Re: [Xen-devel] [PATCH 20/21] libxc: check return values from malloc

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 06/06/13 19:52, Ian Jackson wrote:
> A sufficiently malformed input to libxc (such as a malformed input ELF
> or other guest-controlled data) might cause one of libxc's malloc() to
> fail.  In this case we need to make sure we don't dereference or do
> pointer arithmetic on the result.
>
> Search for all occurrences of \b(m|c|re)alloc in libxc, and all
> functions which call them, and add appropriate error checking where
> missing.
>
> This includes the functions xc_dom_malloc*, which now print a message
> when they fail so that callers don't have to do so.
>
> The function xc_cpuid_to_str wasn't provided with a sane return value
> and has a pretty strange API, which now becomes a little stranger.
> There are no in-tree callers.
>
> This is part of the fix to a security issue, XSA-55.
>
> Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
>
> v5: This patch is new in this version of the series.
> ---
>  tools/libxc/xc_cpuid_x86.c      |   15 +++++++++++++--
>  tools/libxc/xc_dom_arm.c        |    2 ++
>  tools/libxc/xc_dom_core.c       |    9 ++++++++-
>  tools/libxc/xc_dom_elfloader.c  |    2 ++
>  tools/libxc/xc_dom_x86.c        |    3 +++
>  tools/libxc/xc_domain_restore.c |    8 ++++++++
>  tools/libxc/xc_linux_osdep.c    |    4 ++++
>  tools/libxc/xc_private.c        |    2 ++
>  tools/libxc/xenctrl.h           |    2 +-
>  9 files changed, 43 insertions(+), 4 deletions(-)
>
> diff --git a/tools/libxc/xc_cpuid_x86.c b/tools/libxc/xc_cpuid_x86.c
> index 17efc0f..7480a86 100644
> --- a/tools/libxc/xc_cpuid_x86.c
> +++ b/tools/libxc/xc_cpuid_x86.c
> @@ -590,6 +590,8 @@ static int xc_cpuid_do_domctl(
>  static char *alloc_str(void)
>  {
>      char *s = malloc(33);
> +    if ( s == NULL )
> +        return s;
>      memset(s, 0, 33);
>      return s;
>  }
> @@ -601,6 +603,8 @@ void xc_cpuid_to_str(const unsigned int *regs, char 
> **strs)
>      for ( i = 0; i < 4; i++ )
>      {
>          strs[i] = alloc_str();
> +        if ( strs[i] == NULL )
> +            continue;
>          for ( j = 0; j < 32; j++ )
>              strs[i][j] = !!((regs[i] & (1U << (31 - j)))) ? '1' : '0';
>      }
> @@ -681,7 +685,7 @@ int xc_cpuid_check(
>      const char **config,
>      char **config_transformed)
>  {
> -    int i, j;
> +    int i, j, rc;
>      unsigned int regs[4];
>  
>      memset(config_transformed, 0, 4 * sizeof(*config_transformed));
> @@ -693,6 +697,11 @@ int xc_cpuid_check(
>          if ( config[i] == NULL )
>              continue;
>          config_transformed[i] = alloc_str();
> +        if ( config_transformed[i] == NULL )
> +        {
> +            rc = -ENOMEM;
> +            goto fail_rc;
> +        }
>          for ( j = 0; j < 32; j++ )
>          {
>              unsigned char val = !!((regs[i] & (1U << (31 - j))));
> @@ -709,12 +718,14 @@ int xc_cpuid_check(
>      return 0;
>  
>   fail:
> +    rc = -EPERM;
> + fail_rc:
>      for ( i = 0; i < 4; i++ )
>      {
>          free(config_transformed[i]);
>          config_transformed[i] = NULL;
>      }
> -    return -EPERM;
> +    return rc;
>  }
>  
>  /*
> diff --git a/tools/libxc/xc_dom_arm.c b/tools/libxc/xc_dom_arm.c
> index aaf35ca..df59ffb 100644
> --- a/tools/libxc/xc_dom_arm.c
> +++ b/tools/libxc/xc_dom_arm.c
> @@ -170,6 +170,8 @@ int arch_setup_meminit(struct xc_dom_image *dom)
>      dom->shadow_enabled = 1;
>  
>      dom->p2m_host = xc_dom_malloc(dom, sizeof(xen_pfn_t) * dom->total_pages);
