coredump: refactor page range dumping into common helper

Both fs/binfmt_elf.c and fs/binfmt_elf_fdpic.c need to dump ranges of
pages into the coredump file.  Extract that logic into a common helper.

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "Eric W . Biederman" <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Link: http://lkml.kernel.org/r/20200827114932.3572699-4-jannh@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 34 insertions, 0 deletions

diff --git a/fs/coredump.c b/fs/coredump.c
index 5e24c06092c98..6042d15acd51f 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -876,6 +876,40 @@ int dump_skip(struct coredump_params *cprm, size_t nr)
 }
 EXPORT_SYMBOL(dump_skip);
 
+#ifdef CONFIG_ELF_CORE
+int dump_user_range(struct coredump_params *cprm, unsigned long start,
+		    unsigned long len)
+{
+	unsigned long addr;
+
+	for (addr = start; addr < start + len; addr += PAGE_SIZE) {
+		struct page *page;
+		int stop;
+
+		/*
+		 * To avoid having to allocate page tables for virtual address
+		 * ranges that have never been used yet, and also to make it
+		 * easy to generate sparse core files, use a helper that returns
+		 * NULL when encountering an empty page table entry that would
+		 * otherwise have been filled with the zero page.
+		 */
+		page = get_dump_page(addr);
+		if (page) {
+			void *kaddr = kmap(page);
+
+			stop = !dump_emit(cprm, kaddr, PAGE_SIZE);
+			kunmap(page);
+			put_page(page);
+		} else {
+			stop = !dump_skip(cprm, PAGE_SIZE);
+		}
+		if (stop)
+			return 0;
+	}
+	return 1;
+}
+#endif
+
 int dump_align(struct coredump_params *cprm, int align)
 {
 	unsigned mod = cprm->pos & (align - 1);