Patch "kexec: fix double-free when failing to relocate the purgatory" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

kexec: fix double-free when failing to relocate the purgatory

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kexec-fix-double-free-when-failing-to-relocate-the-purgatory.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Thiago Jung Bauermann <[email protected]>
Date: Thu, 1 Sep 2016 16:14:44 -0700
Subject: kexec: fix double-free when failing to relocate the purgatory

From: Thiago Jung Bauermann <[email protected]>

commit 070c43eea5043e950daa423707ae3c77e2f48edb upstream.

If kexec_apply_relocations fails, kexec_load_purgatory frees pi->sechdrs and pi->purgatory_buf. This is redundant, because in case of error kimage_file_prepare_segments calls kimage_file_post_load_cleanup, which will also free those buffers.

This causes two warnings like the following, one for pi->sechdrs and the other for pi->purgatory_buf:

kexec-bzImage64: Loading purgatory failed

  ------------[ cut here ]------------
  WARNING: CPU: 1 PID: 2119 at mm/vmalloc.c:1490 __vunmap+0xc1/0xd0
  Trying to vfree() nonexistent vm area (ffffc90000e91000)
  Modules linked in:
  CPU: 1 PID: 2119 Comm: kexec Not tainted 4.8.0-rc3+ #5
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
  Call Trace:
    dump_stack+0x4d/0x65
    __warn+0xcb/0xf0
    warn_slowpath_fmt+0x4f/0x60
    ? find_vmap_area+0x19/0x70
    ? kimage_file_post_load_cleanup+0x47/0xb0
    __vunmap+0xc1/0xd0
    vfree+0x2e/0x70
    kimage_file_post_load_cleanup+0x5e/0xb0
    SyS_kexec_file_load+0x448/0x680
    ? putname+0x54/0x60
    ? do_sys_open+0x190/0x1f0
    entry_SYSCALL_64_fastpath+0x13/0x8f
  ---[ end trace 158bb74f5950ca2b ]---

Fix by setting pi->sechdrs an pi->purgatory_buf to NULL, since vfree won't try to free a NULL pointer.

---
 kernel/kexec_file.c |    3 +++
 1 file changed, 3 insertions(+)

@@ -934,7 +934,10 @@ int kexec_load_purgatory(struct kimage *
 	return 0;
 out:
 	vfree(pi->sechdrs);
+	pi->sechdrs = NULL;
+
 	vfree(pi->purgatory_buf);
+	pi->purgatory_buf = NULL;
 	return ret;
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/kexec-fix-double-free-when-failing-to-relocate-the-purgatory.patch