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From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
To: libc-alpha@sourceware.org, Szabolcs Nagy <szabolcs.nagy@arm.com>
Subject: Re: [PATCH v2 04/14] elf: Refactor _dl_update_slotinfo to avoid use after free
Date: Wed, 14 Apr 2021 15:20:41 -0300	[thread overview]
Message-ID: <5f8fd117-3b6a-f5ec-2614-b02878e7b7b6@linaro.org> (raw)
In-Reply-To: <3237824fb057632817a8de508d1fcb1f2e6f5c7e.1618301209.git.szabolcs.nagy@arm.com>



On 13/04/2021 05:18, Szabolcs Nagy via Libc-alpha wrote:
> map is not valid to access here because it can be freed by a concurrent
> dlclose: during tls access (via __tls_get_addr) _dl_update_slotinfo is
> called without holding dlopen locks. So don't check the modid of map.
> 
> The map == 0 and map != 0 code paths can be shared (avoiding the dtv
> resize in case of map == 0 is just an optimization: larger dtv than
> necessary would be fine too).
> 
> --
> v2:
> - commit message update

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  elf/dl-tls.c | 21 +++++----------------
>  1 file changed, 5 insertions(+), 16 deletions(-)
> 
> diff --git a/elf/dl-tls.c b/elf/dl-tls.c
> index 24d00c14ef..f8b32b3ecb 100644
> --- a/elf/dl-tls.c
> +++ b/elf/dl-tls.c
> @@ -743,6 +743,8 @@ _dl_update_slotinfo (unsigned long int req_modid)
>  	{
>  	  for (size_t cnt = total == 0 ? 1 : 0; cnt < listp->len; ++cnt)
>  	    {
> +	      size_t modid = total + cnt;
> +
>  	      size_t gen = listp->slotinfo[cnt].gen;
>  
>  	      if (gen > new_gen)
> @@ -758,25 +760,12 @@ _dl_update_slotinfo (unsigned long int req_modid)
>  
>  	      /* If there is no map this means the entry is empty.  */
>  	      struct link_map *map = listp->slotinfo[cnt].map;
> -	      if (map == NULL)
> -		{
> -		  if (dtv[-1].counter >= total + cnt)
> -		    {
> -		      /* If this modid was used at some point the memory
> -			 might still be allocated.  */
> -		      free (dtv[total + cnt].pointer.to_free);
> -		      dtv[total + cnt].pointer.val = TLS_DTV_UNALLOCATED;
> -		      dtv[total + cnt].pointer.to_free = NULL;
> -		    }
> -
> -		  continue;
> -		}
> -
>  	      /* Check whether the current dtv array is large enough.  */
> -	      size_t modid = map->l_tls_modid;
> -	      assert (total + cnt == modid);
>  	      if (dtv[-1].counter < modid)
>  		{
> +		  if (map == NULL)
> +		    continue;
> +
>  		  /* Resize the dtv.  */
>  		  dtv = _dl_resize_dtv (dtv);
>  
> 

  reply	other threads:[~2021-04-14 18:20 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-13  8:17 [PATCH v2 00/14] Dynamic TLS related data race fixes Szabolcs Nagy
2021-04-13  8:18 ` [PATCH v2 01/14] elf: Fix a DTV setup issue [BZ #27136] Szabolcs Nagy
2021-04-13  8:36   ` Andreas Schwab
2021-04-13  9:35     ` Szabolcs Nagy
2021-04-13 10:22       ` Andreas Schwab
2021-04-13 10:34         ` Szabolcs Nagy
2021-04-13 10:51           ` Andreas Schwab
2021-04-13  8:18 ` [PATCH v2 02/14] elf: Add a DTV setup test " Szabolcs Nagy
2021-04-14 18:06   ` Adhemerval Zanella
2021-04-15  9:53     ` Szabolcs Nagy
2021-04-13  8:18 ` [PATCH v2 03/14] elf: Fix comments and logic in _dl_add_to_slotinfo Szabolcs Nagy
2021-04-14 18:12   ` Adhemerval Zanella
2021-04-13  8:18 ` [PATCH v2 04/14] elf: Refactor _dl_update_slotinfo to avoid use after free Szabolcs Nagy
2021-04-14 18:20   ` Adhemerval Zanella [this message]
2021-04-13  8:19 ` [PATCH v2 05/14] elf: Fix data races in pthread_create and TLS access [BZ #19329] Szabolcs Nagy
2021-04-15 17:44   ` Adhemerval Zanella
2021-04-13  8:19 ` [PATCH v2 06/14] elf: Use relaxed atomics for racy accesses " Szabolcs Nagy
2021-04-15 18:21   ` Adhemerval Zanella
2021-04-16  9:12     ` Szabolcs Nagy
2021-05-11  2:56       ` Carlos O'Donell
2021-05-11  9:31         ` Szabolcs Nagy
2021-05-11 16:19           ` Szabolcs Nagy
2021-05-12 20:33           ` Carlos O'Donell
2021-04-13  8:19 ` [PATCH v2 07/14] elf: Add test case for " Szabolcs Nagy
2021-04-15 19:21   ` Adhemerval Zanella
2021-04-13  8:20 ` [PATCH v2 08/14] elf: Fix DTV gap reuse logic [BZ #27135] Szabolcs Nagy
2021-04-15 19:45   ` Adhemerval Zanella
2021-06-24  9:48   ` Florian Weimer
2021-06-24 12:27     ` Florian Weimer
2021-06-24 12:57       ` Adhemerval Zanella
2021-06-24 14:20         ` Florian Weimer
2021-06-24 18:58       ` Szabolcs Nagy
2021-04-13  8:20 ` [PATCH v2 09/14] x86_64: Avoid lazy relocation of tlsdesc [BZ #27137] Szabolcs Nagy
2021-04-13 14:02   ` H.J. Lu
2021-04-13  8:20 ` [PATCH v2 10/14] i386: " Szabolcs Nagy
2021-04-13 14:02   ` H.J. Lu
2021-04-13  8:21 ` [PATCH v2 11/14] x86_64: Remove lazy tlsdesc relocation related code Szabolcs Nagy
2021-04-13 14:03   ` H.J. Lu
2021-04-13  8:21 ` [PATCH v2 12/14] i386: " Szabolcs Nagy
2021-04-13 14:04   ` H.J. Lu
2021-04-13  8:21 ` [PATCH v2 13/14] elf: " Szabolcs Nagy
2021-04-15 19:52   ` Adhemerval Zanella
2021-04-13  8:21 ` [PATCH v2 14/14] RFC elf: Fix slow tls access after dlopen [BZ #19924] Szabolcs Nagy
2022-09-16  9:54   ` Carlos O'Donell

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