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checkout: Ensure copies of unreadable usermode checkouts are readable

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The extreme special case of "zero mode" files like `/etc/shadow`
comes up again.  What we want is for "user mode" checkouts to
override it to make the file readable; otherwise when operating
as non-root without `CAP_DAC_OVERRIDE` it becomes very difficult
to work with.

Previously, we were hardlinking these files, but then it intersects
with *another* special case around zero sized files, which is
*also* true for `/etc/shadow`.

Trying to avoid hardlinking there unveiled this bug - when
we go to do a copy checkout, we need to override the mode.
This commit is contained in:
Colin Walters 2020-09-16 13:23:04 +00:00
parent ca2f3435be
commit 3441a48c58
2 changed files with 18 additions and 4 deletions
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20
src/libostree/ostree-repo-checkout.c
View File

@ -613,9 +613,12 @@ checkout_one_file_at (OstreeRepo *repo,
}
const gboolean is_symlink = (g_file_info_get_file_type (source_info) == G_FILE_TYPE_SYMBOLIC_LINK);
const guint32 source_mode = g_file_info_get_attribute_uint32 (source_info, "unix::mode");
const gboolean is_unreadable = (!is_symlink && (source_mode & S_IRUSR) == 0);
const gboolean is_whiteout = (!is_symlink && options->process_whiteouts &&
g_str_has_prefix (destination_name, WHITEOUT_PREFIX));
const gboolean is_reg_zerosized = (!is_symlink && g_file_info_get_size (source_info) == 0);
const gboolean override_user_unreadable = (options->mode == OSTREE_REPO_CHECKOUT_MODE_USER && is_unreadable);
/* First, see if it's a Docker whiteout,
* https://github.com/docker/docker/blob/1a714e76a2cb9008cd19609059e9988ff1660b78/pkg/archive/whiteouts.go
@ -634,7 +637,7 @@ checkout_one_file_at (OstreeRepo *repo,
need_copy = FALSE;
}
else if (options->force_copy_zerosized && is_reg_zerosized)
else if ((options->force_copy_zerosized && is_reg_zerosized) || override_user_unreadable)
{
need_copy = TRUE;
}
@ -735,7 +738,7 @@ checkout_one_file_at (OstreeRepo *repo,
if (can_cache
&& !is_whiteout
&& !is_symlink
&& !is_reg_zerosized
&& !(is_reg_zerosized || override_user_unreadable)
&& need_copy
&& repo->mode == OSTREE_REPO_MODE_ARCHIVE
&& options->mode == OSTREE_REPO_CHECKOUT_MODE_USER)
@ -799,12 +802,21 @@ checkout_one_file_at (OstreeRepo *repo,
* succeeded at hardlinking above.
*/
if (options->no_copy_fallback)
g_assert (is_bare_user_symlink || is_reg_zerosized);
g_assert (is_bare_user_symlink || is_reg_zerosized || override_user_unreadable);
if (!ostree_repo_load_file (repo, checksum, &input, NULL, &xattrs,
cancellable, error))
return FALSE;
if (!create_file_copy_from_input_at (repo, options, state, checksum, source_info, xattrs, input,
GFileInfo *copy_source_info = source_info;
g_autoptr(GFileInfo) modified_info = NULL;
if (override_user_unreadable)
{
modified_info = g_file_info_dup (source_info);
g_file_info_set_attribute_uint32 (modified_info, "unix::mode", (source_mode | S_IRUSR));
copy_source_info = modified_info;
}
if (!create_file_copy_from_input_at (repo, options, state, checksum, copy_source_info, xattrs, input,
destination_dfd, destination_name,
cancellable, error))
return glnx_prefix_error (error, "Copy checkout of %s to %s", checksum, destination_name);

2
tests/test-basic-user.sh
View File

@ -75,6 +75,8 @@ $OSTREE fsck
rm test2-checkout -rf
$OSTREE checkout -U -H test2-unreadable test2-checkout
assert_file_has_mode test2-checkout/unreadable 400
# Should not be hardlinked
assert_streq $(stat -c "%h" test2-checkout/unreadable) 1
echo "ok bare-user handled unreadable file"
cd ${test_tmpdir}