Re: malformed elf file causes readelf -e to hang forever

[Mark Wielaard <mjw at redhat dot com>]

On Mon, Jan 26, 2015 at 04:54:34PM +0100, Mark Wielaard wrote:
> > I guess it should be an error for first_global to be out of range, or at
> > least clamp it to at most syments.
> 
> And we do that in find_symtab when we find the normal symtab or the aux
> symtab. But in this case after we found the symtab we detect something
> is fishy with the string table/shdrs, so we discard the result and fall
> back to find_dynsym to get a backup symbol table through phdrs. Which
> succeeds. dynsym only has global syms, so we don't need to set
> first_global because it is initialized to zero. But... we forgot to
> clear the original first_global we found when we discarded the result...
> oops.
> 
> How does the following fix look?

I assume people thought it looked fine and pushed it to master.

> From 6e576f095e6f3bb810e6388ed8e606eacb318b67 Mon Sep 17 00:00:00 2001
> From: Mark Wielaard <mjw@redhat.com>
> Date: Mon, 26 Jan 2015 16:34:57 +0100
> Subject: [PATCH] libdwfl: Clear symtab result on error before using
>  find_dynsym fallback.
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
> 
> find_dynsym could succeed after find_symtab failed but had already set up
> symdata, syments and first_global. find_dynsym would not set or clear
> first_global since all syms in dynsym are global. Causing lots of failing
> lookups when calling __libdwfl_addrsym if first_global was some huge
> bogus value.
> 
> Reported-by: Hanno Böck <hanno@hboeck.de>
> Signed-off-by: Mark Wielaard <mjw@redhat.com>
> ---
>  libdwfl/ChangeLog              | 5 +++++
>  libdwfl/dwfl_module_getdwarf.c | 3 +++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
> index 5a97578..d40dbae 100644
> --- a/libdwfl/ChangeLog
> +++ b/libdwfl/ChangeLog
> @@ -1,3 +1,8 @@
> +2015-01-26  Mark Wielaard  <mjw@redhat.com>
> +
> +	* dwfl_module_getdwarf.c (find_symtab): Explicitly clear symdata,
> +	syments and first_global on elferr before calling find_dynsym.
> +
>  2014-12-27  Mark Wielaard  <mjw@redhat.com>
>  
>  	* dwfl_module_getsrc.c (dwfl_module_getsrc): Never match a line that
> diff --git a/libdwfl/dwfl_module_getdwarf.c b/libdwfl/dwfl_module_getdwarf.c
> index 494407d..a31898a 100644
> --- a/libdwfl/dwfl_module_getdwarf.c
> +++ b/libdwfl/dwfl_module_getdwarf.c
> @@ -1083,6 +1083,9 @@ find_symtab (Dwfl_Module *mod)
>    if (elf_strptr (mod->symfile->elf, strshndx, 0) == NULL)
>      {
>      elferr:
> +      mod->symdata = NULL;
> +      mod->syments = 0;
> +      mod->first_global = 0;
>        mod->symerr = DWFL_E (LIBELF, elf_errno ());
>        goto aux_cleanup; /* This cleans up some more and tries find_dynsym.  */
>      }
> -- 
> 1.8.3.1
>