linux-kernel - [PATCH] kexec: Fix double-free when failing to relocate the purgatory.

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Date:   Wed, 24 Aug 2016 21:05:46 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
To:     kexec@...ts.infradead.org
Cc:     Eric Biederman <ebiederm@...ssion.com>,
        Dave Young <dyoung@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>, Baoquan He <bhe@...hat.com>,
        linux-kernel@...r.kernel.org,
        Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
Subject: [PATCH] kexec: Fix double-free when failing to relocate the purgatory.

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:

[   18.112843] kexec-bzImage64: Loading purgatory failed
[   18.113257] ------------[ cut here ]------------
[   18.113263] WARNING: CPU: 1 PID: 2119 at mm/vmalloc.c:1490 __vunmap+0xc1/0xd0
[   18.113264] Trying to vfree() nonexistent vm area (ffffc90000e91000)
[   18.113367] Modules linked in:
[   18.113371] CPU: 1 PID: 2119 Comm: kexec Not tainted 4.8.0-rc3+ #5
[   18.113372] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
[   18.113373]  0000000000000000 ffff88003bbb7dc8 ffffffff8132eca8 ffff88003bbb7e18
[   18.113376]  0000000000000000 ffff88003bbb7e08 ffffffff8105f1bb 000005d281175bf8
[   18.113377]  ffffc90000e91000 0000000000000000 0000000000000001 ffff88003e5f8c00
[   18.113379] Call Trace:
[   18.113384]  [<ffffffff8132eca8>] dump_stack+0x4d/0x65
[   18.113386]  [<ffffffff8105f1bb>] __warn+0xcb/0xf0
[   18.113388]  [<ffffffff8105f22f>] warn_slowpath_fmt+0x4f/0x60
[   18.113390]  [<ffffffff81176469>] ? find_vmap_area+0x19/0x70
[   18.113393]  [<ffffffff810dbb57>] ? kimage_file_post_load_cleanup+0x47/0xb0
[   18.113394]  [<ffffffff81177451>] __vunmap+0xc1/0xd0
[   18.113396]  [<ffffffff811774ce>] vfree+0x2e/0x70
[   18.113397]  [<ffffffff810dbb6e>] kimage_file_post_load_cleanup+0x5e/0xb0
[   18.113398]  [<ffffffff810dc718>] SyS_kexec_file_load+0x448/0x680
[   18.113401]  [<ffffffff811a6834>] ? putname+0x54/0x60
[   18.113403]  [<ffffffff81195d70>] ? do_sys_open+0x190/0x1f0
[   18.113407]  [<ffffffff81824e5b>] entry_SYSCALL_64_fastpath+0x13/0x8f
[   18.113408] ---[ end trace 158bb74f5950ca2b ]---

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

Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
---
 kernel/kexec_file.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 503bc2d348e5..037c321c5618 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -887,7 +887,10 @@ int kexec_load_purgatory(struct kimage *image, unsigned long min,
 	return 0;
 out:
 	vfree(pi->sechdrs);
+	pi->sechdrs = NULL;
+
 	vfree(pi->purgatory_buf);
+	pi->purgatory_buf = NULL;
 	return ret;
 }
 
-- 
1.9.1