[PATCH v2] fault-injection: Enhance failcmd to exit on non-hex address input

[Breno Leitao]

The failcmd.sh script in the fault-injection toolkit does not currently
validate whether the provided address is in hexadecimal format. This can
lead to silent failures if the address is sourced from places like
`/proc/kallsyms`, which omits the '0x' prefix, potentially causing users
to operate under incorrect assumptions.

Introduce a new function, `exit_if_not_hex`, which checks the format of
the provided address and exits with an error message if the address is
not a valid hexadecimal number.

This enhancement prevents users from running the command with
improperly formatted addresses, thus improving the robustness and
usability of the failcmd tool.

Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
---
Changelog:
 v2:
	* Write error message to stderr (Akinobu Mita)
	* Remove the file permission change (100755) in this patch. Going
 	  to send in a separate patch.

 tools/testing/fault-injection/failcmd.sh | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/tools/testing/fault-injection/failcmd.sh b/tools/testing/fault-injection/failcmd.sh
index 78dac34264be..c4f2432750f4 100644
--- a/tools/testing/fault-injection/failcmd.sh
+++ b/tools/testing/fault-injection/failcmd.sh
@@ -64,6 +64,14 @@ ENVIRONMENT
 EOF
 }
 
+exit_if_not_hex() {
+    local value="$1"
+    if ! [[ $value =~ ^0x[0-9a-fA-F]+$ ]]; then
+        echo "Error: The provided value '$value' is not a valid hexadecimal number." >&2
+        exit 1
+    fi
+}
+
 if [ $UID != 0 ]; then
 	echo must be run as root >&2
 	exit 1
@@ -160,18 +168,22 @@ while true; do
 		shift 2
 		;;
 	--require-start)
+		exit_if_not_hex "$2"
 		echo $2 > $FAULTATTR/require-start
 		shift 2
 		;;
 	--require-end)
+		exit_if_not_hex "$2"
 		echo $2 > $FAULTATTR/require-end
 		shift 2
 		;;
 	--reject-start)
+		exit_if_not_hex "$2"
 		echo $2 > $FAULTATTR/reject-start
 		shift 2
 		;;
 	--reject-end)
+		exit_if_not_hex "$2"
 		echo $2 > $FAULTATTR/reject-end
 		shift 2
 		;;
-- 
2.43.0