string_helpers: add kstrdup_quotable_cmdline

Provide an escaped (but readable: no inter-argument NULLs) commandline
safe for logging.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.l.morris@oracle.com>

2 files changed, 35 insertions, 0 deletions

diff --git a/include/linux/string_helpers.h b/include/linux/string_helpers.h
index 9de228af00c1..684d2695fc36 100644
--- a/include/linux/string_helpers.h
+++ b/include/linux/string_helpers.h
@@ -69,5 +69,6 @@ static inline int string_escape_str_any_np(const char *src, char *dst,
 }
 
 char *kstrdup_quotable(const char *src, gfp_t gfp);
+char *kstrdup_quotable_cmdline(struct task_struct *task, gfp_t gfp);
 
 #endif
diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index aa00c9f989ee..b16ee85aaf87 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -10,6 +10,7 @@
 #include <linux/export.h>
 #include <linux/ctype.h>
 #include <linux/errno.h>
+#include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/string_helpers.h>
@@ -562,3 +563,36 @@ char *kstrdup_quotable(const char *src, gfp_t gfp)
         return dst;
 }
 EXPORT_SYMBOL_GPL(kstrdup_quotable);
+
+/*
+ * Returns allocated NULL-terminated string containing process
+ * command line, with inter-argument NULLs replaced with spaces,
+ * and other special characters escaped.
+ */
+char *kstrdup_quotable_cmdline(struct task_struct *task, gfp_t gfp)
+{
+        char *buffer, *quoted;
+        int i, res;
+
+        buffer = kmalloc(PAGE_SIZE, GFP_TEMPORARY);
+        if (!buffer)
+                return NULL;
+
+        res = get_cmdline(task, buffer, PAGE_SIZE - 1);
+        buffer[res] = '\0';
+
+        /* Collapse trailing NULLs, leave res pointing to last non-NULL. */
+        while (--res >= 0 && buffer[res] == '\0')
+                ;
+
+        /* Replace inter-argument NULLs. */
+        for (i = 0; i <= res; i++)
+                if (buffer[i] == '\0')
+                        buffer[i] = ' ';
+
+        /* Make sure result is printable. */
+        quoted = kstrdup_quotable(buffer, gfp);
+        kfree(buffer);
+        return quoted;
+}
+EXPORT_SYMBOL_GPL(kstrdup_quotable_cmdline);