Re: [PATCH v2 3/6] elf: Fix failure handling in _dl_map_object_from_fd

From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
To: Szabolcs Nagy <szabolcs.nagy@arm.com>, libc-alpha@sourceware.org
Cc: Mark Rutland <mark.rutland@arm.com>,
	kernel-hardening@lists.openwall.com,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-kernel@vger.kernel.org,
	Jeremy Linton <jeremy.linton@arm.com>,
	Mark Brown <broonie@kernel.org>,
	Topi Miettinen <toiwoton@gmail.com>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 3/6] elf: Fix failure handling in _dl_map_object_from_fd
Date: Thu, 10 Dec 2020 15:25:12 -0300	[thread overview]
Message-ID: <1525639f-560f-2677-b1cb-f904b3552c71@linaro.org> (raw)
In-Reply-To: <8ebf571196dd499c61983dbf53c94c68ebd458cc.1606319495.git.szabolcs.nagy@arm.com>

On 27/11/2020 10:20, Szabolcs Nagy via Libc-alpha wrote:
> There are many failure paths that call lose to do local cleanups
> in _dl_map_object_from_fd, but it did not clean everything.
> 
> Handle l_phdr, l_libname and mapped segments in the common failure
> handling code.
> 
> There are various bits that may not be cleaned properly on failure
> (e.g. executable stack, tlsid, incomplete dl_map_segments).
> ---
>  elf/dl-load.c | 24 +++++++++++++++---------
>  1 file changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/elf/dl-load.c b/elf/dl-load.c
> index 21e55deb19..9c71b7562c 100644
> --- a/elf/dl-load.c
> +++ b/elf/dl-load.c
> @@ -914,8 +914,15 @@ lose (int code, int fd, const char *name, char *realname, struct link_map *l,
>    /* The file might already be closed.  */
>    if (fd != -1)
>      (void) __close_nocancel (fd);
> +  if (l != NULL && l->l_map_start != 0)
> +    _dl_unmap_segments (l);
>    if (l != NULL && l->l_origin != (char *) -1l)
>      free ((char *) l->l_origin);
> +  if (l != NULL && !l->l_libname->dont_free)
> +    free (l->l_libname);
> +  if (l != NULL && l->l_phdr_allocated)
> +    free ((void *) l->l_phdr);
> +
>    free (l);
>    free (realname);
>  
> @@ -1256,7 +1263,11 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
>      errstring = _dl_map_segments (l, fd, header, type, loadcmds, nloadcmds,
>  				  maplength, has_holes, loader);
>      if (__glibc_unlikely (errstring != NULL))
> -      goto call_lose;
> +      {
> +	/* Mappings can be in an inconsistent state: avoid unmap.  */
> +	l->l_map_start = l->l_map_end = 0;
> +	goto call_lose;
> +      }
>  
>      /* Process program headers again after load segments are mapped in
>         case processing requires accessing those segments.  Scan program

In this case I am failing to see who would be responsible to unmap 
l_map_start int the type == ET_DYN where first mmap succeeds but
with a later mmap failure in any load command.

> @@ -1294,14 +1305,6 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
>        || (__glibc_unlikely (l->l_flags_1 & DF_1_PIE)
>  	  && __glibc_unlikely ((mode & __RTLD_OPENEXEC) == 0)))
>      {
> -      /* We are not supposed to load this object.  Free all resources.  */
> -      _dl_unmap_segments (l);
> -
> -      if (!l->l_libname->dont_free)
> -	free (l->l_libname);
> -
> -      if (l->l_phdr_allocated)
> -	free ((void *) l->l_phdr);
>  
>        if (l->l_flags_1 & DF_1_PIE)
>  	errstring
> @@ -1392,6 +1395,9 @@ cannot enable executable stack as shared object requires");
>    /* Signal that we closed the file.  */
>    fd = -1;
>  
> +  /* Failures before this point are handled locally via lose.
> +     No more failures are allowed in this function until return.  */
> +
>    /* If this is ET_EXEC, we should have loaded it as lt_executable.  */
>    assert (type != ET_EXEC || l->l_type == lt_executable);
>  
> 

Ok.