Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0D26BC433FE for ; Fri, 17 Dec 2021 11:57:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235773AbhLQL5i (ORCPT ); Fri, 17 Dec 2021 06:57:38 -0500 Received: from dfw.source.kernel.org ([139.178.84.217]:52486 "EHLO dfw.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229742AbhLQL5g (ORCPT ); Fri, 17 Dec 2021 06:57:36 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 3D48D62156; Fri, 17 Dec 2021 11:57:36 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1C911C36AE5; Fri, 17 Dec 2021 11:57:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1639742255; bh=c6Vt/mqAoytgxRlY0EVJ39v8sl6iHxhWoqby1+a7sdA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Shvljr+rmCn+Ab1sQuudUyuD2nJRFzgvZ4xwWoUtkMlK+GCjrAf+v02m3MmCN6G+y FVxL4V3WuDD4dkmiq66YNVCRePIIv5LBTL/VnE5NnR/w5E/e0pBWPDRh2Y827MkQYt sQei/NcOhhAisUSQN+tQN734zkwpIPCo1Hxrp/NY= Date: Fri, 17 Dec 2021 12:57:33 +0100 From: Greg Kroah-Hartman To: Vincent Pelletier Cc: Felipe Balbi , Jens Axboe , Salah Triki , Dean Anderson , Andrew Gabbasov , Wesley Cheng , USB list , Linux Kernel Mailing List Subject: Re: [PATCH] usb: gadget: f_fs: Clear ffs_eventfd in ffs_data_reset. Message-ID: References: <96948a63d1a33da63b4f226e89ea90d21e9b0f82.1639528369.git.plr.vincent@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 17, 2021 at 08:29:54PM +0900, Vincent Pelletier wrote: > On Fri, Dec 17, 2021 at 6:51 PM Greg Kroah-Hartman > wrote: > > > > On Wed, Dec 15, 2021 at 12:32:49AM +0000, Vincent Pelletier wrote: > > > ffs_data_reset is called from both ffs_fs_kill_sb and ffs_ep0_release, so > > > it ends up being called twice when userland closes ep0 and then unmounts > > > f_fs. If userland provided an eventfd along with function's USB > > > descriptors, ffs_data_clear (via ffs_data_reset) ends up calling > > > eventfd_ctx_put as many times, causing a refcount underflow warning > > > (as of 5.15 at least). NULL-ify ffs_eventfd to prevent these extraneous > > > eventfd_ctx_put calls. > > > > > > For completeness, ffs_data_clear actually ends up being called thrice, the > > > last call being before the whole ffs structure gets freed, so when this > > > specific sequence happens there is a second underflow happening (but not > > > being reported): > > > > > > /sys/kernel/debug/tracing# modprobe usb_f_fs > > > /sys/kernel/debug/tracing# echo ffs_data_clear > set_ftrace_filter > > > /sys/kernel/debug/tracing# echo function > current_tracer > > > /sys/kernel/debug/tracing# echo 1 > tracing_on > > > (setup gadget, run and kill function userland process, teardown gadget) > > > /sys/kernel/debug/tracing# echo 0 > tracing_on > > > /sys/kernel/debug/tracing# cat trace > > > # tracer: function > > > # > > > # entries-in-buffer/entries-written: 3/3 #P:1 > > > # > > > # _-----=> irqs-off > > > # / _----=> need-resched > > > # | / _---=> hardirq/softirq > > > # || / _--=> preempt-depth > > > # ||| / _-=> migrate-disable > > > # |||| / delay > > > # TASK-PID CPU# ||||| TIMESTAMP FUNCTION > > > # | | | ||||| | | > > > smartcard-openp-436 [000] ..... 1946.208786: ffs_data_clear <-ffs_data_closed > > > smartcard-openp-431 [000] ..... 1946.279147: ffs_data_clear <-ffs_data_closed > > > smartcard-openp-431 [000] .n... 1946.905512: ffs_data_clear <-ffs_data_put > > > > > > Warning output corresponding to above trace: > > > [ 1946.284139] WARNING: CPU: 0 PID: 431 at lib/refcount.c:28 refcount_warn_saturate+0x110/0x15c > > > [ 1946.293094] refcount_t: underflow; use-after-free. > > > [ 1946.298164] Modules linked in: usb_f_ncm(E) u_ether(E) usb_f_fs(E) hci_uart(E) btqca(E) btrtl(E) btbcm(E) btintel(E) bluetooth(E) nls_ascii(E) nls_cp437(E) vfat(E) fat(E) bcm2835_v4l2(CE) bcm2835_mmal_vchiq(CE) videobuf2_vmalloc(E) videobuf2_memops(E) sha512_generic(E) videobuf2_v4l2(E) sha512_arm(E) videobuf2_common(E) videodev(E) cpufreq_dt(E) snd_bcm2835(CE) brcmfmac(E) mc(E) vc4(E) ctr(E) brcmutil(E) snd_soc_core(E) snd_pcm_dmaengine(E) drbg(E) snd_pcm(E) snd_timer(E) snd(E) soundcore(E) drm_kms_helper(E) cec(E) ansi_cprng(E) rc_core(E) syscopyarea(E) raspberrypi_cpufreq(E) sysfillrect(E) sysimgblt(E) cfg80211(E) max17040_battery(OE) raspberrypi_hwmon(E) fb_sys_fops(E) regmap_i2c(E) ecdh_generic(E) rfkill(E) ecc(E) bcm2835_rng(E) rng_core(E) vchiq(CE) leds_gpio(E) libcomposite(E) fuse(E) configfs(E) ip_tables(E) x_tables(E) autofs4(E) ext4(E) crc16(E) mbcache(E) jbd2(E) crc32c_generic(E) sdhci_iproc(E) sdhci_pltfm(E) sdhci(E) > > > [ 