[PATCH v2] proc: fix missing pde_set_flags() for net proc files

[PATCH v2] proc: fix missing pde_set_flags() for net proc files

[wangzijie]

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)
Reported-by: Lars Wendler <polynomial-c@gmx.de>
Signed-off-by: wangzijie <wangzijie1@honor.com>
---
v2:
- followed by Jiri's suggestion to refractor code and reformat commit message
---
 fs/proc/generic.c | 36 +++++++++++++++++++-----------------
 1 file changed, 19 insertions(+), 17 deletions(-)

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 76e800e38..003031839 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -367,6 +367,23 @@ static const struct inode_operations proc_dir_inode_operations = {
 	.setattr	= proc_notify_change,
 };
 
+static void pde_set_flags(struct proc_dir_entry *pde)
+{
+	if (!pde->proc_ops)
+		return;
+
+	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;
+}
+
 /* 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)
@@ -374,6 +391,8 @@ struct proc_dir_entry *proc_register(struct proc_dir_entry *dir,
 	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) {
@@ -561,20 +580,6 @@ struct proc_dir_entry *proc_create_reg(const char *name, umode_t mode,
 	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)
@@ -585,7 +590,6 @@ struct proc_dir_entry *proc_create_data(const char *name, umode_t mode,
 	if (!p)
 		return NULL;
 	p->proc_ops = proc_ops;
-	pde_set_flags(p);
 	return proc_register(parent, p);
 }
 EXPORT_SYMBOL(proc_create_data);
@@ -636,7 +640,6 @@ struct proc_dir_entry *proc_create_seq_private(const char *name, umode_t mode,
 	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);
@@ -667,7 +670,6 @@ struct proc_dir_entry *proc_create_single_data(const char *name, umode_t mode,
 		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);
-- 
2.25.1

Re: [PATCH v2] proc: fix missing pde_set_flags() for net proc files

[Greg KH]

On Mon, Aug 18, 2025 at 07:24:28PM +0800, wangzijie wrote:
> 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)
> Reported-by: Lars Wendler <polynomial-c@gmx.de>
> Signed-off-by: wangzijie <wangzijie1@honor.com>
> ---
> v2:
> - followed by Jiri's suggestion to refractor code and reformat commit message
> ---
>  fs/proc/generic.c | 36 +++++++++++++++++++-----------------
>  1 file changed, 19 insertions(+), 17 deletions(-)
> 


<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>