The existing handler function take the struct ctl_table as a mutable parameter. This prevents the table definitions from being put into .rodata where they would be protected from accidental or malicious modification. As many parts of the kernel define proc_handlers provide a gradual transition mechanism through the introduction of a new field which takes the table as a read-only parameter. Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx> --- fs/proc/proc_sysctl.c | 6 ++++-- include/linux/sysctl.h | 17 +++++++++++++---- 2 files changed, 17 insertions(+), 6 deletions(-) diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c index 1bb0aa2ff501..810ecdd3b84c 100644 --- a/fs/proc/proc_sysctl.c +++ b/fs/proc/proc_sysctl.c @@ -573,7 +573,7 @@ static ssize_t proc_sys_call_handler(struct kiocb *iocb, struct iov_iter *iter, /* if that can happen at all, it should be -EINVAL, not -EISDIR */ error = -EINVAL; - if (!table->proc_handler) + if (!table->proc_handler && !table->proc_handler_new) goto out; /* don't even try if the size is too large */ @@ -655,7 +655,7 @@ static __poll_t proc_sys_poll(struct file *filp, poll_table *wait) if (IS_ERR(head)) return EPOLLERR | EPOLLHUP; - if (!table->proc_handler) + if (!table->proc_handler && !table->proc_handler_new) goto out; if (!table->poll) @@ -1333,6 +1333,8 @@ static struct ctl_dir *sysctl_mkdir_p(struct ctl_dir *dir, const char *path) * * proc_handler - the text handler routine (described below) * + * proc_handler_new - const variant of the text handler routine (described below) + * * extra1, extra2 - extra pointers usable by the proc handler routines * XXX: we should eventually modify these to use long min / max [0] * [0] https://lkml.kernel.org/87zgpte9o4.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h index 604aaaa1fce2..de1a5a714070 100644 --- a/include/linux/sysctl.h +++ b/include/linux/sysctl.h @@ -63,6 +63,8 @@ extern const unsigned long sysctl_long_vals[]; typedef int proc_handler(struct ctl_table *ctl, int write, void *buffer, size_t *lenp, loff_t *ppos); +typedef int proc_handler_new(const struct ctl_table *ctl, int write, + void *buffer, size_t *lenp, loff_t *ppos); int proc_dostring(struct ctl_table *, int, void *, size_t *, loff_t *); int proc_dobool(struct ctl_table *table, int write, void *buffer, @@ -107,10 +109,10 @@ int proc_do_static_key(struct ctl_table *table, int write, void *buffer, * struct enable minimal validation of the values being written to be * performed, and the mode field allows minimal authentication. * - * There must be a proc_handler routine for any terminal nodes - * mirrored under /proc/sys (non-terminals are handled by a built-in - * directory handler). Several default handlers are available to - * cover common cases. + * There must be one proc_handler/proc_handler_new routine for any terminal + * nodes mirrored under /proc/sys (non-terminals are handled by a built-in + * directory handler). + * Several default handlers are available to cover common cases. */ /* Support for userspace poll() to watch for changes */ @@ -149,6 +151,7 @@ struct ctl_table { SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY } type; proc_handler *proc_handler; /* Callback for text formatting */ + proc_handler_new *proc_handler_new; /* Callback for text formatting */ struct ctl_table_poll *poll; void *extra1; void *extra2; @@ -301,6 +304,12 @@ int sysctl_max_threads(struct ctl_table *table, int write, void *buffer, static inline int sysctl_run_handler(struct ctl_table *ctl, int write, void *buffer, size_t *lenp, loff_t *ppos) { + if (ctl->proc_handler_new && ctl->proc_handler) + pr_warn_ratelimited("sysctl table %s has both proc_handler and proc_handler_new, this is a but\n", + ctl->procname); + + if (ctl->proc_handler_new) + return ctl->proc_handler_new(ctl, write, buffer, lenp, ppos); return ctl->proc_handler(ctl, write, buffer, lenp, ppos); } -- 2.43.0
