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Mon, 2 Nov 2026 14:46:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793630812; bh=gGh9qQAToZE5wrWgcgjg72Buy8fnK2LgswQGjbfg87A=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=k68ttWG6wR2uYUNWQI+ECVf+fO/XJ0eqvyJRIGqlTdn3SeSK5FwYTdTBaVjsoBsYJ kJXwecLDVVqkc0QtPna5nnmOaGhEH6lV2p3+n4SMeLLTjqLfMHRMfS6+IdU5FeP6Ex EEbVMiiZNLXMTNclGmw6p8mC8yLNPYuUSTnCtn6ZR27qjgY9RaX2RJuHLWLPx9jmMt 9JJmAL/6SUvZypF7nop8NC5qp7LgJYP8eJFNNtNBvtdk7y2N5+2qF+LGhO9FlXYxla LSU+v/oAHtst3btNP9gxZgyUrKBFNLcCwNm+jD4+mesxl+NmeCWqzBEWi80sNRNQ/1 Y+2ZOSQK06ITw== From: Christian Brauner Date: Mon, 02 Nov 2026 15:43:28 +0100 Subject: [PATCH RFC 37/38] proc: don't pin a symlink's entry while readlink() copies it out X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , Precedence: list X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261102-work-procfs-bugfixes-v1-37-59422ed3e465@kernel.org> References: <20261102-work-procfs-bugfixes-v1-0-59422ed3e465@kernel.org> In-Reply-To: <20261102-work-procfs-bugfixes-v1-0-59422ed3e465@kernel.org> 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 , stable@vger.kernel.org X-Mailer: b4 0.17-dev X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 proc_get_link() pins the entry with use_pde() and the delayed call unpins it. vfs_readlink() copies the link to userspace in between. So a page fault in that copy holds up remove_proc_entry() just like the copies of reads and writes do, and the callers hold locks while they wait. /proc/asound/ is removed with snd_card_mutex and info_mutex held when a card changes its id. The pin doesn't keep anything alive. proc_symlink() copies the target and pde_free() frees it with the entry, and the inode holds a reference to the entry. What the pin does is keep a removed symlink from being followed. So check ->in_use instead and drop the delayed call. That also takes an atomic pair off every traversal of /proc/net and /proc/mounts. Fixes: 7e0e953bb0cf ("procfs: fix race between symlink removals and traversals") Cc: stable@vger.kernel.org Signed-off-by: Christian Brauner (Amutable) --- fs/proc/inode.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/fs/proc/inode.c b/fs/proc/inode.c index 9933f03ab9fb..2d65f3c8ec03 100644 --- a/fs/proc/inode.c +++ b/fs/proc/inode.c @@ -629,19 +629,19 @@ static const struct file_operations proc_iter_file_ops_compat = { }; #endif -static void proc_put_link(void *p) -{ - unuse_pde(p); -} - static const char *proc_get_link(struct dentry *dentry, struct inode *inode, struct delayed_call *done) { struct proc_dir_entry *pde = PDE(inode); - if (!use_pde(pde)) + + /* + * No pin. The link lives with the entry, which the inode holds, and a + * reader could fault while vfs_readlink() copies it out. Just don't + * follow a removed one. + */ + if (unlikely(atomic_read(&pde->in_use) < 0)) return ERR_PTR(-EINVAL); - set_delayed_call(done, proc_put_link, pde); return pde->data; } -- 2.53.0