[Bug debuginfod/28240] New: debuginfod client cache falsely sticky for root user
fche at redhat dot com
Tue Aug 17 10:25:13 GMT 2021
Bug ID: 28240
Summary: debuginfod client cache falsely sticky for root user
Assignee: unassigned at sourceware dot org
Reporter: fche at redhat dot com
CC: elfutils-devel at sourceware dot org
Target Milestone: ---
bug #25628 introduced a negative-hit caching facility in the debuginfod client,
which represents upstream misses with short-lived permission-000 files in the
cache. These files are used to shortcut repeated queries that are expected to
fail, for a limited time.
The logic works for normal users, but breaks for root users. The problem is
that the way the client recognizes a 000 negative-hit file in the cache, vs. a
good file, is by looking for -EACCES upon opening the file. Unfortunately,
root users never get -EACCES, even for perm-000 files. So a 000 file for root
is treated as though it was a successful fetch of a 0-length file, and poisons
the cache indefinitely.
745 struct stat st;
746 time_t cache_miss;
747 /* Check if the file exists and it's of permission 000*/
748 if (errno == EACCES
749 && stat(target_cache_path, &st) == 0
750 && (st.st_mode & 0777) == 0)
Probably the simplest fix is to ditch the "errno == EACCESS" part of the test,
and perform the stat every time.
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