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 C5B6027A462; Thu, 15 Jan 2026 17:39:49 +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=1768498789; cv=none; b=lAnMTG0tGALHvdiDnkaxLutg3us7BiUWSqJcLlL8ObORZpmwzuQ1pCJdVXvyDtDUW4VMndntI7xl0hN8AEWY4f/2jeI1Y65oTBHm+fDjj4E2a+8KJUSZv4PdWW1UJz2EShZG4HNGWMxhwQ4Dm75Ko0z3Sm2dsbVUNEocoeq6gJU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768498789; c=relaxed/simple; bh=LkvJHMO5tsJf5+1OUBz+rXAlfaVNh/jaAsPbPBAtxDc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=sPu2A731iNWL06nHg7WU2Z2RECqWFHSjNrEQpJ/LGFOgfsNAS6dFO9RFxYujifhEgOpVG5VYux0s94/XUTZ5MI/9SEMkJXTZFHED2/F87HZ29Te2sWyIETOXmFHLfNrCcjbQCGb0xOREuTCP/eLzV4RmTQQ7P+wVTjtYN0LQCTI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=MGczjbq0; 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="MGczjbq0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0D11CC19422; Thu, 15 Jan 2026 17:39:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1768498789; bh=LkvJHMO5tsJf5+1OUBz+rXAlfaVNh/jaAsPbPBAtxDc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MGczjbq0M4iFeswvSzJYV+S95/RwNdlwP2plC6iThCHljokY79I/qMeS62/n2RGN6 Hvq1aP1N9FXjm1zVyTx72hJSBcv/AxPuYhi05zsjBwtnyDQG76uaJiKDKnI6Hs0hD0 H+dz+rNHdf1qRHH36395FA14aOrRqAJrJ/HDmi4g= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, =?UTF-8?q?Michal=20R=C3=A1bek?= , Tomas Henzl , Changhui Zhong , "Ewan D. Milne" , John Meneghini , "Martin K. Petersen" , Sasha Levin Subject: [PATCH 5.15 554/554] scsi: sg: Fix occasional bogus elapsed time that exceeds timeout Date: Thu, 15 Jan 2026 17:50:20 +0100 Message-ID: <20260115164306.382356079@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260115164246.225995385@linuxfoundation.org> References: <20260115164246.225995385@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Michal Rábek [ Upstream commit 0e1677654259a2f3ccf728de1edde922a3c4ba57 ] A race condition was found in sg_proc_debug_helper(). It was observed on a system using an IBM LTO-9 SAS Tape Drive (ULTRIUM-TD9) and monitoring /proc/scsi/sg/debug every second. A very large elapsed time would sometimes appear. This is caused by two race conditions. We reproduced the issue with an IBM ULTRIUM-HH9 tape drive on an x86_64 architecture. A patched kernel was built, and the race condition could not be observed anymore after the application of this patch. A reproducer C program utilising the scsi_debug module was also built by Changhui Zhong and can be viewed here: https://github.com/MichaelRabek/linux-tests/blob/master/drivers/scsi/sg/sg_race_trigger.c The first race happens between the reading of hp->duration in sg_proc_debug_helper() and request completion in sg_rq_end_io(). The hp->duration member variable may hold either of two types of information: #1 - The start time of the request. This value is present while the request is not yet finished. #2 - The total execution time of the request (end_time - start_time). If sg_proc_debug_helper() executes *after* the value of hp->duration was changed from #1 to #2, but *before* srp->done is set to 1 in sg_rq_end_io(), a fresh timestamp is taken in the else branch, and the elapsed time (value type #2) is subtracted from a timestamp, which cannot yield a valid elapsed time (which is a type #2 value as well). To fix this issue, the value of hp->duration must change under the protection of the sfp->rq_list_lock in sg_rq_end_io(). Since sg_proc_debug_helper() takes this read lock, the change to srp->done and srp->header.duration will happen atomically from the perspective of sg_proc_debug_helper() and