[v2] grub-file: fix segmentation fault

22.11.2016 10:10, Michael Chang пишет:
> On Fri, Nov 18, 2016 at 11:50:25AM +0300, Andrei Borzenkov wrote:

>> Hmm ... I must admit I am confused how we can get NULL here. Filters

>> are called after primary file->name is set and each filter copies

>> previous struct file, which means returned file will inherit pointer

>> to the same file name.

> 

> No. I don't think so. Looking into gzio or xzio file filters they did not copy

> original handle to new allocated one. And the new handle gets initialized

> without file->name being set from original one. The new handle then returned

> to upper file layer with file->name being null.

> 


Right, I was mistaken.

>> Anyway, exactly because filters themselves do not free file->name this

>> patch means memory leak.

> 

> Same reason above, as long as the filters did not allocate it, they did not

> need to free.

> 


Yes, but your patch allocates copy of name and (some) filters set it to
NULL so it is leaked.

What about attached patch? It does not increase size of kernel.

I am not thrilled as it does require more discipline from filter author.
OTOH we may find some way to consolidate boilerplate later.

@Dann, this also solves your concerns about layering violation in
progress module as side effect. Could you test this patch? Thank you!

>> Michael, could you provide reproducer for it?

> 

> I can still reproduce the segfault on latest git HEAD. Here is kernel image

> attached to reproduce the problem with:

> 

>  grub/build-xen # ./grub-file --is-x86_64-xen-domu /boot/vmlinux-4.8.4-1-default.gz

>  Segmentation fault (core dumped)

> 

> Thanks,

> Michael

>
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On Tue, Nov 22, 2016 at 09:39:43PM +0300, Andrei Borzenkov wrote:
> 22.11.2016 10:10, Michael Chang пишет:
> 
> What about attached patch? It does not increase size of kernel.

Just some nitpicks in comments and a potential leak in fail path (See below),
otherwise LGTM.

> 
> I am not thrilled as it does require more discipline from filter author.
> OTOH we may find some way to consolidate boilerplate later.

Yes, that's also why I tend to not touch the filter but trying to paper over it
on the parent's side, to be less frustrated to the filter authors.

> 
> @Dann, this also solves your concerns about layering violation in
> progress module as side effect. Could you test this patch? Thank you!

I think this may deserve a separate patch (in file.c and progress.c) as it did
not fixed by the segfault problem here. But that's all up to you, as
consolidating all file->name related fix in one patch is nothing wrong.

> From: Andrei Borzenkov <arvidjaar@gmail.com>
> Subject: [PATCH] file: make sure file name is set when filters are used
> 
> In grub_file_open the file handle returned by file filters has no file->name
> set which leads to segmentation fault later referenced by grub_elf_file. This
> patch tries to fix the problem.
> 
>  gdb --args ./grub-file --is-x86_64-xen-domu /boot/vmlinux-4.1.12-1-default.gz
> 
>  (gdb) bt
>  #0  0x000000000047597e in grub_strlen (s=0x0) at ../grub-core/kern/misc.c:558
>  #1  0x00000000004757e2 in grub_strdup (s=0x0) at ../grub-core/kern/misc.c:463
>  #2  0x0000000000406418 in grub_elf_file (file=0x6dfb50, filename=0x0) at ../grub-core/kern/elf.c:89
>  #3  0x00000000004043b3 in grub_xen_file (file=0x6dfb50) at ../grub-core/loader/i386/xen_file.c:29
>  #4  0x0000000000403930 in grub_cmd_file (ctxt=0x7fffffffe120, argc=1, args=0x6dfa00) at ../grub-core/commands/file.c:425
>  #5  0x000000000047e178 in grub_extcmd_dispatcher (cmd=0x6df730, argc=2, args=0x6ddfb0, script=0x0) at ../grub-core/commands/extcmd.c:54
>  #6  0x000000000047e1d7 in grub_extcmd_dispatch (cmd=0x6df730, argc=2, args=0x6ddfb0) at ../grub-core/commands/extcmd.c:67
>  #7  0x0000000000402945 in main (argc=3, argv=0x7fffffffe2e8) at ../util/grub-file.c:102
>  (gdb) frame 3
>  #3  0x00000000004043b3 in grub_xen_file (file=0x6dfb50) at ../grub-core/loader/i386/xen_file.c:29
>  29        elf = grub_elf_file (file, file->name);
> 
> Initialize file->name early and make sure it is set in file structure returned
> by each filter. Note that each filter must set it to NULL in its ->close method
> to avoid double free.
> 
> It also makes redundant special case for net in progress module, because now file
> name is set also for net files.
> 
> Reported by: Michael Chang <mchang@suse.com>
> 
> ---
>  grub-core/commands/verify.c | 1 +
>  grub-core/io/bufio.c        | 3 +++
>  grub-core/io/gzio.c         | 2 ++
>  grub-core/io/lzopio.c       | 2 ++
>  grub-core/io/offset.c       | 3 +++
>  grub-core/io/xzio.c         | 2 ++
>  grub-core/kern/file.c       | 5 ++---
>  grub-core/lib/progress.c    | 7 +------
>  8 files changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/grub-core/commands/verify.c b/grub-core/commands/verify.c
> index 67cb1c7..a959929 100644
> --- a/grub-core/commands/verify.c
> +++ b/grub-core/commands/verify.c
> @@ -845,6 +845,7 @@ verified_close (struct grub_file *file)
>  
>    /* device and name are freed by parent */
>    file->device = 0;
> +  /* Must set to NULL to prevent double free in grub_file_close */

