pstore/ramoops: fixup driver removal

A basic rmmod ramoops segfaults. Let's see why.

Since commit 34f0ec82e0a9 ("pstore: Correct the max_dump_cnt clearing of
ramoops") sets ->max_dump_cnt to zero before looping over ->przs but we
didn't use it before that either.

And since commit ee1d267423a1 ("pstore: add pstore unregister") we free
that memory on rmmod.

But even then, we looped until a NULL pointer or ERR. I don't see where
it is ensured that the last member is NULL. Let's try this instead:
simply error recovery and free. Clean up in error case where resources
were allocated. And then, in the free path, rely on ->max_dump_cnt in
the free path.

Cc: Anton Vorontsov <anton@enomsg.org>
Cc: Colin Cross <ccross@android.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org # 4.4.x-

1 files changed, 12 insertions, 5 deletions

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index 7a034d62cf8c..2340262a7e97 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -377,13 +377,14 @@ static void ramoops_free_przs(struct ramoops_context *cxt)
 {
         int i;
 
-        cxt->max_dump_cnt = 0;
         if (!cxt->przs)
                 return;
 
-        for (i = 0; !IS_ERR_OR_NULL(cxt->przs[i]); i++)
+        for (i = 0; i < cxt->max_dump_cnt; i++)
                 persistent_ram_free(cxt->przs[i]);
+
         kfree(cxt->przs);
+        cxt->max_dump_cnt = 0;
 }
 
 static int ramoops_init_przs(struct device *dev, struct ramoops_context *cxt,
@@ -408,7 +409,7 @@ static int ramoops_init_przs(struct device *dev, struct ramoops_context *cxt,
                              GFP_KERNEL);
         if (!cxt->przs) {
                 dev_err(dev, "failed to initialize a prz array for dumps\n");
-                goto fail_prz;
+                goto fail_mem;
         }
 
         for (i = 0; i < cxt->max_dump_cnt; i++) {
@@ -419,6 +420,11 @@ static int ramoops_init_przs(struct device *dev, struct ramoops_context *cxt,
                         err = PTR_ERR(cxt->przs[i]);
                         dev_err(dev, "failed to request mem region (0x%zx@0x%llx): %d\n",
                                 cxt->record_size, (unsigned long long)*paddr, err);
+
+                        while (i > 0) {
+                                i--;
+                                persistent_ram_free(cxt->przs[i]);
+                        }
                         goto fail_prz;
                 }
                 *paddr += cxt->record_size;
@@ -426,7 +432,9 @@ static int ramoops_init_przs(struct device *dev, struct ramoops_context *cxt,
 
         return 0;
 fail_prz:
-        ramoops_free_przs(cxt);
+        kfree(cxt->przs);
+fail_mem:
+        cxt->max_dump_cnt = 0;
         return err;
 }
 
@@ -659,7 +667,6 @@ static int ramoops_remove(struct platform_device *pdev)
         struct ramoops_context *cxt = &oops_cxt;
 
         pstore_unregister(&cxt->pstore);
-        cxt->max_dump_cnt = 0;
 
         kfree(cxt->pstore.buf);
         cxt->pstore.bufsize = 0;