[PATCH v4] elf: Also try DT_RUNPATH for LD_AUDIT dlopen [BZ #28455]

[Adhemerval Zanella]

On 15/12/2021 23:06, H.J. Lu via Libc-alpha wrote:
> Changes in v4:
> 
> 1. Move the RUNPATH search for LD_AUDIT dlopen after the other RUNPATH
> search
> 2. Split one test per line and sort.
> 
> DT_RUNPATH is only used to find the immediate dependencies of the
> executable or shared object containing the DT_RUNPATH entry.  Update
> LD_AUDIT dlopen call to try the DT_RUNPATH entry of the executable.
> This partially fixes BZ #28455.

LGTM, I have only a question below.

> ---
>  elf/Makefile       | 20 +++++++++++++++++---
>  elf/dl-load.c      | 37 ++++++++++++++++++++++++++++++++-----
>  elf/tst-audit14a.c |  1 +
>  3 files changed, 50 insertions(+), 8 deletions(-)
>  create mode 100644 elf/tst-audit14a.c
> 
> diff --git a/elf/Makefile b/elf/Makefile
> index fe42caeb0e..625b1a023f 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -249,10 +249,19 @@ ifneq ($(selinux-enabled),1)
>  tests-execstack-yes = tst-execstack tst-execstack-needed tst-execstack-prog
>  endif
>  ifeq ($(have-depaudit),yes)
> -tests += tst-audit14 tst-audit15 tst-audit16
> +tests += \
> +  tst-audit14 \
> +  tst-audit14a \
> +  tst-audit15 \
> +  tst-audit16 \
> +
>  ifeq ($(run-built-tests),yes)
> -tests-special += $(objpfx)tst-audit14-cmp.out $(objpfx)tst-audit15-cmp.out \
> -		 $(objpfx)tst-audit16-cmp.out
> +tests-special += \
> +  $(objpfx)tst-audit14-cmp.out \
> +  $(objpfx)tst-audit14a-cmp.out \
> +  $(objpfx)tst-audit15-cmp.out \
> +  $(objpfx)tst-audit16-cmp.out \
> +
>  endif
>  endif
>  endif

Ok.

> @@ -1529,6 +1538,8 @@ tst-auditmany-ENV = \
>  LDFLAGS-tst-audit14 = -Wl,--audit=tst-auditlogmod-1.so
>  $(objpfx)tst-auditlogmod-1.so: $(libsupport)
>  $(objpfx)tst-audit14.out: $(objpfx)tst-auditlogmod-1.so
> +LDFLAGS-tst-audit14a = -Wl,--audit=tst-auditlogmod-1.so,--enable-new-dtags
> +$(objpfx)tst-audit14a.out: $(objpfx)tst-auditlogmod-1.so
>  LDFLAGS-tst-audit15 = \
>    -Wl,--audit=tst-auditlogmod-1.so,--depaudit=tst-auditlogmod-2.so
>  $(objpfx)tst-auditlogmod-2.so: $(libsupport)
> @@ -1555,6 +1566,9 @@ tst-audit17-ENV = LD_AUDIT=$(objpfx)tst-auditmod17.so
>  $(objpfx)tst-audit14-cmp.out: tst-audit14.exp $(objpfx)tst-audit14.out
>  	cmp $^ > $@; \
>  	$(evaluate-test)
> +$(objpfx)tst-audit14a-cmp.out: tst-audit14.exp $(objpfx)tst-audit14a.out
> +	cmp $^ > $@; \
> +	$(evaluate-test)
>  $(objpfx)tst-audit15-cmp.out: tst-audit15.exp $(objpfx)tst-audit15.out
>  	cmp $^ > $@; \
>  	$(evaluate-test)

Ok.

> diff --git a/elf/dl-load.c b/elf/dl-load.c
> index 721593135e..1c90801903 100644
> --- a/elf/dl-load.c
> +++ b/elf/dl-load.c
> @@ -2143,14 +2143,16 @@ _dl_map_object (struct link_map *loader, const char *name,
>  
>        fd = -1;
>  
> +      struct link_map *main_map = GL(dl_ns)[LM_ID_BASE]._ns_loaded;
> +      bool did_main_map;
> +
>        /* When the object has the RUNPATH information we don't use any
>  	 RPATHs.  */
>        if (loader == NULL || loader->l_info[DT_RUNPATH] == NULL)
>  	{
>  	  /* This is the executable's map (if there is one).  Make sure that
>  	     we do not look at it twice.  */
> -	  struct link_map *main_map = GL(dl_ns)[LM_ID_BASE]._ns_loaded;
> -	  bool did_main_map = false;
> +	  did_main_map = false;
>  
>  	  /* First try the DT_RPATH of the dependent object that caused NAME
>  	     to be loaded.  Then that object's dependent, and on up.  */
> @@ -2186,13 +2188,38 @@ _dl_map_object (struct link_map *loader, const char *name,
>  			loader ?: GL(dl_ns)[LM_ID_BASE]._ns_loaded,
>  			LA_SER_LIBPATH, &found_other_class);
>  
> +      /* Make sure that we do not look at RUNPATH in the executable
> +	 twice.  */
> +      did_main_map = false;
> +
>        /* Look at the RUNPATH information for this binary.  */
>        if (fd == -1 && loader != NULL
>  	  && cache_rpath (loader, &loader->l_runpath_dirs,
>  			  DT_RUNPATH, "RUNPATH"))
> -	fd = open_path (name, namelen, mode,
> -			&loader->l_runpath_dirs, &realname, &fb, loader,
> -			LA_SER_RUNPATH, &found_other_class);
> +	{
> +	  did_main_map = loader == main_map;
> +	  fd = open_path (name, namelen, mode,
> +			  &loader->l_runpath_dirs, &realname, &fb, loader,
> +			  LA_SER_RUNPATH, &found_other_class);
> +	}
> +
> +      /* When processing the lookup we may need to additionally try
> +	 DT_RUNPATH in the executable for a glibc internal dlopen call
> +	 when looking for audit modules.  */
> +      if (__glibc_unlikely (mode & __RTLD_AUDIT)
> +	  && fd == -1
> +	  && !did_main_map
> +	  && main_map != NULL

When main_map would be NULL? For namespaces different than LM_ID_BASE it
does make sense, but I think it is assumed in a lot of places that
for LM_ID_BASE that _ns_loaded is always non-NULL (even for static
linking dl-support guarantees it).

> +	  && main_map->l_type != lt_loaded)
> +	{
> +	  struct r_search_path_struct l_rpath_dirs;
> +	  l_rpath_dirs.dirs = NULL;
> +	  if (cache_rpath (main_map, &l_rpath_dirs,
> +			   DT_RUNPATH, "RUNPATH"))
> +	    fd = open_path (name, namelen, mode, &l_rpath_dirs,
> +			    &realname, &fb, loader ?: main_map,
> +			    LA_SER_RUNPATH, &found_other_class);
> +	}
>  
>        if (fd == -1)
>          {
> diff --git a/elf/tst-audit14a.c b/elf/tst-audit14a.c
> new file mode 100644
> index 0000000000..c6232eacf2
> --- /dev/null
> +++ b/elf/tst-audit14a.c
> @@ -0,0 +1 @@
> +#include "tst-audit14.c"

Add a comment that it checks the -Wl,--enable-new-dtags. Should we also
enforce --disable-new-dtags for tst-audit14 ?