kconfig: undefined symbols can crash dependency loop detection

The Kconfig

config FOO
bool "FOO" if BAR
select BAR

has a dependency loop involving an undefined symbol BAR. This causes a segfault in sym_check_print_recursive() as it assumes all symbols have a non-null 'prop', which is not the case for undefined symbols. This is a proposed fix.

Signed-off-by Ulf Magnusson <[email protected]>

---
 scripts/kconfig/symbol.c |   32 ++++++++++++++++++++++++++++----
 1 files changed, 28 insertions(+), 4 deletions(-)

scripts/kconfig/symbol.c +12 -0

index a796c95..81a217f 100644
@@ -5,6 +5,7 @@
 
 #include <ctype.h>
 #include <stdlib.h>
+#include <stdio.h>
 #include <string.h>
 #include <regex.h>
 #include <sys/utsname.h>

@@ -972,6 +973,10 @@ static void sym_check_print_recursive(struct symbol *last_sym)
 	struct menu *menu = NULL;
 	struct property *prop;
 	struct dep_stack cv_stack;
+	const char *filename;
+	int lineno;
+	char undef_msg_buf[100];
+	int snprintf_size;
 
 	if (sym_is_choice_value(last_sym)) {
 		dep_stack_insert(&cv_stack, last_sym);

@@ -1001,18 +1006,37 @@ static void sym_check_print_recursive(struct symbol *last_sym)
 					break;
 			}
 		}
+
+		if (prop) {
+			filename = prop->file->name;
+			lineno = prop->lineno;
+		} else {
+			/* The dependency loop involves an undefined symbol.
+			 * Checking sym->name is probably unnecessary here, but

Quoted 58 lines · Ulf Magnusson

The Kconfig

config FOO
bool "FOO" if BAR
select BAR

has a dependency loop involving an undefined symbol BAR. This causes a segfault in sym_check_print_recursive() as it assumes all symbols have a non-null 'prop', which is not the case for undefined symbols. This is a proposed fix.

Signed-off-by Ulf Magnusson <[email protected]>

---
 scripts/kconfig/symbol.c |   32 ++++++++++++++++++++++++++++----
 1 files changed, 28 insertions(+), 4 deletions(-)

scripts/kconfig/symbol.c +20 -0

index a796c95..81a217f 100644
@@ -5,6 +5,7 @@
 
 #include <ctype.h>
 #include <stdlib.h>
+#include <stdio.h>
 #include <string.h>
 #include <regex.h>
 #include <sys/utsname.h>

@@ -972,6 +973,10 @@ static void sym_check_print_recursive(struct symbol *last_sym)
 	struct menu *menu = NULL;
 	struct property *prop;
 	struct dep_stack cv_stack;
+	const char *filename;
+	int lineno;
+	char undef_msg_buf[100];
+	int snprintf_size;
 
 	if (sym_is_choice_value(last_sym)) {
 		dep_stack_insert(&cv_stack, last_sym);

@@ -1001,18 +1006,37 @@ static void sym_check_print_recursive(struct symbol *last_sym)
 					break;
 			}
 		}
+
+		if (prop) {
+			filename = prop->file->name;
+			lineno = prop->lineno;
+		} else {
+			/* The dependency loop involves an undefined symbol.
+			 * Checking sym->name is probably unnecessary here, but
+			 * just to be on the safe side. */
+			snprintf_size = snprintf(undef_msg_buf,
+						 sizeof(undef_msg_buf),
+						 "<no file, %s is undefined>",
+						 sym->name ? sym->name :
+							     "<choice>");
+			if (snprintf_size > sizeof(undef_msg_buf))
+				undef_msg_buf[sizeof(undef_msg_buf) - 1] = '\0';

scripts/kconfig/symbol.c static void sym_check_print_recursive(struct symbol *last_sym) · line 1025

Quoted 2 lines

scripts/kconfig/symbol.c +2 -0

+			filename = undef_msg_buf;
+			lineno = 0;

Good catch. But as this handles a corner case involving a severely borken Kconfig file, I would simply do
filename = "<unknown>";
lineno = 0;
and be done with it.