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.henriq...@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;
 }
--
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