the race condition is thus eliminated. The second race condition happens between sg_proc_debug_helper() and sg_new_write(). Even though hp->duration is set to the current time stamp in sg_add_request() under the write lock's protection, it gets overwritten by a call to get_sg_io_hdr(), which calls copy_from_user() to copy struct sg_io_hdr from userspace into kernel space. hp->duration is set to the start time again in sg_common_write(). If sg_proc_debug_helper() is called between these two calls, an arbitrary value set by userspace (usually zero) is used to compute the elapsed time. To fix this issue, hp->duration must be set to the current timestamp again after get_sg_io_hdr() returns successfully. A small race window still exists between get_sg_io_hdr() and setting hp->duration, but this window is only a few instructions wide and does not result in observable issues in practice, as confirmed by testing. Additionally, we fix the format specifier from %d to %u for printing unsigned int values in sg_proc_debug_helper(). Signed-off-by: Michal Rábek Suggested-by: Tomas Henzl Tested-by: Changhui Zhong Reviewed-by: Ewan D. Milne Reviewed-by: John Meneghini Reviewed-by: Tomas Henzl Link: https://patch.msgid.link/20251212160900.64924-1-mrabek@redhat.com Signed-off-by: Martin K. Petersen Signed-off-by: Sasha Levin --- drivers/scsi/sg.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c index 4d54f2697bb4e..d74bb7b42de89 100644 --- a/drivers/scsi/sg.c +++ b/drivers/scsi/sg.c @@ -736,6 +736,8 @@ sg_new_write(Sg_fd *sfp, struct file *file, const char __user *buf, sg_remove_request(sfp, srp); return -EFAULT; } + hp->duration = jiffies_to_msecs(jiffies); + if (hp->interface_id != 'S') { sg_remove_request(sfp, srp); return -ENOSYS; @@ -821,7 +823,6 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp, return -ENODEV; } - hp->duration = jiffies_to_msecs(jiffies); if (hp->interface_id != '\0' && /* v3 (or later) interface */ (SG_FLAG_Q_AT_TAIL & hp->flags)) at_head = 0; @@ -1343,9 +1344,6 @@ sg_rq_end_io(struct request *rq, blk_status_t status) "sg_cmd_done: pack_id=%d, res=0x%x\n", srp->header.pack_id, result)); srp->header.resid = resid; - ms = jiffies_to_msecs(jiffies); - srp->header.duration = (ms > srp->header.duration) ? - (ms - srp->header.duration) : 0; if (0 != result) { struct scsi_sense_hdr sshdr; @@ -1395,6 +1393,9 @@ sg_rq_end_io(struct request *rq, blk_status_t status) done = 0; } srp->done = done; + ms = jiffies_to_msecs(jiffies); + srp->header.duration = (ms > srp->header.duration) ? + (ms - srp->header.duration) : 0; write_unlock_irqrestore(&sfp->rq_list_lock, iflags); if (likely(done)) { @@ -2523,6 +2524,7 @@ static void sg_proc_debug_helper(struct seq_file *s, Sg_device * sdp) const sg_io_hdr_t *hp; const char * cp; unsigned int ms; + unsigned int duration; k = 0; list_for_each_entry(fp, &sdp->sfds, sfd_siblings) { @@ -2560,13 +2562,17 @@ static void sg_proc_debug_helper(struct seq_file *s, Sg_device * sdp) seq_printf(s, " id=%d blen=%d", srp->header.pack_id, blen); if (srp->done) - seq_printf(s, " dur=%d", hp->duration); + seq_printf(s, " dur=%u", hp->duration); else { ms = jiffies_to_msecs(jiffies); - seq_printf(s, " t_o/elap=%d/%d", + duration = READ_ONCE(hp->duration); + if (duration) + duration = (ms > duration ? + ms - duration : 0); + seq_printf(s, " t_o/elap=%u/%u", (new_interface ? hp->timeout : jiffies_to_msecs(fp->timeout)), - (ms > hp->duration ? ms - hp->duration : 0)); + duration); } seq_printf(s, "ms sgat=%d op=0x%02x\n", usg, (int) srp->data.cmd_opcode); -- 2.51.0