[tip: objtool/urgent] objtool, Input: cyapa - Remove undefined behavior in cyapa_update_fw_store()

[tip-bot2 for Josh Poimboeuf]

The following commit has been merged into the objtool/urgent branch of tip:

Commit-ID:     7501153750b47416c9891038330359fad0205839
Gitweb:        https://git.kernel.org/tip/7501153750b47416c9891038330359fad0205839
Author:        Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate:    Mon, 24 Mar 2025 14:56:08 -07:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 25 Mar 2025 23:00:15 +01:00

objtool, Input: cyapa - Remove undefined behavior in cyapa_update_fw_store()

In cyapa_update_fw_store(), if 'count' is zero, the write to
fw_name[count-1] underflows the array.

Presumably that's not possible in normal operation, as its caller
sysfs_kf_write() already checks for zero.  Regardless it's a good idea
to check for the error explicitly and avoid undefined behavior.

Fixes the following warning with an UBSAN kernel:

  vmlinux.o: warning: objtool: .text.cyapa_update_fw_store: unexpected end of section

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/73ae0bb3c656735890d914b74c9d6bb40c25d3cd.1742852847.git.jpoimboe@xxxxxxxxxx
Closes: https://lore.kernel.org/oe-kbuild-all/202503171547.LlCTJLQL-lkp@xxxxxxxxx/
---
 drivers/input/mouse/cyapa.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/input/mouse/cyapa.c b/drivers/input/mouse/cyapa.c
index 2f2d925..00c87c0 100644
--- a/drivers/input/mouse/cyapa.c
+++ b/drivers/input/mouse/cyapa.c
@@ -1080,8 +1080,8 @@ static ssize_t cyapa_update_fw_store(struct device *dev,
 	char fw_name[NAME_MAX];
 	int ret, error;
 
-	if (count >= NAME_MAX) {
-		dev_err(dev, "File name too long\n");
+	if (!count || count >= NAME_MAX) {
+		dev_err(dev, "Bad file name size\n");
 		return -EINVAL;
 	}