As long as the comment is intended to make things more obvious, I'd suggest to
address again it's for "parent's" grub_file_close and be more in line with
previous comment has claimed.

Same applies for all similar comments below.

>    file->name = 0;
>  
>    return grub_errno;
> diff --git a/grub-core/io/bufio.c b/grub-core/io/bufio.c
> index 2243827..3a8a53c 100644
> --- a/grub-core/io/bufio.c
> +++ b/grub-core/io/bufio.c
> @@ -72,6 +72,7 @@ grub_bufio_open (grub_file_t io, int size)
>    bufio->block_size = size;
>  
>    file->device = io->device;
> +  file->name = io->name;
>    file->size = io->size;
>    file->data = bufio;
>    file->fs = &grub_bufio_fs;
> @@ -191,6 +192,8 @@ grub_bufio_close (grub_file_t file)
>    grub_free (bufio);
>  
>    file->device = 0;
> +  /* Must set to NULL to prevent double free in grub_file_close */
> +  file->name = 0;
>  
>    return grub_errno;
>  }
> diff --git a/grub-core/io/gzio.c b/grub-core/io/gzio.c
> index 0f2ea6b..17dcbe3 100644
> --- a/grub-core/io/gzio.c
> +++ b/grub-core/io/gzio.c
> @@ -1144,6 +1144,7 @@ grub_gzio_open (grub_file_t io, const char *name __attribute__ ((unused)))
>    gzio->file = io;
>  
>    file->device = io->device;
> +  file->name = io->name;
>    file->data = gzio;
>    file->fs = &grub_gzio_fs;
>    file->not_easily_seekable = 1;
> @@ -1291,6 +1292,7 @@ grub_gzio_close (grub_file_t file)
>  
>    /* No need to close the same device twice.  */
>    file->device = 0;
> +  /* Must set to NULL to prevent double free in grub_file_close */
>    file->name = 0;
>  
>    return grub_errno;
> diff --git a/grub-core/io/lzopio.c b/grub-core/io/lzopio.c
> index 7559c6c..52acde4 100644
> --- a/grub-core/io/lzopio.c
> +++ b/grub-core/io/lzopio.c
> @@ -427,6 +427,7 @@ grub_lzopio_open (grub_file_t io,
>    lzopio->file = io;
>  
>    file->device = io->device;
> +  file->name = io->name;
>    file->data = lzopio;
>    file->fs = &grub_lzopio_fs;
>    file->size = GRUB_FILE_SIZE_UNKNOWN;
> @@ -523,6 +524,7 @@ grub_lzopio_close (grub_file_t file)
>  
>    /* Device must not be closed twice.  */
>    file->device = 0;
> +  /* Must set to NULL to prevent double free in grub_file_close */
>    file->name = 0;
>    return grub_errno;
>  }
> diff --git a/grub-core/io/offset.c b/grub-core/io/offset.c
> index ebed0eb..1de192e 100644
> --- a/grub-core/io/offset.c
> +++ b/grub-core/io/offset.c
> @@ -46,6 +46,8 @@ grub_offset_close (grub_file_t file)
>  
>    /* No need to close the same device twice.  */
>    file->device = 0;
> +  /* Must set to NULL to prevent double free in grub_file_close */
> +  file->name = 0;
>  
>    return 0;
>  }
> @@ -88,6 +90,7 @@ grub_file_offset_open (grub_file_t parent, grub_off_t start, grub_off_t size)
>    off_data->parent = parent;
