From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 2D64D606A32E for ; Wed, 28 Oct 2026 15:04:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=ii2Cv1I1 Received: by kanga.kvack.org (Postfix) id C3A726B05BC; Wed, 28 Oct 2026 11:04:44 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C11F06B05BE; Wed, 28 Oct 2026 11:04:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AFE406B05BC; Wed, 28 Oct 2026 11:04:44 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 7FF886B05BC for ; Wed, 28 Oct 2026 11:04:44 -0400 (EDT) Received: from smtpin23.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay09.hostedemail.com (Postfix) with ESMTP id E91818012E for ; Wed, 28 Oct 2026 15:04:43 +0000 (UTC) X-FDA: 85372356846.23.7AEDAFF Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf01.hostedemail.com (Postfix) with ESMTP id 4B87E40005 for ; Wed, 28 Oct 2026 15:04:42 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ii2Cv1I1; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf01.hostedemail.com: domain of sashiko-bot@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=sashiko-bot@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793199882; h=from:from:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=mSdqxz6Q37ONxr+q5PLgX5Mx5sgsbL1ZlDMhRwJ4tls=; b=xQi3AwNApXdwGp0/zHbXR3Xr/v0QnmIAX7Ttbq8zeiSXSS4gTBbkFZrDqROMoMWG/Lw0+F w8MOIhwp9knJvFqzRnxFXUnnvDqwfW7PU8dGhgGWRhBDfOVuHRia7s3IqEE9lBeO4YjyiF NjiWpxEyOfs4B4IveQadBqdRVMpYDB8= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ii2Cv1I1; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf01.hostedemail.com: domain of sashiko-bot@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=sashiko-bot@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793199882; b=izpp8eaMtA6TcusClnDxlmAcMB9QJsVCDUzu8K+Y9zLmWJMkpn2dFtsTbeShrSS9H4dRHq QUDR+UMmhhY8pSY5tLTbZ8Vnnrlbam9ZlpPpU3z5vX9ugaJrFheeW+rh0TTqvoPZoeIwcT BaAZ6kVEpVYD/YyLAhaZ6o5S5J6PgHI= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 833BF60252; Wed, 28 Oct 2026 15:04:41 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AC7631F01829; Wed, 28 Oct 2026 15:04:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793199881; bh=mSdqxz6Q37ONxr+q5PLgX5Mx5sgsbL1ZlDMhRwJ4tls=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=ii2Cv1I1mFw6z0jUk6ND3vI1KQsc+cPLiCIZMvKnAo54Gp0s/gplwdGsTCOINjF3m Vyp8TPUP1c89LMrtNfl1SSCyLKR8iCzMdClXf8Ag22Q466Srn6wp0pPBEPe1niet9S ltmp6epcmx5o/iHtRObx0gat20oSI3vbNsnbdjdF1arYD08Zmh3aUxS6DVRKuWcEhE +D3p7ka5Cqbc2R7/WvOlKFR5jK2qoxxu/WaG77pXfVBFw+gw6l11JjB/aHP5om3QIg XPjWzyvY1HOBKSJdOvSWDFjmd3ugT+ApaWExa7poGt1jjmuxkJPlMjdXVPIc7LG6HW WCOxu4Wy9nCCA== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH v3 7/8] dma-buf: transfer memcg charges via DMA_BUF_IOCTL_XFER_CHARGE Reply-To: sashiko-reviews@lists.linux.dev To: "Albert Esteve" , "Tejun Heo" , "Johannes Weiner" , =?utf-8?b?TWljaGFsIEtvdXRuw70=?= , "Jonathan Corbet" , "Shuah Khan" , "Sumit Semwal" , =?utf-8?b?Q2hyaXN0aWFuIEvDtm5pZw==?= , "Michal Hocko" , "Roman Gushchin" , "Shakeel Butt" , "Muchun Song" , "Andrew Morton" , "Benjamin Gaignard" , "Brian Starkey" , "John Stultz" , "T.J. Mercier" , "Christian Brauner" , "Paul Moore" , "James Morris" , "Serge E. Hallyn" , "Stephen Smalley" , "Shuah Khan" , "Randy Dunlap" , =?utf-8?b?T25kcmVqIE1vc27DocSNZWs=?= , "Jens Wiklander" , "Sumit Garg" Cc: dri-devel@lists.freedesktop.org, linux-mm@kvack.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, op-tee@lists.trustedfirmware.org, echanude@redhat.com, mripard@kernel.org, media-ci@linuxtv.org In-Reply-To: <20261027-v2_20230123_tjmercier_google_com-v3-7-78d2c4cb8647@redhat.com> References: <20261027-v2_20230123_tjmercier_google_com-v3-0-78d2c4cb8647@redhat.com> <20261027-v2_20230123_tjmercier_google_com-v3-7-78d2c4cb8647@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Wed, 28 Oct 2026 15:04:39 +0000 X-Rspamd-Queue-Id: 4B87E40005 X-Stat-Signature: j885cp83zohhcwe9thmrdsodkjukphkn X-Rspamd-Server: rspam06 X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793199882-629686 X-HE-Meta: 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 /o7ac1hf 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 