Fix root mounting with no mount options

The "trivial conversion" in commit cccaa5e33525 ("init: use do_mount()
instead of ksys_mount()") was totally broken, since it didn't handle the
case of a NULL mount data pointer.  And while I had "tested" it (and
presumably Dominik had too) that bug was hidden by me having options.

Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Reported-by: Ondřej Jirman <megi@xff.cz>
Reported-by: Guenter Roeck <linux@roeck-us.net>
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reported-and-tested-by: Borislav Petkov <bp@suse.de>
Tested-by: Chris Clayton <chris2553@googlemail.com>
Tested-by: Eric Biggers <ebiggers@kernel.org>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Tested-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/init/do_mounts.c b/init/do_mounts.c
index f55cbd9cb8183f9a36b4da4e2f59c5a1720621c3..0ae9cc22f2ae255c55337812b121a9a2d2eec9ca 100644 (file)
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -391,17 +391,19 @@ static int __init do_mount_root(const char *name, const char *fs,
                                 const int flags, const void *data)
 {
        struct super_block *s;
-       char *data_page;
-       struct page *p;
+       struct page *p = NULL;
+       char *data_page = NULL;
        int ret;
 
-       /* do_mount() requires a full page as fifth argument */
-       p = alloc_page(GFP_KERNEL);
-       if (!p)
-               return -ENOMEM;
-
-       data_page = page_address(p);
-       strncpy(data_page, data, PAGE_SIZE - 1);
+       if (data) {
+               /* do_mount() requires a full page as fifth argument */
+               p = alloc_page(GFP_KERNEL);
+               if (!p)
+                       return -ENOMEM;
+               data_page = page_address(p);
+               /* zero-pad. do_mount() will make sure it's terminated */
+               strncpy(data_page, data, PAGE_SIZE);
+       }
 
        ret = do_mount(name, "/root", fs, flags, data_page);
        if (ret)
@@ -417,7 +419,8 @@ static int __init do_mount_root(const char *name, const char *fs,
               MAJOR(ROOT_DEV), MINOR(ROOT_DEV));
 
 out:
-       put_page(p);
+       if (p)
+               put_page(p);
        return ret;
 }