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b=oOTHfPnjZImvmmRPM2MTN/E/IIH+K1Xm8QDVrH8Oqlt/AJsi4waiHv9CftkJy/6ni 6EIRp0HbnhNfXHCXc4K9VojrITUlGyR3GhezVAOLc4o/UIMtBv2UXRIoUyNcRoDRfl hwij2c23hqVe3wrkk0JhAPavUcN3D/QHGIgP+swQEOLquf8jyQsTyTqg2D9L7WX2yM 2YVUuBtbVOY3/D4t49N5Yy+FRqPEDXIaeGHoQTT7h7Tt3ELLZfedzkDX06MymVZHGo gZ83lZ/ZcoL9USNS1bfrcS7dOsq69wrvT9Qy2snDigPKgQfSdgsNGiZ+ZmulPoiK7N lLvjE7UUh2gCA== From: Christian Brauner Date: Mon, 02 Nov 2026 15:21:36 +0100 Subject: [PATCH RFC 21/38] proc: let proc_remove() remove the entry it was given X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261102-work-procfs-bugfixes-v1-21-59422ed3e465@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 X-Mailer: b4 0.17-dev X-Developer-Signature: v=1; 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If the entry was removed already, say along with its parent, that is either nothing or a different entry that got the same name in the meantime, and de->parent may well be gone. Two removals of the same entry are a bug in the caller, but going by the name turns it into removing an entry that belongs to somebody else. Since commit 895b4c0c79b0 ("fs/proc: fix uaf in proc_readdir_de()") an entry that was unlinked has an empty rb node. So check for that under proc_subdir_lock and otherwise remove the entry itself, with the loop of remove_proc_subtree() moved into a helper both of them use. Nothing can help a caller that passes an entry that has been freed already. Reported-by: Chris Mason Fixes: a8ca16ea7b0a ("proc: Supply a function to remove a proc entry by PDE") Signed-off-by: Christian Brauner (Amutable) --- fs/proc/generic.c | 78 ++++++++++++++++++++++++++++++++++++------------------- 1 file changed, 51 insertions(+), 27 deletions(-) diff --git a/fs/proc/generic.c b/fs/proc/generic.c index 47830d6af255..23fc026d7bbb 100644 --- a/fs/proc/generic.c +++ b/fs/proc/generic.c @@ -817,33 +817,14 @@ void remove_proc_entry(const char *name, struct proc_dir_entry *parent) } EXPORT_SYMBOL(remove_proc_entry); -int remove_proc_subtree(const char *name, struct proc_dir_entry *parent) +/* + * Remove @root, already erased from its parent, and everything below it. + * Called with proc_subdir_lock held for writing, returns with it dropped. + */ +static int __remove_proc_subtree(struct proc_dir_entry *root) { - struct proc_dir_entry *root = NULL, *de, *next; - const char *fn = name; - unsigned int len; - - write_lock(&proc_subdir_lock); - if (__xlate_proc_name(name, &parent, &fn) != 0) { - write_unlock(&proc_subdir_lock); - return -ENOENT; - } - len = strlen(fn); + struct proc_dir_entry *de = root, *next; - root = pde_subdir_find(parent, fn, len); - if (!root) { - write_unlock(&proc_subdir_lock); - return -ENOENT; - } - if (unlikely(pde_is_permanent(root))) { - write_unlock(&proc_subdir_lock); - WARN(1, "removing permanent /proc entry '%s/%s'", - root->parent->name, root->name); - return -EINVAL; - } - pde_erase(root, parent); - - de = root; while (1) { next = pde_subdir_first(de); if (next) { @@ -871,6 +852,34 @@ int remove_proc_subtree(const char *name, struct proc_dir_entry *parent) pde_put(root); return 0; } + +int remove_proc_subtree(const char *name, struct proc_dir_entry *parent) +{ + struct proc_dir_entry *root = NULL; + const char *fn = name; + unsigned int len; + + write_lock(&proc_subdir_lock); + if (__xlate_proc_name(name, &parent, &fn) != 0) { + write_unlock(&proc_subdir_lock); + return -ENOENT; + } + len = strlen(fn); + + root = pde_subdir_find(parent, fn, len); + if (!root) { + write_unlock(&proc_subdir_lock); + return -ENOENT; + } + if (unlikely(pde_is_permanent(root))) { + write_unlock(&proc_subdir_lock); + WARN(1, "removing permanent /proc entry '%s/%s'", + root->parent->name, root->name); + return -EINVAL; + } + pde_erase(root, parent); + return __remove_proc_subtree(root); +} EXPORT_SYMBOL(remove_proc_subtree); void *proc_get_parent_data(const struct inode *inode) @@ -882,8 +891,23 @@ EXPORT_SYMBOL_GPL(proc_get_parent_data); void proc_remove(struct proc_dir_entry *de) { - if (de) - remove_proc_subtree(de->name, de->parent); + if (!de) + return; + + write_lock(&proc_subdir_lock); + /* Removed already, maybe along with its parent. */ + if (RB_EMPTY_NODE(&de->subdir_node)) { + write_unlock(&proc_subdir_lock); + return; + } + if (unlikely(pde_is_permanent(de))) { + write_unlock(&proc_subdir_lock); + WARN(1, "removing permanent /proc entry '%s/%s'", + de->parent->name, de->name); + return; + } + pde_erase(de, de->parent); + __remove_proc_subtree(de); } EXPORT_SYMBOL(proc_remove); -- 2.53.0