build initramfs: uncontrolled LD_LIBRARY_PATH

build initramfs: uncontrolled LD_LIBRARY_PATH

[John Reiser]

dracut uses ldd when building an initramfs, but I cannot find where
dracut controls LD_LIBRARY_PATH during the build.  Thus I do not trust
the results of ldd.  The string "LD_LIBRARY_PATH" does not appear
in the dracut source tree, there is no use of "env -i", dracut is
not setuid, etc.

At a minimum, the built initramfs could fail to satisfy some DT_NEEDED
entry during boot, leading to a crash.  Some soname was satisfied by
a library in a non-standard directory on the build-time LD_LIBRARY_PATH,
and was copied into that non-standard directory of the initramfs, but is
not findable using the boot-time (default standard) path list.

That might be the worst, because all users of the initramfs (namely:
booting only) do control LD_LIBRARY_PATH, so there might be "no possibility"
of substituting an actual non-standard library.  However, it would be
safer to control LD_LIBRARY_PATH while building initramfs, or at least
document why not.

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Re: build initramfs: uncontrolled LD_LIBRARY_PATH

[Harald Hoyer]

On 19.08.2011 05:48, John Reiser wrote:
> dracut uses ldd when building an initramfs, but I cannot find where
> dracut controls LD_LIBRARY_PATH during the build.  Thus I do not trust
> the results of ldd.  The string "LD_LIBRARY_PATH" does not appear
> in the dracut source tree, there is no use of "env -i", dracut is
> not setuid, etc.
> 
> At a minimum, the built initramfs could fail to satisfy some DT_NEEDED
> entry during boot, leading to a crash.  Some soname was satisfied by
> a library in a non-standard directory on the build-time LD_LIBRARY_PATH,
> and was copied into that non-standard directory of the initramfs, but is
> not findable using the boot-time (default standard) path list.
> 
> That might be the worst, because all users of the initramfs (namely:
> booting only) do control LD_LIBRARY_PATH, so there might be "no possibility"
> of substituting an actual non-standard library.  However, it would be
> safer to control LD_LIBRARY_PATH while building initramfs, or at least
> document why not.
> 

good find!

diff --git a/dracut b/dracut
index cf27b23..dfa71a1 100755
--- a/dracut
+++ b/dracut
@@ -265,6 +265,7 @@ fi

 PATH=/sbin:/bin:/usr/sbin:/usr/bin
 export PATH
+unset LD_LIBRARY_PATH

 [[ $debug ]] && {
     export PS4='${BASH_SOURCE}@${LINENO}(${FUNCNAME[0]}): ';

Re: build initramfs: uncontrolled LD_LIBRARY_PATH

[John Reiser]

> --- a/dracut
> +++ b/dracut
> @@ -265,6 +265,7 @@ fi
> 
>  PATH=/sbin:/bin:/usr/sbin:/usr/bin
>  export PATH
> +unset LD_LIBRARY_PATH

Also unset LD_PRELOAD, although it's not quite as bad as LD_LIBRARY_PATH.
[See "LD_PRELOAD=/lib64/libreadline.so.6 ldd /bin/date".]

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