alloc_tag: fix use-after-free in /proc/allocinfo after module unload

allocinfo_start() only reinitializes the codetag iterator at position 0. For subsequent reads (position > 0), it reuses cached iterator state from the previous batch. allocinfo_stop() drops mod_lock between read batches, which allows module unload to complete and free the module memory that the cached iterator still references: CPU0 (read) CPU1 (rmmod) ---- ---- allocinfo_start(pos=0) down_read(mod_lock) allocinfo_show() ... allocinfo_stop() up_read(mod_lock) codetag_unload_module() kfree(cmod) release_module_tags() ... free_mod_mem() allocinfo_start(pos=N) down_read(mod_lock) // reuses cached iter, skips re-init allocinfo_show() ct->filename <-- UAF After free_mod_mem() frees the module's .rodata, allocinfo_show() dereferences ct->filename, ct->function which point there. Save the iterator state in allocinfo_next() and resume from it in allocinfo_start() with codetag_next_ct(), which detects module removal via idr_find() returning NULL and skips to the next module.

Hao Ge committed 5 months ago

Commit 29562681 parent 0c3a3501 file · +7 −2Browse files

Showing the changes to lib (1 of 1 file). Show all

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lib/alloc_tag.c+7−2

@@ -45,6 +45,7 @@ int alloc_tag_ref_offs; · 44 unmodified lines
45	45
46	46	struct allocinfo_private {
47	47	struct codetag_iterator iter;
	48	+ struct codetag_iterator reported_iter;
48	49	bool print_header;
49	50	};
50	51
@@ -58,16 +59,20 @@ static void allocinfo_start(struct seq_file m, loff_t *pos) · 7 unmodified lines
58	59	if (node == 0) {
59	60	priv->print_header = true;
60	61	priv->iter = codetag_get_ct_iter(alloc_tag_cttype);
61		− codetag_next_ct(&priv->iter);
	62	+ } else {
	63	+ priv->iter = priv->reported_iter;
62	64	}
	65	+ codetag_next_ct(&priv->iter);
63	66	return priv->iter.ct ? priv : NULL;
64	67	}
65	68
66	69	static void allocinfo_next(struct seq_file m, void arg, loff_t pos)
67	70	{
68	71	struct allocinfo_private priv = (struct allocinfo_private )arg;
69		− struct codetag *ct = codetag_next_ct(&priv->iter);
	72	+ struct codetag *ct;
70	73
	74	+ priv->reported_iter = priv->iter;
	75	+ ct = codetag_next_ct(&priv->iter);
71	76	(*pos)++;
72	77	if (!ct)
73	78	return NULL;