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elf-util: discard PT_LOAD segment early based on the start address.

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Indeed when iterating over all the PT_LOAD segment of the core dump
while trying to look for the elf headers of a given module, we iterate
over them all and try to use the first one for which we can parse a
package metadata, but the start address is never taken into account,
so absolutely nothing guarantees we actually parse the right ELF header
of the right module we are currently iterating on.

This was tested like this:
 - Create a core dump using sleep on a fedora 37 container, with an
   explicit LD_PRELOAD of a library having a valid package metadata:

    podman run -t -i --rm -v $(pwd):$(pwd) -w $(pwd) fedora:37 bash -x -c \
        'LD_PRELOAD=libreadline.so.8 sleep 1000 & SLEEP_PID="$!" && sleep 1 && kill -11 "${SLEEP_PID}" && mv "core.${SLEEP_PID}" the-core'

 - Then from a fedora 38 container with systemd installed, the resulting
   core dump has been passed to systemd-coredump with and without this
   patch. Without this patch, we get:

       Module /usr/bin/sleep from rpm bash-5.2.15-3.fc38.x86_64
       Module /usr/lib64/libtinfo.so.6.3 from rpm coreutils-9.1-8.fc37.x86_64
       Module /usr/lib64/libc.so.6 from rpm coreutils-9.1-8.fc37.x86_64
       Module /usr/lib64/libreadline.so.8.2 from rpm coreutils-9.1-8.fc37.x86_64
       Module /usr/lib64/ld-linux-x86-64.so.2 from rpm coreutils-9.1-8.fc37.x86_64

   While with this patch we get:

       Module /usr/bin/sleep from rpm bash-5.2.15-3.fc38.x86_64
       Module /usr/lib64/libtinfo.so.6.3 from rpm ncurses-6.3-5.20220501.fc37.x86_64
       Module /usr/lib64/libreadline.so.8.2 from rpm readline-8.2-2.fc37.x86_64

So the parsed package metadata reported by systemd-coredump when the module
files are not found on the host (ie the case of crash inside a container) are
now correct. The inconsistency of the first module in the above example
(sleep is indeed not provided by the bash package) can be ignored as it
is a consequence of how this was tested.

In addition to this, this also fixes the performance issue of
systemd-coredump in case of the crashing process uses a large number of
shared libraries and having no package metadata, as reported in
https://sourceware.org/pipermail/elfutils-devel/2023q2/006225.html.
This commit is contained in:
Romain Geissler 2023-06-20 16:06:31 +00:00 committed by Luca Boccassi
parent 33885343cf
commit 21a2c735e2
1 changed files with 4 additions and 0 deletions
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4
src/shared/elf-util.c
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@ -538,6 +538,10 @@ static int module_callback(Dwfl_Module *mod, void **userdata, const char *name,
if (!program_header || program_header->p_type != PT_LOAD)
continue;
/* This PT_LOAD segment doesn't contain the start address, so it can't be the module we are looking for. */
if (start < program_header->p_vaddr || start >= program_header->p_vaddr + program_header->p_memsz)
continue;
/* Now get a usable Elf reference, and parse the notes from it. */
data = sym_elf_getdata_rawchunk(elf,
program_header->p_offset,