[PATCH] zram: don't copy invalid compression algorithms

[Luis Henriques <luis.henriques@canonical.com>]

Validate the new compression algorithm before copying it into the zram
'compressor' field, keeping the old one if it's invalid.

The error path code is also slightly refactored.

Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 drivers/block/zram/zram_drv.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 9c01f5bfa33f..33551ec9e7f5 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -367,10 +367,15 @@ static ssize_t comp_algorithm_store(struct device *dev,
 
 	down_write(&zram->init_lock);
 	if (init_done(zram)) {
-		up_write(&zram->init_lock);
 		pr_info("Can't change algorithm for initialized device\n");
-		return -EBUSY;
+		len = -EBUSY;
+		goto out;
+	}
+	if (!zcomp_available_algorithm(buf)) {
+		len = -EINVAL;
+		goto out;
 	}
+
 	strlcpy(zram->compressor, buf, sizeof(zram->compressor));
 
 	/* ignore trailing newline */
@@ -378,9 +383,7 @@ static ssize_t comp_algorithm_store(struct device *dev,
 	if (sz > 0 && zram->compressor[sz - 1] == '\n')
 		zram->compressor[sz - 1] = 0x00;
 
-	if (!zcomp_available_algorithm(zram->compressor))
-		len = -EINVAL;
-
+out:
 	up_write(&zram->init_lock);
 	return len;
 }