zram: off by one in read_block_state()

[ Upstream commit a88e03cf3d190cf46bc4063a9b7efe87590de5f4 ]

snprintf() returns the number of bytes it would have printed if there
were space.  But it does not count the NUL terminator.  So that means
that if "count == copied" then this has already overflowed by one
character.

This bug likely isn't super harmful in real life.

Link: https://lkml.kernel.org/r/20210916130404.GA25094@kili
Fixes: c0265342bff4 ("zram: introduce zram memory tracking")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index fcaf275..6383c81 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -910,7 +910,7 @@ static ssize_t read_block_state(struct file *file, char __user *buf,
                        zram_test_flag(zram, index, ZRAM_HUGE) ? 'h' : '.',
                        zram_test_flag(zram, index, ZRAM_IDLE) ? 'i' : '.');
 
-               if (count < copied) {
+               if (count <= copied) {
                        zram_slot_unlock(zram, index);
                        break;
                }