linux-kernel - [PATCH 4.19 57/81] mm/vmpressure.c: fix a signedness bug in vmpressure_register

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Message-Id: <20191016214842.957825220@linuxfoundation.org>
Date:   Wed, 16 Oct 2019 14:51:08 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dan Carpenter <dan.carpenter@...cle.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Enrico Weigelt <info@...ux.net>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.19 57/81] mm/vmpressure.c: fix a signedness bug in vmpressure_register_event()

From: Dan Carpenter <dan.carpenter@...cle.com>

commit 518a86713078168acd67cf50bc0b45d54b4cce6c upstream.

The "mode" and "level" variables are enums and in this context GCC will
treat them as unsigned ints so the error handling is never triggered.

I also removed the bogus initializer because it isn't required any more
and it's sort of confusing.

[akpm@...ux-foundation.org: reduce implicit and explicit typecasting]
[akpm@...ux-foundation.org: fix return value, add comment, per Matthew]
Link: http://lkml.kernel.org/r/20190925110449.GO3264@mwanda
Fixes: 3cadfa2b9497 ("mm/vmpressure.c: convert to use match_string() helper")
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Acked-by: David Rientjes <rientjes@...gle.com>
Reviewed-by: Matthew Wilcox <willy@...radead.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Enrico Weigelt <info@...ux.net>
Cc: Kate Stewart <kstewart@...uxfoundation.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/vmpressure.c |   20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -358,6 +358,9 @@ void vmpressure_prio(gfp_t gfp, struct m
  * "hierarchy" or "local").
  *
  * To be used as memcg event method.
+ *
+ * Return: 0 on success, -ENOMEM on memory failure or -EINVAL if @args could
+ * not be parsed.
  */
 int vmpressure_register_event(struct mem_cgroup *memcg,
 			      struct eventfd_ctx *eventfd, const char *args)
@@ -365,7 +368,7 @@ int vmpressure_register_event(struct mem
 	struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
 	struct vmpressure_event *ev;
 	enum vmpressure_modes mode = VMPRESSURE_NO_PASSTHROUGH;
-	enum vmpressure_levels level = -1;
+	enum vmpressure_levels level;
 	char *spec, *spec_orig;
 	char *token;
 	int ret = 0;
@@ -378,20 +381,18 @@ int vmpressure_register_event(struct mem
 
 	/* Find required level */
 	token = strsep(&spec, ",");
-	level = match_string(vmpressure_str_levels, VMPRESSURE_NUM_LEVELS, token);
-	if (level < 0) {
-		ret = level;
+	ret = match_string(vmpressure_str_levels, VMPRESSURE_NUM_LEVELS, token);
+	if (ret < 0)
 		goto out;
-	}
+	level = ret;
 
 	/* Find optional mode */
 	token = strsep(&spec, ",");
 	if (token) {
-		mode = match_string(vmpressure_str_modes, VMPRESSURE_NUM_MODES, token);
-		if (mode < 0) {
-			ret = mode;
+		ret = match_string(vmpressure_str_modes, VMPRESSURE_NUM_MODES, token);
+		if (ret < 0)
 			goto out;
-		}
+		mode = ret;
 	}
 
 	ev = kzalloc(sizeof(*ev), GFP_KERNEL);
@@ -407,6 +408,7 @@ int vmpressure_register_event(struct mem
 	mutex_lock(&vmpr->events_lock);
 	list_add(&ev->node, &vmpr->events);
 	mutex_unlock(&vmpr->events_lock);
+	ret = 0;
 out:
 	kfree(spec_orig);
 	return ret;