linux-kernel - [PATCH] x86/kexec: fix double vfree of image->elf

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Message-Id: <20230102103917.20987-1-vbabka@suse.cz>
Date:   Mon,  2 Jan 2023 11:39:17 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        patches@...ts.linux.dev, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
        Baoquan He <bhe@...hat.com>, Dave Young <dyoung@...hat.com>,
        stable@...r.kernel.org
Subject: [PATCH] x86/kexec: fix double vfree of image->elf_headers

An investigation of a "Trying to vfree() nonexistent vm area" bug
occurring in arch_kimage_file_post_load_cleanup() doing a
vfree(image->elf_headers) in our 5.14-based kernel yielded the following
double vfree() scenario, also present in mainline:

SYSCALL_DEFINE5(kexec_file_load)
  kimage_file_alloc_init()
    kimage_file_prepare_segments()
      arch_kexec_kernel_image_probe()
        kexec_image_load_default()
          kexec_bzImage64_ops.load()
            bzImage64_load()
              crash_load_segments()
                prepare_elf_headers(image, &kbuf.buffer, &kbuf.bufsz);
                image->elf_headers = kbuf.buffer;
		ret = kexec_add_buffer(&kbuf);
		if (ret) vfree((void *)image->elf_headers); // first vfree()
      if (ret) kimage_file_post_load_cleanup()
        vfree(image->elf_headers);                          // second vfree()

AFAICS the scenario is possible since v5.19 commit b3e34a47f989
("x86/kexec: fix memory leak of elf header buffer") that was marked for
stable and also was backported to our kernel.

Fix the problem by setting the pointer to NULL after the first vfree().
Also set elf_headers_sz to 0, as kimage_file_post_load_cleanup() does.

Fixes: b3e34a47f989 ("x86/kexec: fix memory leak of elf header buffer")
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
Cc: Baoquan He <bhe@...hat.com>
Cc: Dave Young <dyoung@...hat.com>
Cc: <stable@...r.kernel.org>
---
 arch/x86/kernel/crash.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 9730c88530fc..0d651c05a49e 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -403,6 +403,8 @@ int crash_load_segments(struct kimage *image)
 	ret = kexec_add_buffer(&kbuf);
 	if (ret) {
 		vfree((void *)image->elf_headers);
+		image->elf_headers = NULL;
+		image->elf_headers_sz = 0;
 		return ret;
 	}
 	image->elf_load_addr = kbuf.mem;
-- 
2.39.0