Detect ld.so and libc.so version inconsistency during startup

System Internals / glibc - Florian Weimer [redhat.com] - 24 August 2022 15:35 UTC

The files NEWS, include/link.h, and sysdeps/generic/ldsodefs.h contribute to the version fingerprint used for detection. The fingerprint can be further refined using the --with-extra-version-id configure argument.

_dl_call_libc_early_init is replaced with _dl_lookup_libc_early_init. The new function is used store a pointer to libc.so's __libc_early_init function in the libc_map_early_init member of the ld.so namespace structure. This function pointer can then be called directly, so the separate invocation function is no longer needed.

The versioned symbol lookup needs the symbol versioning data structures, so the initialization of libc_map and libc_map_early_init is now done from _dl_check_map_versions, after this information becomes available. (_dl_map_object_from_fd does not set this up in time, so the initialization code had to be moved from there.) This means that the separate initialization code can be removed from dl_main because _dl_check_map_versions covers all maps, including the initial executable loaded by the kernel. The lookup still happens before relocation and the invocation of IFUNC resolvers, so IFUNC resolvers are protected from ABI mismatch.

The __libc_early_init function pointer is not protected because so little code runs between the pointer write and the invocation (only dynamic linker code and IFUNC resolvers).

6f85dbf102 Detect ld.so and libc.so version inconsistency during startup
INSTALL | 10 +++
Makerules | 14 ++++
NEWS | 7 +-
config.make.in | 1 +
configure | 11 +++
configure.ac | 5 ++
elf/Makefile | 2 +-
elf/Versions | 4 +-
elf/dl-load.c | 9 ---
...bc-early-init.c => dl-lookup_libc_early_init.c} | 23 +++---
elf/dl-open.c | 4 +-
elf/dl-version.c | 18 +++++
elf/libc-early-init.h | 21 +++--
elf/rtld.c | 12 +--
manual/install.texi | 9 +++
scripts/libc_early_init_name.py | 89 ++++++++++++++++++++++
sysdeps/generic/ldsodefs.h | 4 +
17 files changed, 198 insertions(+), 45 deletions(-)

Upstream: sourceware.org


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