From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792838330; b=Nt2T5I03/jQ2ca+6ss16/bii4SPpaeNApzjE9LYcV7G5BsYIrdbjVVf4hT7gXtGU6T/1 lMFGnyhKnHE0d8NpgD/7o/mwvEhQPaIDV/4Olcj++YJx67PvGv9svcE43YDzzZ51wNWy8 oxbMo+beTe4DA8qURiZYiccCkV56b44CCDS3zARyEnLGLeMQ/DTaKHA+3bK/xYpOan4ui SZqTiJf/iA06LvYvvDKW4/FNGzDOYsaWee1KoLXNYQXn7tow8bsCS9psgZ6Mc+tRqsw+e cQ1B4dlmU5iepthhkfLsuBvemHveDW71h9JfZNggxRuP8Jm/PriCAJuzX8fRU6X6X4w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792838330; h=Received:DKIM-Signature:From:Date:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:Message-Id:References:In-Reply-To:To:Cc: X-Mailer:X-Developer-Signature:X-Developer-Key; bh=nebGk1L2zCEOU9a6O+PMjW2jKWlO0OdmHkddKi+rvCI=; b=2HwrwxYgdARZr1d03s+M7A9wcZ9OnmCsUg9eJ9liv/Wq+R3sqKdAu15WdLLEdpRfWp/e pUAgCxFgJdh+3G7nPVUn8/rHCq6h94vwhE9p9VL3SLwNt5TVtY2tdGaZxtSWCGOP7wQ9C I9GA1tk9/Gpr5vc4k6kJOLZ4+y3nutjLlG0ME5v1yuxygJYvJ+mRk3iW1GU8c3s7KkE/b w5jpHZVv0WedJPB/QNhBco4IMggec3DyXG+xvq97HzYYeup2JZ1WgK3s+BljqhemsmD/l 67SGTbi9Ze3ASxprHK5jQYMzXwcehMC44ls/h8HtczWpkSn5y+U7tAvdwxIl9eE4qGw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=C8MYPe02; 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 7784B606A323; Sat, 24 Oct 2026 10:38:50 +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=C8MYPe02 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6C6411F01829; Sat, 24 Oct 2026 10:38:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792838330; bh=nebGk1L2zCEOU9a6O+PMjW2jKWlO0OdmHkddKi+rvCI=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=C8MYPe02LZo/z9zKlIYGPFuUEXVX9j39GHtuAUNc4dJd20gtXk7FzQtKVP70QC+j1 2Jq3WDn0cHTOleNodmVBBb1AxcGPDO9W61B1rGmY+2/xf00oDsIBG8DX3TwHicduDL xVym67C7CK1qZi0OvE7RbfHOaxMKH306GGmo094pX13afS7MMsEjoZKlgROBAFp+vH 2LkXl8ceozQuWPhgMx8ysEbgmxiogzvGXesaNbFQwTqRZC81GozoshsikoOCl1PTN+ cvfnEKOUY0ZAfTGyHUG0XYTiBXeQYsfQ8b4XoelPd98UBZc6gaYOGDyDtBnxyxIZK2 q/5iLbBeCSy+A== From: Christian Brauner Date: Sat, 24 Oct 2026 12:38:29 +0200 Subject: [PATCH 3/7] proc: don't let /proc/mounts and /proc/net be mountpoints X-Mailing-List: linux-fsdevel@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" Content-Transfer-Encoding: 7bit Message-Id: <20261024-work-procfs-fixes-v1-3-46b03c3a8fac@kernel.org> References: <20261024-work-procfs-fixes-v1-0-46b03c3a8fac@kernel.org> In-Reply-To: <20261024-work-procfs-fixes-v1-0-46b03c3a8fac@kernel.org> To: linux-fsdevel@vger.kernel.org Cc: linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org, Alexander Viro , Jan Kara , Aleksa Sarai , Chris Mason , "Christian Brauner (Amutable)" X-Mailer: b4 0.17-dev-ce4c1 X-Developer-Signature: v=1; a=openpgp-sha256; l=5327; i=brauner@kernel.org; h=from:subject:message-id; bh=5yGvCWpvDnxnRfGkGjsuQ1EryC7aWF4E0Ou1WptRHYQ=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWTd6Vrnm5fCGfIl+/Up67d/lrY8O28z3XGlhJ6PiaeTT k/T6ZklHaUsDGJcDLJiiiwO7Sbhcst5KjYbZWrAzGFlAhnCwMUpABM5Y8bIcP+a6cS0A2mbAmcV vQlnMNHOnlp4wf92h/dCw4QM9jkx8xj+Ozosbt7he3BjYu+J2zFKdccvBqp3vmb7Pf1Wl920d2k BvAA= X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 /proc/mounts and /proc/net are links into /proc/self. Like /proc/self itself they resolve differently for every process. A mount on one of the links redirects the lookup for all processes in that mount namespace. Add proc_self_symlink() for links that point into /proc/self. It creates the link with PROC_ENTRY_CANT_MOUNT and proc_lookup_de() splices such an entry with proc_splice_unmountable(). Use it for /proc/mounts and /proc/net. Mounting through the links keeps working. Such a mount lands on the caller's own /proc//mounts or /proc//net, not on the link. Signed-off-by: Christian Brauner (Amutable) --- fs/proc/generic.c | 26 ++++++++++++++++++++++++-- fs/proc/proc_net.c | 2 +- fs/proc/root.c | 2 +- include/linux/proc_fs.h | 5 +++++ 4 files changed, 31 insertions(+), 4 deletions(-) diff --git a/fs/proc/generic.c b/fs/proc/generic.c index 4c3fcaf68ef4..484d7dc123eb 100644 --- a/fs/proc/generic.c +++ b/fs/proc/generic.c @@ -260,6 +260,10 @@ struct