Christoph Hellwig <hch@xxxxxx> [Tue, 2020-04-21 10:17 -0700]:
> Instead of having all the sysctl handlers deal with user pointers, which
> is rather hairy in terms of the BPF interaction, copy the input to and
> from userspace in common code. This also means that the strings are
> always NUL-terminated by the common code, making the API a little bit
> safer.
>
> As most handler just pass through the data to one of the common handlers
> a lot of the changes are mechnical.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
...
> @@ -1172,36 +1168,28 @@ int __cgroup_bpf_run_filter_sysctl(struct ctl_table_header *head,
> .new_updated = 0,
> };
> struct cgroup *cgrp;
> + loff_t pos = 0;
> int ret;
>
> ctx.cur_val = kmalloc_track_caller(ctx.cur_len, GFP_KERNEL);
> - if (ctx.cur_val) {
> - mm_segment_t old_fs;
> - loff_t pos = 0;
> -
> - old_fs = get_fs();
> - set_fs(KERNEL_DS);
> - if (table->proc_handler(table, 0, (void __user *)ctx.cur_val,
> - &ctx.cur_len, &pos)) {
> - /* Let BPF program decide how to proceed. */
> - ctx.cur_len = 0;
> - }
> - set_fs(old_fs);
> - } else {
> + if (!ctx.cur_val ||
> + table->proc_handler(table, 0, ctx.cur_val, &ctx.cur_len, &pos)) {
> /* Let BPF program decide how to proceed. */
> ctx.cur_len = 0;
> }
>
> - if (write && buf && *pcount) {
> + if (write && *buf && *pcount) {
> /* BPF program should be able to override new value with a
> * buffer bigger than provided by user.
> */
> ctx.new_val = kmalloc_track_caller(PAGE_SIZE, GFP_KERNEL);
> ctx.new_len = min_t(size_t, PAGE_SIZE, *pcount);
> - if (!ctx.new_val ||
> - copy_from_user(ctx.new_val, buf, ctx.new_len))
> + if (ctx.new_val) {
> + memcpy(ctx.new_val, *buf, ctx.new_len);
> + } else {
> /* Let BPF program decide how to proceed. */
> ctx.new_len = 0;
> + }
> }
>
> rcu_read_lock();
> @@ -1212,7 +1200,7 @@ int __cgroup_bpf_run_filter_sysctl(struct ctl_table_header *head,
> kfree(ctx.cur_val);
>
> if (ret == 1 && ctx.new_updated) {
> - *new_buf = ctx.new_val;
> + *buf = ctx.new_val;
Original value of *buf should be freed before overriding it here
otherwise it's lost/leaked unless I missed something.
Other than this BPF part of this patch looks good to me. Feel free to
add my Ack on the next iteration with this fix.
> *pcount = ctx.new_len;
> } else {
> kfree(ctx.new_val);
--
Andrey Ignatov
