOQ4uxhbDwhb+2Brs1UdkoF0a3NSdBAOQPNfEHjahrgoKJpLEw@mail.gmail.com/ Fixes: c45beebfde34 ("ovl: support encoding fid from inode with no alias") Signed-off-by: Jakub Acs Cc: Jan Kara Cc: Amir Goldstein Cc: Miklos Szeredi Cc: Christian Brauner Cc: linux-unionfs@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Jan Kara [ Adjust context ] Signed-off-by: Sasha Levin --- fs/notify/fdinfo.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/fs/notify/fdinfo.c b/fs/notify/fdinfo.c index 26655572975d3..1aa7de55094cd 100644 --- a/fs/notify/fdinfo.c +++ b/fs/notify/fdinfo.c @@ -17,6 +17,7 @@ #include "fanotify/fanotify.h" #include "fdinfo.h" #include "fsnotify.h" +#include "../internal.h" #if defined(CONFIG_PROC_FS) @@ -50,7 +51,12 @@ static void show_mark_fhandle(struct seq_file *m, struct inode *inode) f.handle.handle_bytes = sizeof(f.pad); size = f.handle.handle_bytes >> 2; + if (!super_trylock_shared(inode->i_sb)) + return; + ret = exportfs_encode_fid(inode, (struct fid *)f.handle.f_handle, &size); + up_read(&inode->i_sb->s_umount); + if ((ret == FILEID_INVALID) || (ret < 0)) return; -- 2.51.0