[PATCH RFC 1/4] powerpc/crash_dump: check ioremap_cache() in copy_oldmem_page()

[Christian Brauner <brauner@kernel.org>]

copy_oldmem_page() maps a page of the old kernel that isn't in the
linear mapping with ioremap_cache() and copies from it without checking
whether the mapping worked. If it didn't, the copy reads from an offset
into the NULL page. That oopses unless the copy happens to be a user
copy, whose exception table entries turn the fault into a short copy.

Return -ENOMEM like the other architectures do. read_from_oldmem()
turns that into -EFAULT like any other short copy.

Reported-by: Chris Mason <mason@kernel.org>
Fixes: 54c32021eb6f ("[PATCH] powerpc: Add arch-dependent copy_oldmem_page")
Cc: stable@vger.kernel.org
Reviewed-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 arch/powerpc/kernel/crash_dump.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/kernel/crash_dump.c b/arch/powerpc/kernel/crash_dump.c
index 103b6605dd68f..1543917bd3e1d 100644
--- a/arch/powerpc/kernel/crash_dump.c
+++ b/arch/powerpc/kernel/crash_dump.c
@@ -86,6 +86,8 @@ ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn,
 		csize = copy_to_iter(vaddr + offset, csize, iter);
 	} else {
 		vaddr = ioremap_cache(paddr, PAGE_SIZE);
+		if (!vaddr)
+			return -ENOMEM;
 		csize = copy_to_iter(vaddr + offset, csize, iter);
 		iounmap(vaddr);
 	}

-- 
2.53.0