X-Archived-By: Thank you for your contribution! Sashiko AI review found 3 potential issue(= s) to consider: - [High] dma-buf: unprivileged cgroup escape and OOM via dma_buf_xfer_charg= e() - [High] dma-buf: race in mem_cgroup_transfer_dmabuf_charge() double-charge= s memcg - [Medium] dma-buf: broken disabled-memcg handling in dma_buf_xfer_charge() -- commit 1660729e62b15fd915c69f26225530bd5ae30ce0 Author: Albert Esteve dma-buf: transfer memcg charges via DMA_BUF_IOCTL_XFER_CHARGE This commit adds DMA_BUF_IOCTL_XFER_CHARGE to allow transferring a dma-buf's memory cgroup charge to a cgroup identified by a cgroupfd or pidfd after allocation. It also introduces a memcg_account flag in dma_buf_export_info = for exporters to opt in to memcg accounting, enabling it for the system heap. > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > index f31f49ebd0af3..07513ecedc105 100644 > --- a/drivers/dma-buf/dma-buf.c > +++ b/drivers/dma-buf/dma-buf.c > @@ -540,6 +540,45 @@ static long dma_buf_import_sync_file(struct dma_buf = *dmabuf, > } > #endif > =20 > +/* Transfer a dma-buf's memcg charge; see struct dma_buf_transfer_charge= */ > +static long dma_buf_xfer_charge(struct dma_buf *dmabuf, > + const void __user *user_data) > +{ > + struct dma_buf_transfer_charge arg; > + struct mem_cgroup *memcg; > + int ret =3D 0; > + > + if (copy_from_user(&arg, user_data, sizeof(arg))) > + return -EFAULT; > + > + if (!IS_ENABLED(CONFIG_MEMCG)) > + return 0; > + > + if (arg.flags !=3D 0) > + return -EINVAL; > + > + if (!dmabuf->memcg_account) > + return -EOPNOTSUPP; [Severity: Medium] When CONFIG_MEMCG is disabled, should dma_buf_xfer_charge() still validate arg.flags and dmabuf->memcg_account, or return -EOPNOTSUPP? Returning 0 before checking arg.flags !=3D 0 and !dmabuf->memcg_account cau= ses calls with invalid flags, non-accounting exporters, or invalid file descriptors to silently succeed under CONFIG_MEMCG=3Dn, while also leaving = the !CONFIG_MEMCG stubs for mem_cgroup_get_from_fd() (which returns ERR_PTR(-EOPNOTSUPP)) and mem_cgroup_transfer_dmabuf_charge() in include/linux/memcontrol.h unreachable. Also, when CONFIG_MEMCG=3Dy and cgroup_disable=3Dmemory is passed on the ke= rnel command line (so mem_cgroup_disabled() is true at runtime), mem_cgroup_get_from_fd() behaves inconsistently across its two branches: mm/memcontrol.c:mem_cgroup_get_from_fd() { cgrp =3D cgroup_get_from_fd(fd); if (!IS_ERR(cgrp)) { rcu_read_lock(); css =3D cgroup_css(cgrp, &memory_cgrp_subsys); if (!css || !css_tryget_online(css)) { rcu_read_unlock(); cgroup_put(cgrp); return ERR_PTR(-ENOENT); } ... memcg =3D get_mem_cgroup_from_mm(mm); mmput(mm); return memcg; } For a cgroupfd, cgroup_css() is NULL and it returns ERR_PTR(-ENOENT), where= as for a pidfd, get_mem_cgroup_from_mm() returns NULL rather than an ERR_PTR, = so dma_buf_xfer_charge() returns 0 for pidfds and -ENOENT for cgroupfds. > + > + memcg =3D mem_cgroup_get_from_fd(arg.charge_fd); > + if (IS_ERR(memcg)) > + return PTR_ERR(memcg); > + > + if (dmabuf->memcg =3D=3D memcg) > + goto skip_transfer; > + > + if (!mem_cgroup_transfer_dmabuf_charge(dmabuf, memcg)) { > + ret =3D -ENOMEM; > + goto skip_transfer; > + } [Severity: High] Can an unprivileged holder of a dma-buf file descriptor use dma_buf_xfer_charge() to escape its own memory cgroup limit or trigger OOM kills in another cgroup? In the call chain: dma_buf_ioctl() -> dma_buf_xfer_charge() -> mem_cgroup_get_from_fd() -> mem_cgroup_transfer_dmabuf_charge() -> mem_cgroup_reserve_dmabuf(new_memcg, GFP_KERNEL, nr_pages) -> try_charge() neither dma_buf_xfer_charge() nor mem_cgroup_get_from_fd() checks DAC or cgroup delegation/write permissions (such as inode_permission() with MAY_WR= ITE or cgroup_procs_write_permission()), capabilities, or ptrace_may_access() on either the source cgroup (dmabuf->memcg) being uncharged or the target cgroup/task (new_memcg) being charged. Because /sys/fs/cgroup directories are normally world-readable (mode 0755, = so any user can open them with O_RDONLY | O_DIRECTORY) and pidfd_open() can op= en a pidfd for PID 1 or any visible process