[PATCH] coredump: fix spam with zero VMA process

From: Alexey Dobriyan
Date: Tue Apr 10 2018 - 14:04:04 EST


Nobody ever tried to self destruct by unmapping whole address space at once:

munmap((void *)0, (1ULL << 47) - 4096);

Doing this produces 2 warnings for zero-length vmalloc allocations:

a.out[1353]: segfault at 7f80bcc4b757 ip 00007f80bcc4b757 sp 00007fff683939b8 error 14
a.out: vmalloc: allocation failure: 0 bytes, mode:0xcc0(GFP_KERNEL), nodemask=(null)
...
a.out: vmalloc: allocation failure: 0 bytes, mode:0xcc0(GFP_KERNEL), nodemask=(null)
...

Fix is to switch to kvmalloc().

Steps to reproduce:

// vsyscall=none
#include <sys/mman.h>
#include <sys/resource.h>
int main(void)
{
setrlimit(RLIMIT_CORE, &(struct rlimit){RLIM_INFINITY, RLIM_INFINITY});
munmap((void *)0, (1ULL << 47) - 4096);
return 0;
}

Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
---

fs/binfmt_elf.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)

--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1608,8 +1608,8 @@ static int fill_files_note(struct memelfnote *note)
if (size >= MAX_FILE_NOTE_SIZE) /* paranoia check */
return -EINVAL;
size = round_up(size, PAGE_SIZE);
- data = vmalloc(size);
- if (!data)
+ data = kvmalloc(size, GFP_KERNEL);
+ if (ZERO_OR_NULL_PTR(data))
return -ENOMEM;

start_end_ofs = data + 2;
@@ -1626,7 +1626,7 @@ static int fill_files_note(struct memelfnote *note)
filename = file_path(file, name_curpos, remaining);
if (IS_ERR(filename)) {
if (PTR_ERR(filename) == -ENAMETOOLONG) {
- vfree(data);
+ kvfree(data);
size = size * 5 / 4;
goto alloc;
}
@@ -1919,7 +1919,7 @@ static void free_note_info(struct elf_note_info *info)
kfree(t);
}
kfree(info->psinfo.data);
- vfree(info->files.data);
+ kvfree(info->files.data);
}

#else
@@ -2135,7 +2135,7 @@ static void free_note_info(struct elf_note_info *info)

/* Free data possibly allocated by fill_files_note(): */
if (info->notes_files)
- vfree(info->notes_files->data);
+ kvfree(info->notes_files->data);

kfree(info->prstatus);
kfree(info->psinfo);
@@ -2281,8 +2281,8 @@ static int elf_core_dump(struct coredump_params *cprm)

if (segs - 1 > ULONG_MAX / sizeof(*vma_filesz))
goto end_coredump;
- vma_filesz = vmalloc((segs - 1) * sizeof(*vma_filesz));
- if (!vma_filesz)
+ vma_filesz = kvmalloc((segs - 1) * sizeof(*vma_filesz), GFP_KERNEL);
+ if (ZERO_OR_NULL_PTR(vma_filesz))
goto end_coredump;

for (i = 0, vma = first_vma(current, gate_vma); vma != NULL;
@@ -2389,7 +2389,7 @@ static int elf_core_dump(struct coredump_params *cprm)
cleanup:
free_note_info(&info);
kfree(shdr4extnum);
- vfree(vma_filesz);
+ kvfree(vma_filesz);
kfree(phdr4note);
kfree(elf);
out: