On Tue, Apr 20, 2021 at 12:20 AM Lakshmi Ramasubramanian
[off-list ref] wrote:

On 4/19/21 10:00 PM, Dan Carpenter wrote:

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On Tue, Apr 20, 2021 at 09:30:16AM +1000, Michael Ellerman wrote:

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Lakshmi Ramasubramanian [off-list ref] writes:

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On 4/16/21 2:05 AM, Michael Ellerman wrote:

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Daniel Axtens [off-list ref] writes:

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On 4/15/21 12:14 PM, Lakshmi Ramasubramanian wrote:

Sorry - missed copying device-tree and powerpc mailing lists.

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There are a few "goto out;" statements before the local variable "fdt"
is initialized through the call to of_kexec_alloc_and_setup_fdt() in
elf64_load(). This will result in an uninitialized "fdt" being passed
to kvfree() in this function if there is an error before the call to
of_kexec_alloc_and_setup_fdt().

Initialize the local variable "fdt" to NULL.

I'm a huge fan of initialising local variables! But I'm struggling to
find the code path that will lead to an uninit fdt being returned...

The out label reads in part:

  /* Make kimage_file_post_load_cleanup free the fdt buffer for us. */
  return ret ? ERR_PTR(ret) : fdt;

As far as I can tell, any time we get a non-zero ret, we're going to
return an error pointer rather than the uninitialised value...

As Dan pointed out, the new code is in linux-next.

I have copied the new one below - the function doesn't return fdt, but
instead sets it in the arch specific field (please see the link to the
updated elf_64.c below).

https://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git/tree/arch/powerpc/kexec/elf_64.c?h=for-next

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(btw, it does look like we might leak fdt if we have an error after we
successfully kmalloc it.)

Am I missing something? Can you link to the report for the kernel test
robot or from Dan?

/*
           * Once FDT buffer has been successfully passed to
kexec_add_buffer(),
           * the FDT buffer address is saved in image->arch.fdt. In that
case,
           * the memory cannot be freed here in case of any other error.
           */
          if (ret && !image->arch.fdt)
                  kvfree(fdt);

          return ret ? ERR_PTR(ret) : NULL;

In case of an error, the memory allocated for fdt is freed unless it has
already been passed to kexec_add_buffer().

It feels like the root of the problem is that the kvfree of fdt is in
the wrong place. It's only allocated later in the function, so the error
path should reflect that. Something like the patch below.

cheers

diff --git a/arch/powerpc/kexec/elf_64.c b/arch/powerpc/kexec/elf_64.c
index 5a569bb51349..02662e72c53d 100644
--- a/arch/powerpc/kexec/elf_64.c
+++ b/arch/powerpc/kexec/elf_64.c

@@ -114,7 +114,7 @@ static void *elf64_load(struct kimage *image, char *kernel_buf,
     ret = setup_new_fdt_ppc64(image, fdt, initrd_load_addr,
                               initrd_len, cmdline);
     if (ret)
-            goto out;
+            goto out_free_fdt;

     fdt_pack(fdt);

@@ -125,7 +125,7 @@ static void *elf64_load(struct kimage *image, char *kernel_buf,
     kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
     ret = kexec_add_buffer(&kbuf);
     if (ret)
-            goto out;
+            goto out_free_fdt;

     /* FDT will be freed in arch_kimage_file_post_load_cleanup */
     image->arch.fdt = fdt;

@@ -140,18 +140,14 @@ static void *elf64_load(struct kimage *image, char *kernel_buf,
     if (ret)
             pr_err("Error setting up the purgatory.\n");

+    goto out;

This will leak.  It would need to be something like:

      if (ret) {
              pr_err("Error setting up the purgatory.\n");
              goto out_free_fdt;
      }

Once "fdt" buffer is successfully passed to kexec_add_buffer() it cannot
be freed here - it will be freed when the kexec cleanup function is called.

That may be the case currently, but really if a function returns an
error it should have undone anything it did like memory allocations. I
don't think you should do that to fix this issue, but it would be a
good clean-up.

Rob