without privilege, an unprivileged process can resolve a handle to the root cgroup or to another cgroup on the system. When SELinux is not active, security_dma_buf_charge_cgroup() and security_dma_buf_charge_task() return 0. Even with SELinux enabled, selinux_dma_buf_charge_cgroup() returns 0 when the cgroup kernfs node has no explicit security.selinux xattr set: security/selinux/hooks.c:selinux_dma_buf_charge_cgroup() { rc =3D kernfs_xattr_get(cgrp->kn, XATTR_NAME_SELINUX, NULL, 0); if (rc =3D=3D -ENODATA) return 0; } and neither hook checks permission to uncharge the existing dmabuf->memcg. = As a result, a confined client receiving a pre-charged dma-buf fd can move the charge to the root cgroup to bypass its own memory.max limit, or move the charge into a victim cgroup where mem_cgroup_reserve_dmabuf() with GFP_KERN= EL triggers direct reclaim and the memcg OOM killer. > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 7b841b9057594..3adc84fe6668d 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5786,6 +5786,47 @@ void mem_cgroup_cancel_dmabuf(struct mem_cgroup *m= emcg, unsigned int nr_pages) > refill_stock(memcg, nr_pages); > } > =20 > +/** > + * mem_cgroup_transfer_dmabuf_charge - move a dma-buf charge > + * @dmabuf: buffer to transfer charge > + * @new_memcg: target memcg; caller must hold a reference > + * > + * Transfers the charge for @dmabuf to @new_memcg and, on > + * success, stores @new_memcg in @dmabuf->memcg. > + * Returns %true on success, %false if the charge against @new_memcg > + * failed or a concurrent transfer raced on @dmabuf->memcg. > + * On failure the caller retains its reference to @new_memcg. > + */ > +bool mem_cgroup_transfer_dmabuf_charge(struct dma_buf *dmabuf, > + struct mem_cgroup *new_memcg) > +{ > + struct mem_cgroup *old_memcg =3D READ_ONCE(dmabuf->memcg); > + unsigned int nr_pages =3D PAGE_ALIGN(dmabuf->size) >> PAGE_SHIFT; > + > + if (mem_cgroup_disabled()) > + return true; > + > + if (!mem_cgroup_reserve_dmabuf(new_memcg, GFP_KERNEL, nr_pages)) > + return false; > + > + mod_memcg_state(new_memcg, MEMCG_DMABUF, nr_pages); > + > + if (cmpxchg(&dmabuf->memcg, old_memcg, new_memcg) !=3D old_memcg) { > + mod_memcg_state(new_memcg, MEMCG_DMABUF, -nr_pages); > + mem_cgroup_cancel_dmabuf(new_memcg, nr_pages); > + return false; > + } [Severity: High] What happens if two threads concurrently call DMA_BUF_IOCTL_XFER_CHARGE on = the same dma-buf? In dma_buf_xfer_charge(), dmabuf->memcg =3D=3D memcg is checked without synchronization before calling mem_cgroup_transfer_dmabuf_charge(), which t= hen re-reads old_memcg =3D READ_ONCE(dmabuf->memcg) without checking whether old_memcg =3D=3D new_memcg. If thread 1 transfers the buffer to new_memcg after thread 2 passes the dmabuf->memcg =3D=3D memcg check in dma_buf_xfer_charge() (or if both threa= ds concurrently transfer the buffer to the same new_memcg), thread 2 sees old_memcg =3D=3D new_memcg and still calls mem_cgroup_reserve_dmabuf(new_me= mcg, GFP_KERNEL, nr_pages) before uncharging old_memcg. That transiently charges 2 * nr_pages against new_memcg for the same buffer, which can trigger recla= im, memcg OOM kills, or -ENOMEM in new_memcg even though the buffer is already charged to it. In addition, old_memcg is read before mem_cgroup_reserve_dmabuf(new_memcg, GFP_KERNEL, nr_pages), which can sleep in direct reclaim. If another thread updates dmabuf->memcg while mem_cgroup_reserve_dmabuf() is sleeping, the cmpxchg(&dmabuf->memcg, old_memcg, new_memcg) fails without retrying against the updated old_memcg and returns false, which dma_buf_xfer_charge() reports to userspace as -ENOMEM even though charging new_memcg succeeded. Finally, if mem_cgroup_transfer_dmabuf_charge() is called when mem_cgroup_disabled() is true, returning true at the top without storing new_memcg in dmabuf->memcg or dropping new_memcg's reference would leak the caller's reference to new_memcg, since callers only call mem_cgroup_put() = when this function returns false. --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261027-v2_2023012= 3_tjmercier_google_com-v3-0-78d2c4cb8647@redhat.com?part=3D7