[RFC,v8,11/20] Compare loaded DSOs by file ID and check for DF_GNU_1_UNIQUE

  If _dl_map_object_from_fd finds that a DSO it was asked to
load into a non-base namespace is already loaded (into the
main namespace) and is flagged DF_GNU_1_UNIQUE then it should
return that DSO's link map entry.

In such cases _dl_open_worker must notice that this has
happened and dontinue down the link map proxy generation
path instead of normal link map entry preparation.
---
 elf/dl-load.c | 26 ++++++++++++++++++++++++++
 elf/dl-open.c | 10 ++++++++++
 2 files changed, 36 insertions(+)
  

On 09/02/2021 14:18, Vivek Das Mohapatra via Libc-alpha wrote:
> If _dl_map_object_from_fd finds that a DSO it was asked to
> load into a non-base namespace is already loaded (into the
> main namespace) and is flagged DF_GNU_1_UNIQUE then it should
> return that DSO's link map entry.
> 
> In such cases _dl_open_worker must notice that this has
> happened and dontinue down the link map proxy generation

s/dontinue/continue.

> path instead of normal link map entry preparation.
> ---
>  elf/dl-load.c | 26 ++++++++++++++++++++++++++
>  elf/dl-open.c | 10 ++++++++++
>  2 files changed, 36 insertions(+)
> 
> diff --git a/elf/dl-load.c b/elf/dl-load.c
> index 2a01ab7ad2..780bca99e8 100644
> --- a/elf/dl-load.c
> +++ b/elf/dl-load.c
> @@ -1020,6 +1020,32 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
>      }
>  #endif
>  
> +  /* DSOs in the main namespace which are flagged DF_GNU_1_UNIQUE should only
> +     be opened into the main namespace. Other namespaces should only get
> +     proxies.  */
> +  if (__glibc_unlikely (nsid != LM_ID_BASE))
> +    {
> +      /* Check base ns to see if the name matched another already loaded.  */
> +      for (l = GL(dl_ns)[LM_ID_BASE]._ns_loaded; l != NULL; l = l->l_next)
> +        if (!l->l_removed && _dl_file_id_match_p (&l->l_file_id, &id))
> +          {
> +            if (!(l->l_gnu_flags_1 & DF_GNU_1_UNIQUE))
> +              continue;
> +
> +            /* Already loaded. Bump its reference count and return it.  */
> +            __close_nocancel (fd);
> +
> +            /* If the name is not listed for this object add it.  */
> +            free (realname);
> +            add_name_to_object (l, name);
> +
> +            /* NOTE: It is important that our caller picks up on the fact
> +               that we have NOT returned an object in the requested namespace
> +               and handles the proxying correctly */

Missing period and double space before comment end.

> +            return l;
> +          }
> +    }
> +
>    if (mode & RTLD_NOLOAD)
>      {
>        /* We are not supposed to load the object unless it is already
> diff --git a/elf/dl-open.c b/elf/dl-open.c
> index 096aa4c680..441b8b1330 100644
> --- a/elf/dl-open.c
> +++ b/elf/dl-open.c
> @@ -561,6 +561,16 @@ dl_open_worker (void *a)
>        return;
>      }
>  
> +  /* If we are trying to load a DF_GNU_1_UNIQUE flagged DSO which was
> +     NOT ALREADY LOADED (or not loaded with the name we are using) then
> +     _dl_map_object will have returned an instance from the main namespace.
> +     We need to detect this and set up the RTLD_SHARED flags.  */
> +  if (__glibc_unlikely(args->nsid != LM_ID_BASE && new->l_ns == LM_ID_BASE))

Space before '(' 

> +    {
> +      want_proxy = RTLD_SHARED;
> +      mode |= RTLD_SHARED;
> +    }
> +
>    /* If we want proxy and we get this far then the entry in ‘new’ will
>       be in the main namespace: we should revert to the main namespace code
>       path(s), but remember the namespace we want the proxy to be in.  */
>