dentry *proc_lookup_de(struct inode *dir, struct dentry *dentry, if (de->flags & PROC_ENTRY_FORCE_LOOKUP) return proc_splice_unmountable(inode, dentry, &proc_net_dentry_ops); + /* a mount on a link into /proc/self redirects every process */ + if (de->flags & PROC_ENTRY_CANT_MOUNT) + return proc_splice_unmountable(inode, dentry, + &proc_misc_dentry_ops); return d_splice_alias_ops(inode, dentry, &proc_misc_dentry_ops); } @@ -487,8 +491,8 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent, return ent; } -struct proc_dir_entry *proc_symlink(const char *name, - struct proc_dir_entry *parent, const char *dest) +static struct proc_dir_entry *__proc_symlink(const char *name, + struct proc_dir_entry *parent, const char *dest, u8 flags) { struct proc_dir_entry *ent; @@ -496,6 +500,7 @@ struct proc_dir_entry *proc_symlink(const char *name, (S_IFLNK | S_IRUGO | S_IWUGO | S_IXUGO),1); if (ent) { + ent->flags |= flags; ent->size = strlen(dest); ent->data = kmemdup(dest, ent->size + 1, GFP_KERNEL); if (ent->data) { @@ -508,8 +513,25 @@ struct proc_dir_entry *proc_symlink(const char *name, } return ent; } + +struct proc_dir_entry *proc_symlink(const char *name, + struct proc_dir_entry *parent, const char *dest) +{ + return __proc_symlink(name, parent, dest, 0); +} EXPORT_SYMBOL(proc_symlink); +/* + * A link into /proc/self resolves differently for every process, so a + * mount on the link itself would redirect all of them. + */ +struct proc_dir_entry *proc_self_symlink(const char *name, + struct proc_dir_entry *parent, const char *dest) +{ + return __proc_symlink(name, parent, dest, PROC_ENTRY_CANT_MOUNT); +} +EXPORT_SYMBOL_GPL(proc_self_symlink); + struct proc_dir_entry *_proc_mkdir(const char *name, umode_t mode, struct proc_dir_entry *parent, void *data, bool force_lookup) { diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c index b1f5eafb069a..578b1eb081bf 100644 --- a/fs/proc/proc_net.c +++ b/fs/proc/proc_net.c @@ -420,7 +420,7 @@ static struct pernet_operations __net_initdata proc_net_ns_ops = { int __init proc_net_init(void) { - proc_symlink("net", NULL, "self/net"); + proc_self_symlink("net", NULL, "self/net"); return register_pernet_subsys(&proc_net_ns_ops); } diff --git a/fs/proc/root.c b/fs/proc/root.c index 7fbbe92bf73a..42fdc6ec50a3 100644 --- a/fs/proc/root.c +++ b/fs/proc/root.c @@ -380,7 +380,7 @@ void __init proc_root_init(void) set_proc_pid_nlink(); proc_self_init(); proc_thread_self_init(); - proc_symlink("mounts", NULL, "self/mounts"); + proc_self_symlink("mounts", NULL, "self/mounts"); proc_net_init(); proc_mkdir("fs", NULL); diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h index 47d7deaeed8f..903fc811efd4 100644 --- a/include/linux/proc_fs.h +++ b/include/linux/proc_fs.h @@ -29,6 +29,7 @@ enum { PROC_ENTRY_proc_compat_ioctl = 1U << 2, PROC_ENTRY_proc_lseek = 1U << 3, + PROC_ENTRY_CANT_MOUNT = 1U << 6, PROC_ENTRY_FORCE_LOOKUP = 1U << 7, }; @@ -87,6 +88,8 @@ extern void proc_flush_pid(struct pid *); extern struct proc_dir_entry *proc_symlink(const char *, struct proc_dir_entry *, const char *); +struct proc_dir_entry *proc_self_symlink(const char *, struct proc_dir_entry *, + const char *); struct proc_dir_entry *_proc_mkdir(const char *, umode_t, struct proc_dir_entry *, void *, bool); extern struct proc_dir_entry *proc_mkdir(const char *, struct proc_dir_entry *); extern struct proc_dir_entry *proc_mkdir_data(const char *, umode_t, @@ -179,6 +182,8 @@ static inline void proc_flush_pid(struct pid *pid) static inline struct proc_dir_entry *proc_symlink(const char *name, struct proc_dir_entry *parent,const char *dest) { return NULL;} +static inline struct proc_dir_entry *proc_self_symlink(const char *name, + struct proc_dir_entry *parent, const char *dest) { return NULL; } static inline struct proc_dir_entry *proc_mkdir(const char *name, struct proc_dir_entry *parent) {return NULL;} static inline struct proc_dir_entry *proc_create_mount_point(const char *name) { return NULL; } -- 2.53.0