>  
>    off_file->device = parent->device;
> +  off_file->name = parent->name;
>    off_file->data = off_data;
>    off_file->fs = &grub_offset_fs;
>    off_file->size = size;
> diff --git a/grub-core/io/xzio.c b/grub-core/io/xzio.c
> index a3536ad..cdf6cef 100644
> --- a/grub-core/io/xzio.c
> +++ b/grub-core/io/xzio.c
> @@ -189,6 +189,7 @@ grub_xzio_open (grub_file_t io,
>    xzio->file = io;
>  
>    file->device = io->device;
> +  file->name = io->name;
>    file->data = xzio;
>    file->fs = &grub_xzio_fs;
>    file->size = GRUB_FILE_SIZE_UNKNOWN;
> @@ -319,6 +320,7 @@ grub_xzio_close (grub_file_t file)
>  
>    /* Device must not be closed twice.  */
>    file->device = 0;
> +  /* Must set to NULL to prevent double free in grub_file_close */
>    file->name = 0;
>    return grub_errno;
>  }
> diff --git a/grub-core/kern/file.c b/grub-core/kern/file.c
> index 668f893..dd6c28a 100644
> --- a/grub-core/kern/file.c
> +++ b/grub-core/kern/file.c
> @@ -88,6 +88,8 @@ grub_file_open (const char *name)
>      goto fail;
>  
>    file->device = device;
> +  file->name = grub_strdup (name);
> +  grub_errno = GRUB_ERR_NONE;
>  
>    /* In case of relative pathnames and non-Unix systems (like Windows)
>     * name of host files may not start with `/'. Blocklists for host files
> @@ -111,9 +113,6 @@ grub_file_open (const char *name)
>    if ((file->fs->open) (file, file_name) != GRUB_ERR_NONE)
>      goto fail;
>  
> -  file->name = grub_strdup (name);
> -  grub_errno = GRUB_ERR_NONE;
> -

Well.. I think file->name now has to be free also in the "goto fail" path.

Thanks,
Michael

>    for (filter = 0; file && filter < ARRAY_SIZE (grub_file_filters_enabled);
>         filter++)
>      if (grub_file_filters_enabled[filter])
> diff --git a/grub-core/lib/progress.c b/grub-core/lib/progress.c
> index 4b7cbbc..c8efdb1 100644
> --- a/grub-core/lib/progress.c
> +++ b/grub-core/lib/progress.c
> @@ -77,12 +77,7 @@ grub_file_progress_hook_real (grub_disk_addr_t sector __attribute__ ((unused)),
>  	percent = grub_divmod64 (100 * file->progress_offset,
>  				 file->size, 0);
>  
> -      /* grub_net_fs_open() saves off partial file structure before name is initialized.
> -         It already saves passed file name in net structure so just use it in this case.
> -       */
> -      if (file->device->net)
> -	partial_file_name = grub_strrchr (file->device->net->name, '/');
> -      else if (file->name) /* grub_file_open() may leave it as NULL */
> +      if (file->name) /* grub_file_open() may leave it as NULL */
>  	partial_file_name = grub_strrchr (file->name, '/');
>        else
>  	partial_file_name = NULL;



> -- 
> tg: (c9a8d03..) u/file-filter-filename (depends on: master)

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