[PATCH v2 6/6] zram: unify and harden algo/priority params handling

[Sergey Senozhatsky <senozhatsky@chromium.org>]

We have two functions that accept algo= and priority=
params - algorithm_params_store() and recompress_store().
This patch unifies and hardens handling of those
parameters.

There are 4 possible cases:

- only priority= provided [recommended]
  We need to verify that provided priority value is
  within permitted range for each particular function.

- both algo= and priority= provided
  We cannot prioritize one over another.  All we should
  do is to verify that zram is configured in the way
  that user-space expects it to be.  Namely that zram
  indeed has compressor algo= setup at given priority=.

- only algo= provided [not recommended]
  We should lookup priority in compressors list.

- none provided [not recommended]
  Just use function's defaults.

Suggested-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/zram_drv.c | 106 +++++++++++++++++++++-------------
 1 file changed, 66 insertions(+), 40 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 02fb70f35ae8..676b1602d817 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1635,6 +1635,37 @@ static void zram_debugfs_register(struct zram *zram) {};
 static void zram_debugfs_unregister(struct zram *zram) {};
 #endif
 
+/* Only algo parameter given, lookup by algo name */
+static int lookup_algo_priority(struct zram *zram, const char *algo,
+				u32 min_prio)
+{
+	s32 prio;
+
+	for (prio = min_prio; prio < ZRAM_MAX_COMPS; prio++) {
+		if (!zram->comp_algs[prio])
+			continue;
+
+		if (!strcmp(zram->comp_algs[prio], algo))
+			return prio;
+	}
+
+	return -EINVAL;
+}
+
+/* Both algo and priority parameters given, validate them */
+static int validate_algo_priority(struct zram *zram, const char *algo, u32 prio)
+{
+	if (prio >= ZRAM_MAX_COMPS)
+		return -EINVAL;
+	/* No algo at given priority */
+	if (!zram->comp_algs[prio])
+		return -EINVAL;
+	/* A different algo at given priority */
+	if (strcmp(zram->comp_algs[prio], algo))
+		return -EINVAL;
+	return 0;
+}
+
 static void comp_algorithm_set(struct zram *zram, u32 prio, const char *alg)
 {
 	zram->comp_algs[prio] = alg;
@@ -1707,6 +1738,7 @@ static ssize_t algorithm_params_store(struct device *dev,
 	char *args, *param, *val, *algo = NULL, *dict_path = NULL;
 	struct deflate_params deflate_params;
 	struct zram *zram = dev_to_zram(dev);
+	bool prio_param = false;
 	int ret;
 
 	deflate_params.winbits = ZCOMP_PARAM_NOT_SET;
@@ -1719,6 +1751,7 @@ static ssize_t algorithm_params_store(struct device *dev,
 			return -EINVAL;
 
 		if (!strcmp(param, "priority")) {
+			prio_param = true;
 			ret = kstrtoint(val, 10, &prio);
 			if (ret)
 				return ret;
@@ -1754,24 +1787,22 @@ static ssize_t algorithm_params_store(struct device *dev,
 	if (init_done(zram))
 		return -EBUSY;
 
-	/* Lookup priority by algorithm name */
-	if (algo) {
-		s32 p;
-
-		prio = -EINVAL;
-		for (p = ZRAM_PRIMARY_COMP; p < ZRAM_MAX_COMPS; p++) {
-			if (!zram->comp_algs[p])
-				continue;
+	if (prio_param) {
+		if (prio < ZRAM_PRIMARY_COMP || prio >= ZRAM_MAX_COMPS)
+			return -EINVAL;
+	}
 
-			if (!strcmp(zram->comp_algs[p], algo)) {
-				prio = p;
-				break;
-			}
-		}
+	if (algo && prio_param) {
+		ret = validate_algo_priority(zram, algo, prio);
+		if (ret)
+			return ret;
 	}
 
-	if (prio < ZRAM_PRIMARY_COMP || prio >= ZRAM_MAX_COMPS)
-		return -EINVAL;
+	if (algo && !prio_param) {
+		prio = lookup_algo_priority(zram, algo, ZRAM_PRIMARY_COMP);
+		if (prio < 0)
+			return -EINVAL;
+	}
 
 	ret = comp_params_store(zram, prio, level, dict_path, &deflate_params);
 	return ret ? ret : len;
@@ -2407,9 +2438,6 @@ static int recompress_slot(struct zram *zram, u32 index, struct page *page,
 	void *src;
 	int ret = 0;
 
-	if (!zram->comps[prio])
-		return -EINVAL;
-
 	handle_old = get_slot_handle(zram, index);
 	if (!handle_old)
 		return -EINVAL;
@@ -2511,10 +2539,11 @@ static ssize_t recompress_store(struct device *dev,
 	char *args, *param, *val, *algo = NULL;
 	u64 num_recomp_pages = ULLONG_MAX;
 	struct zram_pp_ctl *ctl = NULL;
-	u32 prio = ZRAM_SECONDARY_COMP;
-	struct zram_pp_slot *pps;
+	s32 prio = ZRAM_SECONDARY_COMP;
 	u32 mode = 0, threshold = 0;
+	struct zram_pp_slot *pps;
 	struct page *page = NULL;
+	bool prio_param = false;
 	ssize_t ret;
 
 	args = skip_spaces(buf);
@@ -2562,7 +2591,8 @@ static ssize_t recompress_store(struct device *dev,
 		}
 
 		if (!strcmp(param, "priority")) {
-			ret = kstrtouint(val, 10, &prio);
+			prio_param = true;
+			ret = kstrtoint(val, 10, &prio);
 			if (ret)
 				return ret;
 			continue;
@@ -2576,30 +2606,26 @@ static ssize_t recompress_store(struct device *dev,
 	if (!init_done(zram))
 		return -EINVAL;
 
-	if (algo) {
-		bool found = false;
-
-		for (; prio < ZRAM_MAX_COMPS; prio++) {
-			if (!zram->comp_algs[prio])
-				continue;
-
-			if (!strcmp(zram->comp_algs[prio], algo)) {
-				found = true;
-				break;
-			}
-		}
+	if (prio_param) {
+		if (prio < ZRAM_SECONDARY_COMP || prio >= ZRAM_MAX_COMPS)
+			return -EINVAL;
+	}
 
-		if (!found) {
-			ret = -EINVAL;
-			goto out;
-		}
+	if (algo && prio_param) {
+		ret = validate_algo_priority(zram, algo, prio);
+		if (ret)
+			return ret;
 	}
 
-	if (prio < ZRAM_SECONDARY_COMP || prio >= ZRAM_MAX_COMPS) {
-		ret = -EINVAL;
-		goto out;
+	if (algo && !prio_param) {
+		prio = lookup_algo_priority(zram, algo, ZRAM_SECONDARY_COMP);
+		if (prio < 0)
+			return -EINVAL;
 	}
 
+	if (!zram->comps[prio])
+		return -EINVAL;
+
 	page = alloc_page(GFP_KERNEL);
 	if (!page) {
 		ret = -ENOMEM;
-- 
2.53.0.473.g4a7958ca14-goog