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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=K+qv0mwQ; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AAB8F6070A97; Wed, 4 Nov 2026 19:27:43 +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=K+qv0mwQ Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9BA621F000C1; Wed, 4 Nov 2026 19:27:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793820463; bh=8vwIQDZABfbDXUA4Rhtj/FFiRIzet50vFXOLtBzgPyU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=K+qv0mwQcjtL/qGdS6zLTIdv/G0RXM8xsdMjUnhgG0fNfAYk4b2pJX930sQZnPQep +LPdNInthRhEsKuQKDBplBRNncD5RXDkf1MmvrNYXt/kezR7Og4AukJlDkC+uqQdvQ 3UcyZsZ5M2SCBuJu/oEitA7gekht06is34RQC+0SGBCyvPBf2/f+wRq4YKjtHH607t u2wONuJ6/ShFerskIef6UB1DalfazMx1QVWxa/FYtYmDpi1QxRXXlAEaJ1aaOkdQFG kAOIkXKB/WNg0BuIpmEdndNkSZIlkssgbriZFcnsRM4VXunhgfFvWP2W8uGj5+pKbF w0V3MGDPqlrPQ== From: Christian Brauner To: linux-fsdevel@vger.kernel.org Cc: Linus Torvalds , Jann Horn , Josef Bacik , Chris Mason , Jeff Layton , NeilBrown , Eric Dumazet , Thomas Gleixner , Al Viro , Jonathan Corbet , Christoph Hellwig , Greg Kroah-Hartman , Joel Granados , Kees Cook , Jan Kara , Jan Kara , linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-acpi@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, linux-um@lists.infradead.org, linux-wireless@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, ntfs3@lists.linux.dev, platform-driver-x86@vger.kernel.org, coreteam@netfilter.org, kexec@lists.infradead.org, linux-pci@vger.kernel.org, linux-sound@vger.kernel.org, netfilter-devel@vger.kernel.org, dri-devel@lists.freedesktop.org, ibm-acpi-devel@lists.sourceforge.net, jfs-discussion@lists.sourceforge.net, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-cifs@vger.kernel.org, linux-fbdev@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-mm@kvack.org, linux-sh@vger.kernel.org, linux-usb@vger.kernel.org, samba-technical@lists.samba.org, sparclinux@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-doc@vger.kernel.org, linux-serial@vger.kernel.org, linux-atm-general@lists.sourceforge.net, Takashi Iwai , linux-input@vger.kernel.org, linux-raid@vger.kernel.org, linux-ext4@vger.kernel.org, linux-modules@vger.kernel.org, linux-debuggers@vger.kernel.org, "Christian Brauner (Amutable)" , Chuck Lever Subject: [PATCH RESEND v2 47/51] proc: sysctl: look at the table under sysctl_lock when creating an inode Date: Wed, 4 Nov 2026 20:27:29 +0100 Message-ID: <20261104-work-procfs-bugfixes-v2-47-021c84d852e0@kernel.org> In-Reply-To: <20261104-work-procfs-bugfixes-v2-0-021c84d852e0@kernel.org> References: <20261104-work-procfs-bugfixes-v2-0-021c84d852e0@kernel.org> X-Mailing-List: linux-debuggers@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" X-Mailer: b4 0.17-dev X-Developer-Signature: v=1; a=openpgp-sha256; l=2783; i=brauner@kernel.org; h=from:subject:message-id; bh=qNc6cmXDzjiIgH+LQmxRb8DpjTAU1o7z7wzEsOSW+y4=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWS9bmJza0sIPDqr+OtjFeG4XR03HmoLr7n57Jt/hcxie 69L4b9dO0pZGMS4GGTFFFkc2k3C5ZbzVGw2ytSAmcPKBDKEgYtTACbi187wv2hWT/9l9+XPdiy4 Mvm7x6F5LA4Csrv4Z0ak9SrWM8XotDD8M7ASkA469SZgqbzuxov6f2ekegdpRrKw1vJ3ZETYaKT yAAA= X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 Content-Transfer-Encoding: 8bit proc_sys_make_inode() checks under sysctl_lock that @head isn't being unregistered, lets go of the lock, and then reads the mode of @table and calls ->set_ownership() with @head. That's fine as long as the caller holds @head in use, which keeps unregistering from getting past that check. The next patch has a caller that only pins the memory of @head. For that one the table, and whatever the owner of the header keeps behind it, is only there for as long as nobody unregisters the header, which happens under sysctl_lock. So read the mode and set the ownership before letting go of the lock. The ->set_ownership() callbacks only look up ids in a user namespace. No functional changes. Signed-off-by: Christian Brauner (Amutable) --- fs/proc/proc_sysctl.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c index f5c9f04e8509..82024f1ea756 100644 --- a/fs/proc/proc_sysctl.c +++ b/fs/proc/proc_sysctl.c @@ -500,6 +500,7 @@ static struct inode *proc_sys_make_inode(struct super_block *sb, struct ctl_table_root *root = head->root; struct inode *inode; struct proc_inode *ei; + umode_t mode; inode = new_inode(sb); if (!inode) @@ -509,12 +510,22 @@ static struct inode *proc_sys_make_inode(struct super_block *sb, ei = PROC_I(inode); + inode->i_uid = GLOBAL_ROOT_UID; + inode->i_gid = GLOBAL_ROOT_GID; spin_lock(&sysctl_lock); if (unlikely(head->unregistering)) { spin_unlock(&sysctl_lock); iput(inode); return ERR_PTR(-ENOENT); } + /* + * The table, and whatever the owner of the header keeps behind it, + * is only there for as long as nobody unregisters the header, which + * happens under sysctl_lock. So look at them before letting go of it. + */ + mode = table->mode; + if (root->set_ownership) + root->set_ownership(head, &inode->i_uid, &inode->i_gid); ei->sysctl = head; ei->sysctl_entry = table; hlist_add_head_rcu(&ei->sibling_inodes, &head->inodes); @@ -522,8 +533,8 @@ static struct inode *proc_sys_make_inode(struct super_block *sb, spin_unlock(&sysctl_lock); simple_inode_init_ts(inode); - inode->i_mode = table->mode; - if (!S_ISDIR(table->mode)) { + inode->i_mode = mode; + if (!S_ISDIR(mode)) { inode->i_mode |= S_IFREG; inode->i_op = &proc_sys_inode_operations; inode->i_fop = &proc_sys_file_operations; @@ -535,11 +546,6 @@ static struct inode *proc_sys_make_inode(struct super_block *sb, make_empty_dir_inode(inode); } - inode->i_uid = GLOBAL_ROOT_UID; - inode->i_gid = GLOBAL_ROOT_GID; - if (root->set_ownership) - root->set_ownership(head, &inode->i_uid, &inode->i_gid); - return inode; } -- 2.53.0