From 55c5c9a568ed707bcea1388bf3a525212d8cf4b8 Mon Sep 17 00:00:00 2001 From: Mark Wielaard Date: Wed, 19 Aug 2020 23:41:24 +0200 Subject: [PATCH] libelf: Fixup SHF_COMPRESSED sh_addralign in elf_update if necessary. In elf_getdata.c we have the following to compensate for possibly bad sh_addralign values of compressed sections: /* Compressed data has a header, but then compressed data. Make sure to set the alignment of the header explicitly, don't trust the file alignment for the section, it is often wrong. */ if ((flags & SHF_COMPRESSED) != 0) { entsize = 1; align = __libelf_type_align (elf->class, ELF_T_CHDR); } Which makes sure the d_data alignment is correct for the Chdr struct at the start of the compressed section. But this means that if a user just reads such a compressed section without changing it, and then tries to write it out again using elf_update they get an error message about d_align and sh_addralign being out of sync. We already correct obviously incorrect sh_entsize fields. Do the same for the sh_addralign field of a SHF_COMPRESSED section. Signed-off-by: Mark Wielaard --- libelf/ChangeLog | 5 +++++ libelf/elf32_updatenull.c | 12 ++++++++++++ 2 files changed, 17 insertions(+) diff --git a/libelf/ChangeLog b/libelf/ChangeLog index 8f6d2d2d..77044c1c 100644 --- a/libelf/ChangeLog +++ b/libelf/ChangeLog @@ -1,3 +1,8 @@ +2020-08-19 Mark Wielaard + + * elf32_updatenull.c (updatenull_wrlock): Fixup the sh_addralign + of an SHF_COMPRESSED section if necessary. + 2020-06-04 Mark Wielaard * elf.h: Update from glibc. diff --git a/libelf/elf32_updatenull.c b/libelf/elf32_updatenull.c index 5f3cdbf6..d0d4d1eb 100644 --- a/libelf/elf32_updatenull.c +++ b/libelf/elf32_updatenull.c @@ -267,6 +267,18 @@ __elfw2(LIBELFBITS,updatenull_wrlock) (Elf *elf, int *change_bop, size_t shnum) update_if_changed (shdr->sh_entsize, sh_entsize, scn->shdr_flags); + /* Likewise for the alignment of a compressed section. + For a SHF_COMPRESSED section set the correct + sh_addralign value, which must match the d_align of + the data (see __libelf_set_rawdata in elf_getdata.c). */ + if ((shdr->sh_flags & SHF_COMPRESSED) != 0) + { + sh_align = __libelf_type_align (ELFW(ELFCLASS,LIBELFBITS), + ELF_T_CHDR); + update_if_changed (shdr->sh_addralign, sh_align, + scn->shdr_flags); + } + if (scn->data_read == 0 && __libelf_set_rawdata_wrlock (scn) != 0) /* Something went wrong. The error value is already set. */ -- 2.18.4