[PATCH 2/3] s390/boot: Avoid IPL parameter append past command line

[Vasily Gorbik <gor@linux.ibm.com>]

A command line may occupy all but the terminating byte of
COMMAND_LINE_SIZE. In that case append_ipl_block_parm() passes a zero size
to the IPL parameter conversion helpers and points the destination one
byte past early_command_line. The helpers subtract one from the unsigned
size and write the converted parameter outside the command line buffer.

Convert the IPL parameter in the command line parsing buffer first. A
parameter beginning with '=' can then replace the existing command line
regardless of its length, while other parameters are appended only when
space remains.

Fixes: 5ecb2da660ab ("s390: support command lines longer than 896 bytes")
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
---
 arch/s390/boot/ipl_parm.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/arch/s390/boot/ipl_parm.c b/arch/s390/boot/ipl_parm.c
index 6bc950b92be7..8aa7639ae0cb 100644
--- a/arch/s390/boot/ipl_parm.c
+++ b/arch/s390/boot/ipl_parm.c
@@ -23,6 +23,7 @@ struct parmarea parmarea __section(".parmarea") = {
 };
 
 char __bootdata(early_command_line)[COMMAND_LINE_SIZE];
+static char command_line_buf[COMMAND_LINE_SIZE];
 
 unsigned int __bootdata_preserved(zlib_dfltcc_support) = ZLIB_DFLTCC_FULL;
 struct ipl_parameter_block __bootdata_preserved(ipl_block);
@@ -135,31 +136,32 @@ static size_t ipl_block_get_ascii_scpdata(char *dest, size_t size,
 
 static void append_ipl_block_parm(void)
 {
-	char *parm, *delim;
+	char *delim;
 	size_t len, rc = 0;
 
 	len = strlen(early_command_line);
-
-	delim = early_command_line + len;    /* '\0' character position */
-	parm = early_command_line + len + 1; /* append right after '\0' */
+	delim = early_command_line + len; /* '\0' character position */
 
 	switch (ipl_block.pb0_hdr.pbt) {
 	case IPL_PBT_CCW:
 		rc = ipl_block_get_ascii_vmparm(
-			parm, COMMAND_LINE_SIZE - len - 1, &ipl_block);
+			command_line_buf, sizeof(command_line_buf), &ipl_block);
 		break;
 	case IPL_PBT_FCP:
 	case IPL_PBT_NVME:
 	case IPL_PBT_ECKD:
 		rc = ipl_block_get_ascii_scpdata(
-			parm, COMMAND_LINE_SIZE - len - 1, &ipl_block);
+			command_line_buf, sizeof(command_line_buf), &ipl_block);
 		break;
 	}
 	if (rc) {
-		if (*parm == '=')
-			memmove(early_command_line, parm + 1, rc);
-		else
+		if (command_line_buf[0] == '=') {
+			memmove(early_command_line, command_line_buf + 1, rc);
+		} else if (len < COMMAND_LINE_SIZE - 2) {
 			*delim = ' '; /* replace '\0' with space */
+			sized_strscpy(delim + 1, command_line_buf,
+				       COMMAND_LINE_SIZE - len - 1);
+		}
 	}
 }
 
@@ -245,7 +247,6 @@ static void modify_fac_list(char *str)
 	check_cleared_facilities();
 }
 
-static char command_line_buf[COMMAND_LINE_SIZE];
 void parse_boot_command_line(void)
 {
 	char *param, *val;
-- 
2.53.0