Archive/lede/target/linux/generic/backport-6.6/621-proc-fix-missing-pde_set_flags.patch

From: wangzijie <wangzijie1@honor.com>
To: <akpm@linux-foundation.org>, <brauner@kernel.org>,
	<viro@zeniv.linux.org.uk>, <adobriyan@gmail.com>,
	<rick.p.edgecombe@intel.com>, <ast@kernel.org>,
	<k.shutemov@gmail.com>, <jirislaby@kernel.org>,
	<linux-fsdevel@vger.kernel.org>
Cc: <polynomial-c@gmx.de>, <gregkh@linuxfoundation.org>,
	<stable@vger.kernel.org>, <regressions@lists.linux.dev>,
	wangzijie <wangzijie1@honor.com>
Subject: [PATCH v3] proc: fix missing pde_set_flags() for net proc files
Date: Thu, 21 Aug 2025 18:58:06 +0800	[thread overview]
Message-ID: <20250821105806.1453833-1-wangzijie1@honor.com> (raw)

To avoid potential UAF issues during module removal races, we use pde_set_flags()
to save proc_ops flags in PDE itself before proc_register(), and then use
pde_has_proc_*() helpers instead of directly dereferencing pde->proc_ops->*.

However, the pde_set_flags() call was missing when creating net related proc files.
This omission caused incorrect behavior which FMODE_LSEEK was being cleared
inappropriately in proc_reg_open() for net proc files. Lars reported it in this link[1].

Fix this by ensuring pde_set_flags() is called when register proc entry, and add
NULL check for proc_ops in pde_set_flags().

[1]: https://lore.kernel.org/all/20250815195616.64497967@chagall.paradoxon.rec/

Fixes: ff7ec8dc1b64 ("proc: use the same treatment to check proc_lseek as ones for proc_read_iter et.al")
Cc: stable@vger.kernel.org
Reported-by: Lars Wendler <polynomial-c@gmx.de>
Signed-off-by: wangzijie <wangzijie1@honor.com>
---
v3:
- followed by Christian's suggestion to stash pde->proc_ops in a local const variable
v2:
- followed by Jiri's suggestion to refractor code and reformat commit message
---
 fs/proc/generic.c | 38 +++++++++++++++++++++-----------------
 1 file changed, 21 insertions(+), 17 deletions(-)

--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -362,6 +362,25 @@ static const struct inode_operations pro
 	.setattr	= proc_notify_change,
 };
 
+static void pde_set_flags(struct proc_dir_entry *pde)
+{
+	const struct proc_ops *proc_ops = pde->proc_ops;
+
+	if (!proc_ops)
+		return;
+
+	if (proc_ops->proc_flags & PROC_ENTRY_PERMANENT)
+		pde->flags |= PROC_ENTRY_PERMANENT;
+	if (proc_ops->proc_read_iter)
+		pde->flags |= PROC_ENTRY_proc_read_iter;
+#ifdef CONFIG_COMPAT
+	if (proc_ops->proc_compat_ioctl)
+		pde->flags |= PROC_ENTRY_proc_compat_ioctl;
+#endif
+	if (proc_ops->proc_lseek)
+		pde->flags |= PROC_ENTRY_proc_lseek;
+}
+
 /* returns the registered entry, or frees dp and returns NULL on failure */
 struct proc_dir_entry *proc_register(struct proc_dir_entry *dir,
 		struct proc_dir_entry *dp)
@@ -369,6 +388,8 @@ struct proc_dir_entry *proc_register(str
 	if (proc_alloc_inum(&dp->low_ino))
 		goto out_free_entry;
 
+	pde_set_flags(dp);
+
 	write_lock(&proc_subdir_lock);
 	dp->parent = dir;
 	if (pde_subdir_insert(dir, dp) == false) {
@@ -557,20 +578,6 @@ struct proc_dir_entry *proc_create_reg(c
 	return p;
 }
 
-static void pde_set_flags(struct proc_dir_entry *pde)
-{
-	if (pde->proc_ops->proc_flags & PROC_ENTRY_PERMANENT)
-		pde->flags |= PROC_ENTRY_PERMANENT;
-	if (pde->proc_ops->proc_read_iter)
-		pde->flags |= PROC_ENTRY_proc_read_iter;
-#ifdef CONFIG_COMPAT
-	if (pde->proc_ops->proc_compat_ioctl)
-		pde->flags |= PROC_ENTRY_proc_compat_ioctl;
-#endif
-	if (pde->proc_ops->proc_lseek)
-		pde->flags |= PROC_ENTRY_proc_lseek;
-}
-
 struct proc_dir_entry *proc_create_data(const char *name, umode_t mode,
 		struct proc_dir_entry *parent,
 		const struct proc_ops *proc_ops, void *data)
@@ -581,7 +588,6 @@ struct proc_dir_entry *proc_create_data(
 	if (!p)
 		return NULL;
 	p->proc_ops = proc_ops;
-	pde_set_flags(p);
 	return proc_register(parent, p);
 }
 EXPORT_SYMBOL(proc_create_data);
@@ -632,7 +638,6 @@ struct proc_dir_entry *proc_create_seq_p
 	p->proc_ops = &proc_seq_ops;
 	p->seq_ops = ops;
 	p->state_size = state_size;
-	pde_set_flags(p);
 	return proc_register(parent, p);
 }
 EXPORT_SYMBOL(proc_create_seq_private);
@@ -663,7 +668,6 @@ struct proc_dir_entry *proc_create_singl
 		return NULL;
 	p->proc_ops = &proc_single_ops;
 	p->single_show = show;
-	pde_set_flags(p);
 	return proc_register(parent, p);
 }
 EXPORT_SYMBOL(proc_create_single_data);