pstore: Fix NULL pointer fault if get NULL prz in ramoops_get_next_prz

ramoops_get_next_prz get the prz according the paramters. If it get a
uninitialized prz, access its members by following persistent_ram_old_size(prz)
will cause a NULL pointer crash.
Ex: if ftrace_size is 0, fprz will be NULL.

Fix it by return NULL in advance.

Signed-off-by: Liu ShuoX <shuox.liu@intel.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index 1daed280f1b6..6f96d8c2a711 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -119,6 +119,8 @@ ramoops_get_next_prz(struct persistent_ram_zone *przs[], uint *c, uint max,
                 return NULL;
 
         prz = przs[i];
+        if (!prz)
+                return NULL;
 
         /* Update old/shadowed buffer. */
         if (update)