Compressing a section that is already compressed is fine, but useless. But it isn't possible to gnu compress (or decompress) a SHF_COMPRESSED section since there is no state kept that would tell if the section was first GNU compressed or first gabi compressed. Calling elf_compress_gnu on a section and then calling elf_compress on it to decompress it twice could cause a crash (the other way around is fine). Just disallow it.
https://sourceware.org/bugzilla/show_bug.cgi?id=23528 Signed-off-by: Mark Wielaard <m...@klomp.org> --- libelf/ChangeLog | 7 +++++++ libelf/elf_compress_gnu.c | 4 +++- libelf/libelf.h | 5 +++++ 3 files changed, 15 insertions(+), 1 deletion(-) diff --git a/libelf/ChangeLog b/libelf/ChangeLog index 744c5b4d..7c884b00 100644 --- a/libelf/ChangeLog +++ b/libelf/ChangeLog @@ -1,3 +1,10 @@ +2018-08-18 Mark Wielaard <m...@klomp.org> + + * libelf.h (elf_compress_gnu): Add documentation about + interaction between SHF_COMPRESED and elf_compress_gnu. + * elf_compress_gnu.c (elf_compress_gnu): Return error if section + sh_flags has SHF_COMPRESSED set. + 2018-07-27 Mark Wielaard <m...@klomp.org> * libelf.h (elf_getshdrstrndx): Fix documentation. diff --git a/libelf/elf_compress_gnu.c b/libelf/elf_compress_gnu.c index c35dc395..dfa7c571 100644 --- a/libelf/elf_compress_gnu.c +++ b/libelf/elf_compress_gnu.c @@ -80,7 +80,9 @@ elf_compress_gnu (Elf_Scn *scn, int inflate, unsigned int flags) sh_addralign = shdr->sh_addralign; } - if ((sh_flags & SHF_ALLOC) != 0) + /* Allocated sections, or sections that are already are compressed + cannot (also) be GNU compressed. */ + if ((sh_flags & SHF_ALLOC) != 0 || (sh_flags & SHF_COMPRESSED)) { __libelf_seterrno (ELF_E_INVALID_SECTION_FLAGS); return -1; diff --git a/libelf/libelf.h b/libelf/libelf.h index 61f19231..d11358cc 100644 --- a/libelf/libelf.h +++ b/libelf/libelf.h @@ -366,6 +366,11 @@ extern Elf64_Chdr *elf64_getchdr (Elf_Scn *__scn); It is an error to request compression for a section that already has SHF_COMPRESSED set, or (for elf_compress) to request decompression for an section that doesn't have SHF_COMPRESSED set. + If a section has SHF_COMPRESSED set then calling elf_compress_gnu + will result in an error. The section has to be decompressed first + using elf_compress. Calling elf_compress on a section compressed + with elf_compress_gnu is fine, but probably useless. + It is always an error to call these functions on SHT_NOBITS sections or if the section has the SHF_ALLOC flag set. elf_compress_gnu will not check whether the section name starts -- 2.18.0
