> 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@xxxxxxxxxxxxxxxxxxxxx/ > > Fixes: ff7ec8dc1b64 ("proc: use the same treatment to check proc_lseek as ones for proc_read_iter et.al") > Cc: stable@xxxxxxxxxxxxxxx > Reported-by: Lars Wendler <polynomial-c@xxxxxx> > Signed-off-by: wangzijie <wangzijie1@xxxxxxxxx> > --- > 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(-) > > diff --git a/fs/proc/generic.c b/fs/proc/generic.c > index 76e800e38..bd0c099cf 100644 > --- a/fs/proc/generic.c > +++ b/fs/proc/generic.c > @@ -367,6 +367,25 @@ static const struct inode_operations proc_dir_inode_operations = { > .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) > @@ -374,6 +393,8 @@ 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 +582,6 @@ 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 +592,6 @@ 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 +642,6 @@ 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 +672,6 @@ 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 Hi all, Sorry for disturbing, Brad reported type confusion introduced by this patch to me, we missed a part in the definition of proc_dir_entry: union { const struct proc_ops *proc_ops; const struct file_operations *proc_dir_ops; }; Quoting the email he sent to me: " any dereference of ->proc_ops assuming it is a proc_ops structure results in type confusion, it probably won't be (easily) noticed without CONFIG_RANDSTRUCT because of the way in which proc_flags overlaps with the module owner pointer in the file_operations structure(and the alignment of the struct module pointed to). With RANDSTRUCT enabled, users are likely to observe warnings on proc dir removal like: [ 19.093369] removing permanent /proc entry '12/i8042' [ 19.093396] WARNING: CPU: 0 PID: 1 at fs/proc/generic.c:886 remove_proc_subtree+0xcc/0x218 " I examined where proc_register() is called, we can do !S_ISDIR(dp->mode) test before calling pde_set_flags() to fix it(Brad also suggested to do this), or we can drop this patch and apply the initial version[1]. I think the former is better. Dose anyone have any suggestions? [1] https://lore.kernel.org/all/20250818040535.564611-1-wangzijie1@xxxxxxxxx/.
