pstore/ram: Avoid NULL deref in ftrace merging failure path

Given corruption in the ftrace records, it might be possible to allocate
tmp_prz without assigning prz to it, but still marking it as needing to
be freed, which would cause at least a NULL dereference.

smatch warnings:
fs/pstore/ram.c:340 ramoops_pstore_read() error: we previously assumed 'prz' could be null (see line 255)

https://lists.01.org/pipermail/kbuild-all/2018-December/055528.html

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 2fbea82bbb89 ("pstore: Merge per-CPU ftrace records into one")
Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index e6d9560..96f7d32 100644 (file)
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -291,6 +291,7 @@ static ssize_t ramoops_pstore_read(struct pstore_record *record)
                                          GFP_KERNEL);
                        if (!tmp_prz)
                                return -ENOMEM;
+                       prz = tmp_prz;
                        free_prz = true;
 
                        while (cxt->ftrace_read_cnt < cxt->max_ftrace_cnt) {
@@ -309,7 +310,6 @@ static ssize_t ramoops_pstore_read(struct pstore_record *record)
                                        goto out;
                        }
                        record->id = 0;
-                       prz = tmp_prz;
                }
        }