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Subject[PATCH -mm 3/3 v2] ELF, coredump: allow process with empty address space to coredump
Unmapping whole address space at once with

munmap(0, (1ULL<<47) - 4096)

or equivalent will create empty coredump.

It is silly way to exit, however registers content may still be useful.

The right to coredump is fundamental right of a process!

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

fs/binfmt_elf.c | 10 +++++-
tools/testing/selftests/exec/Makefile | 1
tools/testing/selftests/exec/coredump-zero-vma.c | 38 +++++++++++++++++++++++
3 files changed, 48 insertions(+), 1 deletion(-)

--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1595,6 +1595,10 @@ static int fill_files_note(struct memelfnote *note)
if (size >= MAX_FILE_NOTE_SIZE) /* paranoia check */
return -EINVAL;
size = round_up(size, PAGE_SIZE);
+ /*
+ * "size" can be 0 here legitimately.
+ * Let it ENOMEM and omit NT_FILE section which will be empty anyway.
+ */
data = kvmalloc(size, GFP_KERNEL);
if (ZERO_OR_NULL_PTR(data))
return -ENOMEM;
@@ -2257,9 +2261,13 @@ static int elf_core_dump(struct coredump_params *cprm)

dataoff = offset = roundup(offset, ELF_EXEC_PAGESIZE);

+ /*
+ * Zero vma process will get ZERO_SIZE_PTR here.
+ * Let coredump continue for register state at least.
+ */
vma_filesz = kvmalloc(array_size(sizeof(*vma_filesz), (segs - 1)),
GFP_KERNEL);
- if (ZERO_OR_NULL_PTR(vma_filesz))
+ if (!vma_filesz)
goto end_coredump;

for (i = 0, vma = first_vma(current, gate_vma); vma != NULL;
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