patch resend updated: PR28240, debuginfod cache for root

  commit 56f40abf2cf18775deb25797e1b89e7788b80630 (HEAD -> master)
Author: Frank Ch. Eigler <fche@redhat.com>
Date:   Wed Aug 18 18:29:34 2021 -0400

    PR28240: debuginfod client root-safe negative caching
    
    Negative cache (000-permission) files were incorrectly treated as
    valid cached files for the root user, because root can open even
    000-perm files without -EACCES.  Corrected this checking sequence.
    
    Fixed the debuginfod testsuite to run to completion as root or
    as an ordinary user, correcting corresponding permission checks:
        stat -c %A $FILE
    is right and
        [ -w $FILE]  [ -r $FILE ]
    were wrong.
    
    Signed-off-by: Frank Ch. Eigler <fche@redhat.com>
  

Hi Frank,

On Thu, 2021-09-30 at 14:36 -0400, Frank Ch. Eigler via Elfutils-devel
wrote:
> @@ -766,24 +766,14 @@ debuginfod_query_server (debuginfod_client *c,
>    if (rc != 0)
>      goto out;
>  
> -  /* If the target is already in the cache then we are done.  */
> -  int fd = open (target_cache_path, O_RDONLY);
> -  if (fd >= 0)
> -    {
> -      /* Success!!!! */
> -      if (path != NULL)
> -        *path = strdup(target_cache_path);
> -      rc = fd;
> -      goto out;
> -    }
> -
>    struct stat st;
> -  time_t cache_miss;
> -  /* Check if the file exists and it's of permission 000*/
> -  if (errno == EACCES
> -      && stat(target_cache_path, &st) == 0
> +  /* Check if the file exists and it's of permission 000; must check
> +     explicitly rather than trying to open it first (PR28240). */
> +  if (stat(target_cache_path, &st) == 0
>        && (st.st_mode & 0777) == 0)
>      {
> +      time_t cache_miss;
> +
>        rc = debuginfod_config_cache(cache_miss_path,
> cache_miss_default_s, &st);
>        if (rc < 0)
>          goto out;
> @@ -797,6 +787,18 @@ debuginfod_query_server (debuginfod_client *c,
>        else
>          unlink(target_cache_path);
>      }
> +  
> +  /* If the target is already in the cache, and not a 000 file
> (PR28240), 
> +     then we are done. */
> +  int fd = open (target_cache_path, O_RDONLY);
> +  if (fd >= 0)
> +    {
> +      /* Success!!!! */
> +      if (path != NULL)
> +        *path = strdup(target_cache_path);
> +      rc = fd;
> +      goto out;
> +    }

Isn't this a time-of-check to time-of-use (TOCTOU) race now?
At least for the root user?
 
>    long timeout = default_timeout;
>    const char* timeout_envvar = getenv(DEBUGINFOD_TIMEOUT_ENV_VAR);
> diff --git a/tests/ChangeLog b/tests/ChangeLog
> index 578e8cb15502..e5aca513f1e8 100644
> --- a/tests/ChangeLog
> +++ b/tests/ChangeLog
> @@ -1,3 +1,9 @@
> +2021-09-30  Frank Ch. Eigler  <fche@redhat.com>
> +
> +	PR28240
> +	* run-debuginfod-000-permission.sh, -writable.sh:
> +	Correct negative-cache file permission checking.
> +
>  2021-09-30  Frank Ch. Eigler  <fche@redhat.com>
>  
>  	* run-debuginfod-*.sh: Use ! CMD to assert expected failure.
> diff --git a/tests/run-debuginfod-000-permission.sh b/tests/run-
> debuginfod-000-permission.sh
> index 8480ad486886..301ce7e7d9d3 100755
> --- a/tests/run-debuginfod-000-permission.sh
> +++ b/tests/run-debuginfod-000-permission.sh
> @@ -56,7 +56,7 @@ if [ ! -f $DEBUGINFOD_CACHE_PATH/01234567/debuginfo
> ]; then
>    err
>  fi
>  
> -if [ -r $DEBUGINFOD_CACHE_PATH/01234567/debuginfo ]; then
> +if [ `stat -c "%A" $DEBUGINFOD_CACHE_PATH/01234567/debuginfo` != "
> ----------" ]; then
>    echo "The cache $DEBUGINFOD_CACHE_PATH/01234567/debuginfo is
> readable"
>    err
>  fi
> diff --git a/tests/run-debuginfod-artifact-running.sh b/tests/run-
> debuginfod-artifact-running.sh
> index 51fa9c0a40bd..b94444267ade 100755
> --- a/tests/run-debuginfod-artifact-running.sh
> +++ b/tests/run-debuginfod-artifact-running.sh
> @@ -90,10 +90,6 @@ wait_ready $PORT1 'thread_busy{role="scan"}' 0
>  rm -rf $DEBUGINFOD_CACHE_PATH # clean it from previous tests
>  filename=`testrun ${abs_top_builddir}/debuginfod/debuginfod-find
> debuginfo $BUILDID`
>  cmp $filename F/prog.debug
> -if [ -w $filename ]; then
> -    echo "cache file writable, boo"
> -    err
> -fi

I assume you are just removing the test here, instead of replacing,
because it is already tested in the next one?

>  filename=`testrun ${abs_top_builddir}/debuginfod/debuginfod-find
> executable F/prog`
>  cmp $filename F/prog
> diff --git a/tests/run-debuginfod-writable.sh b/tests/run-debuginfod-
> writable.sh
> index 69ececb39454..9cc4ea1db92c 100755
> --- a/tests/run-debuginfod-writable.sh
> +++ b/tests/run-debuginfod-writable.sh
> @@ -79,7 +79,7 @@ wait_ready $PORT1 'thread_busy{role="scan"}' 0
>  rm -rf $DEBUGINFOD_CACHE_PATH # clean it from previous tests
>  filename=`testrun ${abs_top_builddir}/debuginfod/debuginfod-find
> debuginfo $BUILDID`
>  cmp $filename F/p+r%o\$g.debug
> -if [ -w $filename ]; then
> +if [  `stat -c "%A" $filename` != "-r--------" ]; then
>      echo "cache file writable, boo"
>      err
>  fi

Cheers,

Mark