net: pktgen: fix hex32_arg parsing for short reads

Fix hex32_arg parsing for short reads (here 7 hex digits instead of the
expected 8), shift result only on successful input parsing.

- before the patch

	$ echo "mpls 0000123" > /proc/net/pktgen/lo\@0
	$ grep mpls /proc/net/pktgen/lo\@0
	     mpls: 00001230
	Result: OK: mpls=00001230

- with patch applied

	$ echo "mpls 0000123" > /proc/net/pktgen/lo\@0
	$ grep mpls /proc/net/pktgen/lo\@0
	     mpls: 00000123
	Result: OK: mpls=00000123

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250219084527.20488-4-ps.report@gmx.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index 4f8ec6c9bed4..28dbbf70e142 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -753,14 +753,15 @@ static int hex32_arg(const char __user *user_buffer, unsigned long maxlen,
 	for (; i < maxlen; i++) {
 		int value;
 		char c;
-		*num <<= 4;
 		if (get_user(c, &user_buffer[i]))
 			return -EFAULT;
 		value = hex_to_bin(c);
-		if (value >= 0)
+		if (value >= 0) {
+			*num <<= 4;
 			*num |= value;
-		else
+		} else {
 			break;
+		}
 	}
 	return i;
 }