> +    if ( dom->p2m_host == NULL )
> +        return -EINVAL;
>  
>      /* setup initial p2m */
>      for ( pfn = 0; pfn < dom->total_pages; pfn++ )
> diff --git a/tools/libxc/xc_dom_core.c b/tools/libxc/xc_dom_core.c
> index 21a8e0d..2a9c5a2 100644
> --- a/tools/libxc/xc_dom_core.c
> +++ b/tools/libxc/xc_dom_core.c
> @@ -122,7 +122,10 @@ void *xc_dom_malloc(struct xc_dom_image *dom, size_t 
> size)
>  
>      block = malloc(sizeof(*block) + size);
>      if ( block == NULL )
> +    {
> +        DOMPRINTF("%s: allocation failed", __FUNCTION__);
>          return NULL;
> +    }
>      memset(block, 0, sizeof(*block) + size);
>      block->next = dom->memblocks;
>      dom->memblocks = block;
> @@ -137,8 +140,10 @@ void *xc_dom_malloc_page_aligned(struct xc_dom_image 
> *dom, size_t size)
>      struct xc_dom_mem *block;
>  
>      block = malloc(sizeof(*block));
> -    if ( block == NULL )
> +    if ( block == NULL ) {
> +        DOMPRINTF("%s: allocation failed", __FUNCTION__);
>          return NULL;
> +    }
>      memset(block, 0, sizeof(*block));
>      block->mmap_len = size;
>      block->mmap_ptr = mmap(NULL, block->mmap_len,
> @@ -146,6 +151,7 @@ void *xc_dom_malloc_page_aligned(struct xc_dom_image 
> *dom, size_t size)
>                             -1, 0);
>      if ( block->mmap_ptr == MAP_FAILED )
>      {
> +        DOMPRINTF("%s: mmap failed", __FUNCTION__);
>          free(block);
>          return NULL;
>      }
> @@ -202,6 +208,7 @@ void *xc_dom_malloc_filemap(struct xc_dom_image *dom,
>          close(fd);
>      if ( block != NULL )
>          free(block);
> +    DOMPRINTF("%s: failed (on file `%s')", __FUNCTION__, filename);
>      return NULL;
>  }
>  
> diff --git a/tools/libxc/xc_dom_elfloader.c b/tools/libxc/xc_dom_elfloader.c
> index ac9bb3b..ae427ef 100644
> --- a/tools/libxc/xc_dom_elfloader.c
> +++ b/tools/libxc/xc_dom_elfloader.c
> @@ -327,6 +327,8 @@ static elf_errorstatus xc_dom_parse_elf_kernel(struct 
> xc_dom_image *dom)
>          return rc;
>  
>      elf = xc_dom_malloc(dom, sizeof(*elf));
> +    if ( elf == NULL )
> +        return -1;
>      dom->private_loader = elf;
>      rc = elf_init(elf, dom->kernel_blob, dom->kernel_size);
>      xc_elf_set_logfile(dom->xch, elf, 1);
> diff --git a/tools/libxc/xc_dom_x86.c b/tools/libxc/xc_dom_x86.c
> index 8b6191d..126c0f8 100644
> --- a/tools/libxc/xc_dom_x86.c
> +++ b/tools/libxc/xc_dom_x86.c
> @@ -760,6 +760,9 @@ int arch_setup_meminit(struct xc_dom_image *dom)
>      }
>  
>      dom->p2m_host = xc_dom_malloc(dom, sizeof(xen_pfn_t) * dom->total_pages);
> +    if ( dom->p2m_host == NULL )
> +        return -EINVAL;
> +
>      if ( dom->superpages )
>      {
>          int count = dom->total_pages >> SUPERPAGE_PFN_SHIFT;
> diff --git a/tools/libxc/xc_domain_restore.c b/tools/libxc/xc_domain_restore.c
> index c7835ff..66ffc41 100644
> --- a/tools/libxc/xc_domain_restore.c
> +++ b/tools/libxc/xc_domain_restore.c
> @@ -1532,8 +1532,16 @@ int xc_domain_restore(xc_interface *xch, int io_fd, 
> uint32_t dom,
>      region_mfn = malloc(ROUNDUP(MAX_BATCH_SIZE * sizeof(xen_pfn_t), 
> PAGE_SHIFT));
>      ctx->p2m_batch = malloc(ROUNDUP(MAX_BATCH_SIZE * sizeof(xen_pfn_t), 
> PAGE_SHIFT));
>      if (!ctx->hvm && ctx->superpages)
> +    {
>          ctx->p2m_saved_batch =
>              malloc(ROUNDUP(MAX_BATCH_SIZE * sizeof(xen_pfn_t), PAGE_SHIFT));
> +        if ( ctx->p2m_saved_batch == NULL )
> +        {
> +            ERROR("saved batch memory alloc failed");
> +            errno = ENOMEM;
> +            goto out;
> +        }
> +    }

