[PATCH 5.12 238/292] rtc: fix snprintf() checking in is_rtc_hctosys()

From: Greg Kroah-Hartman
Date: Mon Jul 19 2021 - 14:12:27 EST

From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

[ Upstream commit 54b909436ede47e0ee07f1765da27ec2efa41e84 ]

The scnprintf() function silently truncates the printf() and returns
the number bytes that it was able to copy (not counting the NUL
terminator). Thus, the highest value it can return here is
"NAME_SIZE - 1" and the overflow check is dead code. Fix this by
using the snprintf() function which returns the number of bytes that
would have been copied if there was enough space and changing the
condition from "> NAME_SIZE" to ">= NAME_SIZE".

Fixes: 92589c986b33 ("rtc-proc: permit the /proc/driver/rtc device to use other devices")
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/YJov/pcGmhLi2pEl@mwanda
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
drivers/rtc/proc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/rtc/proc.c b/drivers/rtc/proc.c
index 73344598fc1b..cbcdbb19d848 100644
--- a/drivers/rtc/proc.c
+++ b/drivers/rtc/proc.c
@@ -23,8 +23,8 @@ static bool is_rtc_hctosys(struct rtc_device *rtc)
int size;
char name[NAME_SIZE];

- size = scnprintf(name, NAME_SIZE, "rtc%d", rtc->id);
- if (size > NAME_SIZE)
+ size = snprintf(name, NAME_SIZE, "rtc%d", rtc->id);
+ if (size >= NAME_SIZE)
return false;

return !strncmp(name, CONFIG_RTC_HCTOSYS_DEVICE, NAME_SIZE);