[PATCH v3 2/4] lib/dump_stack: Add dump_stack_print_cmdline() and wire up in dump_stack_print_info()

[Helge Deller <deller@gmx.de>]

Add the function dump_stack_print_cmdline() which can be used by arch
code to print the command line of the current processs.  This function
is useful in arch code when dumping information for a faulting process.

Wire this function up in the dump_stack_print_info() function to include
the dumping of the command line for architectures which use
dump_stack_print_info().

As an example, with this patch a failing glibc testcase (which uses
ld.so.1 as starting program) up to now reported just "ld.so.1" failing:

 do_page_fault() command='ld.so.1' type=15 address=0x565921d8 in libc.so[f7339000+1bb000]
 trap #15: Data TLB miss fault, vm_start = 0x0001a000, vm_end = 0x0001b000

and now it reports in addition:

 ld.so.1[1151] cmdline: /home/gnu/glibc/objdir/elf/ld.so.1 --library-path /home/gnu/glibc/objdir:/home/gnu/glibc/objdir/math:/home/gnu/
    /home/gnu/glibc/objdir/malloc/tst-safe-linking-malloc-hugetlb1

Josh Triplett noted that dumping such command line parameters into
syslog may theoretically lead to information disclosure.
That's why this patch checks the value of the kptr_restrict sysctl
variable and will not print any information if kptr_restrict==2, and
will not show the program parameters if kptr_restrict==1.

Signed-off-by: Helge Deller <deller@gmx.de>
---
 include/linux/printk.h |  5 +++++
 lib/dump_stack.c       | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/include/linux/printk.h b/include/linux/printk.h
index cf7d666ab1f8..5290a32a197d 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -191,6 +191,7 @@ u32 log_buf_len_get(void);
 void log_buf_vmcoreinfo_setup(void);
 void __init setup_log_buf(int early);
 __printf(1, 2) void dump_stack_set_arch_desc(const char *fmt, ...);
+void dump_stack_print_cmdline(const char *log_lvl);
 void dump_stack_print_info(const char *log_lvl);
 void show_regs_print_info(const char *log_lvl);
 extern asmlinkage void dump_stack_lvl(const char *log_lvl) __cold;
@@ -262,6 +263,10 @@ static inline __printf(1, 2) void dump_stack_set_arch_desc(const char *fmt, ...)
 {
 }

+static inline void dump_stack_print_cmdline(const char *log_lvl)
+{
+}
+
 static inline void dump_stack_print_info(const char *log_lvl)
 {
 }
diff --git a/lib/dump_stack.c b/lib/dump_stack.c
index 83471e81501a..38ef1067c7eb 100644
--- a/lib/dump_stack.c
+++ b/lib/dump_stack.c
@@ -14,6 +14,7 @@
 #include <linux/kexec.h>
 #include <linux/utsname.h>
 #include <linux/stop_machine.h>
+#include <linux/proc_fs.h>

 static char dump_stack_arch_desc_str[128];

@@ -45,6 +46,37 @@ void __init dump_stack_set_arch_desc(const char *fmt, ...)
 #define BUILD_ID_VAL ""
 #endif

+/**
+ * dump_stack_print_cmdline - print the command line of current process
+ * @log_lvl: log level
+ */
+void dump_stack_print_cmdline(const char *log_lvl)
+{
+	char cmdline[256];
+
+	if (kptr_restrict >= 2)
+		return; /* never show command line */
+
+	/* get command line */
+	get_task_cmdline_kernel(current, cmdline, sizeof(cmdline));
+
+	if (kptr_restrict == 1) {
+		char *p;
+
+		/* if restricted show program path only */
+		p = strchr(cmdline, ' ');
+		if (p) {
+			*p = 0;
+			strlcat(cmdline,
+				" ... [parameters hidden due to kptr_restrict]",
+				sizeof(cmdline));
+		}
+	}
+
+	printk("%s%s[%d] cmdline: %s\n", log_lvl, current->comm,
+		current->pid, cmdline);
+}
+
 /**
  * dump_stack_print_info - print generic debug info for dump_stack()
  * @log_lvl: log level
@@ -62,6 +94,8 @@ void dump_stack_print_info(const char *log_lvl)
 	       (int)strcspn(init_utsname()->version, " "),
 	       init_utsname()->version, BUILD_ID_VAL);

+	dump_stack_print_cmdline(log_lvl);
+
 	if (dump_stack_arch_desc_str[0] != '\0')
 		printk("%sHardware name: %s\n",
 		       log_lvl, dump_stack_arch_desc_str);
--
2.37.1