Can you not merge this NULL test into the if statement immediatly below
which does all the other NULL pointer checks?

something like (!ctx->hvm && ctx->superpages && ctx->p2m_saved_batch == NULL

~Andrew

>  
>      if ( (ctx->p2m == NULL) || (pfn_type == NULL) ||
>           (region_mfn == NULL) || (ctx->p2m_batch == NULL) )
> diff --git a/tools/libxc/xc_linux_osdep.c b/tools/libxc/xc_linux_osdep.c
> index 36832b6..73860a2 100644
> --- a/tools/libxc/xc_linux_osdep.c
> +++ b/tools/libxc/xc_linux_osdep.c
> @@ -378,6 +378,8 @@ static void *linux_privcmd_map_foreign_range(xc_interface 
> *xch, xc_osdep_handle
>  
>      num = (size + XC_PAGE_SIZE - 1) >> XC_PAGE_SHIFT;
>      arr = calloc(num, sizeof(xen_pfn_t));
> +    if ( arr == NULL )
> +        return NULL;
>  
>      for ( i = 0; i < num; i++ )
>          arr[i] = mfn + i;
> @@ -402,6 +404,8 @@ static void 
> *linux_privcmd_map_foreign_ranges(xc_interface *xch, xc_osdep_handle
>      num_per_entry = chunksize >> XC_PAGE_SHIFT;
>      num = num_per_entry * nentries;
>      arr = calloc(num, sizeof(xen_pfn_t));
> +    if ( arr == NULL )
> +        return NULL;
>  
>      for ( i = 0; i < nentries; i++ )
>          for ( j = 0; j < num_per_entry; j++ )
> diff --git a/tools/libxc/xc_private.c b/tools/libxc/xc_private.c
> index e891cc8..acaf9e0 100644
> --- a/tools/libxc/xc_private.c
> +++ b/tools/libxc/xc_private.c
> @@ -771,6 +771,8 @@ const char *xc_strerror(xc_interface *xch, int errcode)
>          errbuf = pthread_getspecific(errbuf_pkey);
>          if (errbuf == NULL) {
>              errbuf = malloc(XS_BUFSIZE);
> +            if ( errbuf == NULL )
> +                return "(failed to allocate errbuf)";
>              pthread_setspecific(errbuf_pkey, errbuf);
>          }
>  
> diff --git a/tools/libxc/xenctrl.h b/tools/libxc/xenctrl.h
> index c024af4..f6f4ceb 100644
> --- a/tools/libxc/xenctrl.h
> +++ b/tools/libxc/xenctrl.h
> @@ -1829,7 +1829,7 @@ int xc_cpuid_set(xc_interface *xch,
>  int xc_cpuid_apply_policy(xc_interface *xch,
>                            domid_t domid);
>  void xc_cpuid_to_str(const unsigned int *regs,
> -                     char **strs);
> +                     char **strs); /* some strs[] may be NULL if ENOMEM */
>  int xc_mca_op(xc_interface *xch, struct xen_mc *mc);
>  #endif
>  


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