1946.399633] CPU: 0 PID: 431 Comm: smartcard-openp Tainted: G C OE 5.15.0-1-rpi #1 Debian 5.15.3-1 > > > [ 1946.417950] Hardware name: BCM2835 > > > [ 1946.425442] Backtrace: > > > [ 1946.432048] [] (dump_backtrace) from [] (show_stack+0x20/0x24) > > > [ 1946.448226] r7:00000009 r6:0000001c r5:c04a948c r4:c0a64e2c > > > [ 1946.458412] [] (show_stack) from [] (dump_stack+0x28/0x30) > > > [ 1946.470380] [] (dump_stack) from [] (__warn+0xe8/0x154) > > > [ 1946.482067] r5:c04a948c r4:c0a71dc8 > > > [ 1946.490184] [] (__warn) from [] (warn_slowpath_fmt+0xa0/0xe4) > > > [ 1946.506758] r7:00000009 r6:0000001c r5:c0a71dc8 r4:c0a71e04 > > > [ 1946.517070] [] (warn_slowpath_fmt) from [] (refcount_warn_saturate+0x110/0x15c) > > > [ 1946.535309] r8:c0100224 r7:c0dfcb84 r6:ffffffff r5:c3b84c00 r4:c24a17c0 > > > [ 1946.546708] [] (refcount_warn_saturate) from [] (eventfd_ctx_put+0x48/0x74) > > > [ 1946.564476] [] (eventfd_ctx_put) from [] (ffs_data_clear+0xd0/0x118 [usb_f_fs]) > > > [ 1946.582664] r5:c3b84c00 r4:c2695b00 > > > [ 1946.590668] [] (ffs_data_clear [usb_f_fs]) from [] (ffs_data_closed+0x9c/0x150 [usb_f_fs]) > > > [ 1946.609608] r5:bf54d014 r4:c2695b00 > > > [ 1946.617522] [] (ffs_data_closed [usb_f_fs]) from [] (ffs_fs_kill_sb+0x2c/0x30 [usb_f_fs]) > > > [ 1946.636217] r7:c0dfcb84 r6:c3a12260 r5:bf54d014 r4:c229f000 > > > [ 1946.646273] [] (ffs_fs_kill_sb [usb_f_fs]) from [] (deactivate_locked_super+0x54/0x9c) > > > [ 1946.664893] r5:bf54d014 r4:c229f000 > > > [ 1946.672921] [] (deactivate_locked_super) from [] (deactivate_super+0x60/0x64) > > > [ 1946.690722] r5:c2a09000 r4:c229f000 > > > [ 1946.698706] [] (deactivate_super) from [] (cleanup_mnt+0xe4/0x14c) > > > [ 1946.715553] r5:c2a09000 r4:00000000 > > > [ 1946.723528] [] (cleanup_mnt) from [] (__cleanup_mnt+0x1c/0x20) > > > [ 1946.739922] r7:c0dfcb84 r6:c3a12260 r5:c3a126fc r4:00000000 > > > [ 1946.750088] [] (__cleanup_mnt) from [] (task_work_run+0x84/0xb8) > > > [ 1946.766602] [] (task_work_run) from [] (do_work_pending+0x470/0x56c) > > > [ 1946.783540] r7:5ac3c35a r6:c0d0424c r5:c200bfb0 r4:c200a000 > > > [ 1946.793614] [] (do_work_pending) from [] (slow_work_pending+0xc/0x20) > > > [ 1946.810553] Exception stack(0xc200bfb0 to 0xc200bff8) > > > [ 1946.820129] bfa0: 00000000 00000000 000000aa b5e21430 > > > [ 1946.837104] bfc0: bef867a0 00000001 bef86840 00000034 bef86838 bef86790 bef86794 bef867a0 > > > [ 1946.854125] bfe0: 00000000 bef86798 b67b7a1c b6d626a4 60000010 b5a23760 > > > [ 1946.865335] r10:00000000 r9:c200a000 r8:c0100224 r7:00000034 r6:bef86840 r5:00000001 > > > [ 1946.881914] r4:bef867a0 > > > [ 1946.888793] ---[ end trace 7387f2a9725b28d0 ]--- > > > > > > Signed-off-by: Vincent Pelletier > > > --- > > > drivers/usb/gadget/function/f_fs.c | 1 + > > > 1 file changed, 1 insertion(+) > > > > > > diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c > > > index e20c19a0f106..437141a11ec6 100644 > > > --- a/drivers/usb/gadget/function/f_fs.c > > > +++ b/drivers/usb/gadget/function/f_fs.c > > > @@ -1791,6 +1791,7 @@ static void ffs_data_reset(struct ffs_data *ffs) > > > ffs_data_clear(ffs); > > > > > > ffs->epfiles = NULL; > > > + ffs->ffs_eventfd = NULL; > > > > Shouldn't this be happening in ffs_data_clear() instead? After the call > > to eventfd_ctx_put() as that is when the file descriptor is properly > > dropped. > > This was my initial intent while debugging, but when preparing this > submission I realised epfiles is in the same boat, and > ffs_data_reset is where it is getting set to NULL. > So I followed the pattern. > > If preferred, I can move both to ffs_data_clear, as I think it would > make the code more obviously correct (...and it may have made > this bug more obvious and maybe avoided it entirely). Both should be moved there, that is the correct thing to do. thanks, greg k-h