coredump: rework elf/elf_fdpic vma_dump_size() into common helper

At the moment, the binfmt_elf and binfmt_elf_fdpic code have slightly
different code to figure out which VMAs should be dumped, and if so,
whether the dump should contain the entire VMA or just its first page.

Eliminate duplicate code by reworking the binfmt_elf version into a
generic core dumping helper in coredump.c.

As part of that, change the heuristic for detecting executable/library
header pages to check whether the inode is executable instead of looking
at the file mode.

This is less problematic in terms of locking because it lets us avoid
get_user() under the mmap_sem.  (And arguably it looks nicer and makes
more sense in generic code.)

Adjust a little bit based on the binfmt_elf_fdpic version: ->anon_vma is
only meaningful under CONFIG_MMU, otherwise we have to assume that the VMA
has been written to.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
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/20200827114932.3572699-5-jannh@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 79 deletions

diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index 76e8c0defdc8..f531c6198864 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -1215,76 +1215,6 @@ struct elf_prstatus_fdpic
 	int pr_fpvalid;		/* True if math co-processor being used.  */
 };
 
-/*
- * Decide whether a segment is worth dumping; default is yes to be
- * sure (missing info is worse than too much; etc).
- * Personally I'd include everything, and use the coredump limit...
- *
- * I think we should skip something. But I am not sure how. H.J.
- */
-static int maydump(struct vm_area_struct *vma, unsigned long mm_flags)
-{
-	int dump_ok;
-
-	/* Do not dump I/O mapped devices or special mappings */
-	if (vma->vm_flags & VM_IO) {
-		kdcore("%08lx: %08lx: no (IO)", vma->vm_start, vma->vm_flags);
-		return 0;
-	}
-
-	/* If we may not read the contents, don't allow us to dump
-	 * them either. "dump_write()" can't handle it anyway.
-	 */
-	if (!(vma->vm_flags & VM_READ)) {
-		kdcore("%08lx: %08lx: no (!read)", vma->vm_start, vma->vm_flags);
-		return 0;
-	}
-
-	/* support for DAX */
-	if (vma_is_dax(vma)) {
-		if (vma->vm_flags & VM_SHARED) {
-			dump_ok = test_bit(MMF_DUMP_DAX_SHARED, &mm_flags);
-			kdcore("%08lx: %08lx: %s (DAX shared)", vma->vm_start,
-			       vma->vm_flags, dump_ok ? "yes" : "no");
-		} else {
-			dump_ok = test_bit(MMF_DUMP_DAX_PRIVATE, &mm_flags);
-			kdcore("%08lx: %08lx: %s (DAX private)", vma->vm_start,
-			       vma->vm_flags, dump_ok ? "yes" : "no");
-		}
-		return dump_ok;
-	}
-
-	/* By default, dump shared memory if mapped from an anonymous file. */
-	if (vma->vm_flags & VM_SHARED) {
-		if (file_inode(vma->vm_file)->i_nlink == 0) {
-			dump_ok = test_bit(MMF_DUMP_ANON_SHARED, &mm_flags);
-			kdcore("%08lx: %08lx: %s (share)", vma->vm_start,
-			       vma->vm_flags, dump_ok ? "yes" : "no");
-			return dump_ok;
-		}
-
-		dump_ok = test_bit(MMF_DUMP_MAPPED_SHARED, &mm_flags);
-		kdcore("%08lx: %08lx: %s (share)", vma->vm_start,
-		       vma->vm_flags, dump_ok ? "yes" : "no");
-		return dump_ok;
-	}
-
-#ifdef CONFIG_MMU
-	/* By default, if it hasn't been written to, don't write it out */
-	if (!vma->anon_vma) {
-		dump_ok = test_bit(MMF_DUMP_MAPPED_PRIVATE, &mm_flags);
-		kdcore("%08lx: %08lx: %s (!anon)", vma->vm_start,
-		       vma->vm_flags, dump_ok ? "yes" : "no");
-		return dump_ok;
-	}
-#endif
-
-	dump_ok = test_bit(MMF_DUMP_ANON_PRIVATE, &mm_flags);
-	kdcore("%08lx: %08lx: %s", vma->vm_start, vma->vm_flags,
-	       dump_ok ? "yes" : "no");
-	return dump_ok;
-}
-
 /* An ELF note in memory */
 struct memelfnote
 {
@@ -1529,13 +1459,9 @@ static bool elf_fdpic_dump_segments(struct coredump_params *cprm)
 	struct vm_area_struct *vma;
 
 	for (vma = current->mm->mmap; vma; vma = vma->vm_next) {
-		unsigned long addr;
-
-		if (!maydump(vma, cprm->mm_flags))
-			continue;
+		unsigned long size = vma_dump_size(vma, cprm->mm_flags);
 
-		if (!dump_user_range(cprm, vma->vm_start,
-				     vma->vma_end - vma->vm_start))
+		if (!dump_user_range(cprm, vma->vm_start, size))
 			return false;
 	}
 	return true;
@@ -1547,8 +1473,7 @@ static size_t elf_core_vma_data_size(unsigned long mm_flags)
 	size_t size = 0;
 
 	for (vma = current->mm->mmap; vma; vma = vma->vm_next)
-		if (maydump(vma, mm_flags))
-			size += vma->vm_end - vma->vm_start;
+		size += vma_dump_size(vma, mm_flags);
 	return size;
 }
 
@@ -1694,7 +1619,7 @@ static int elf_fdpic_core_dump(struct coredump_params *cprm)
 		phdr.p_offset = offset;
 		phdr.p_vaddr = vma->vm_start;
 		phdr.p_paddr = 0;
-		phdr.p_filesz = maydump(vma, cprm->mm_flags) ? sz : 0;
+		phdr.p_filesz = vma_dump_size(vma, cprm->mm_flags);
 		phdr.p_memsz = sz;
 		offset += phdr.p_filesz;
 		phdr.p_flags = vma->vm_flags & VM_READ ? PF_R : 0;