[PATCH] pstore: ram_core: fix incorrect success return when vmap() fails

[ruipengqi <ruipengqi3@gmail.com>]

From: Ruipeng Qi <ruipengqi3@gmail.com>

In persistent_ram_vmap(), vmap() may return NULL on failure.

If offset is non-zero, adding offset_in_page(start) causes the function
to return a non-NULL pointer even though the mapping failed.
persistent_ram_buffer_map() therefore incorrectly returns success.

Subsequent access to prz->buffer may dereference an invalid address
and cause crashes.

Add proper NULL checking for vmap() failures.

Signed-off-by: Ruipeng Qi <ruipengqi3@gmail.com>
---
 fs/pstore/ram_core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
index f1848cdd6d34..f8b9b47e8b24 100644
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -446,6 +446,13 @@ static void *persistent_ram_vmap(phys_addr_t start, size_t size,
 	vaddr = vmap(pages, page_count, VM_MAP | VM_IOREMAP, prot);
 	kfree(pages);
 
+	/*
+	 * vmap() may fail and return NULL. Do not add the offset in this
+	 * case, otherwise a NULL mapping would appear successful.
+	 */
+	if (!vaddr)
+		return NULL;
+
 	/*
 	 * Since vmap() uses page granularity, we must add the offset
 	 * into the page here, to get the byte granularity address
-- 
2.25.1