firmware: arm_scmi: Fix possible scmi_linux_errmap buffer overflow

[ Upstream commit 7a691f16ccad05d770f813d9c4b4337a30c6d63f ]

The scmi_linux_errmap buffer access index is supposed to depend on the
array size to prevent element out of bounds access. It uses SCMI_ERR_MAX
to check bounds but that can mismatch with the array size. It also
changes the success into -EIO though scmi_linux_errmap is never used in
case of success, it is expected to work for success case too.

It is slightly confusing code as the negative of the error code
is used as index to the buffer. Fix it by negating it at the start and
make it more readable.

Link: https://lore.kernel.org/r/20210707135028.1869642-1-sudeep.holla@arm.com
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index 7b6903bad4085408e5e435d37131cf33d002b73d..ba2e18d9e0e4341301c37261275129c4758bce36 100644 (file)
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -54,7 +54,6 @@ enum scmi_error_codes {
        SCMI_ERR_GENERIC = -8,  /* Generic Error */
        SCMI_ERR_HARDWARE = -9, /* Hardware Error */
        SCMI_ERR_PROTOCOL = -10,/* Protocol Error */
-       SCMI_ERR_MAX
 };
 
 /* List of all SCMI devices active in system */
@@ -176,8 +175,10 @@ static const int scmi_linux_errmap[] = {
 
 static inline int scmi_to_linux_errno(int errno)
 {
-       if (errno < SCMI_SUCCESS && errno > SCMI_ERR_MAX)
-               return scmi_linux_errmap[-errno];
+       int err_idx = -errno;
+
+       if (err_idx >= SCMI_SUCCESS && err_idx < ARRAY_SIZE(scmi_linux_errmap))
+               return scmi_linux_errmap[err_idx];
        return -EIO;
 }