Traditionally, only the final PT_LOAD for load_elf_interp() supported having p_memsz > p_filesz. Recently, lld's construction of musl's libc.so on PowerPC64 started having two PT_LOAD program headers with p_memsz > p_filesz. As the least invasive change possible, check for p_memsz > p_filesz for each PT_LOAD in load_elf_interp. Reported-by: Rich Felker <dalias@xxxxxxxx> Link: https://maskray.me/blog/2022-11-05-lld-musl-powerpc64 Cc: Pedro Falcato <pedro.falcato@xxxxxxxxx> Cc: Fangrui Song <maskray@xxxxxxxxxx> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx> Cc: linux-fsdevel@xxxxxxxxxxxxxxx Cc: linux-mm@xxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- v2: I realized we need to retain the final padding call. v1: https://lore.kernel.org/linux-hardening/20221111055747.never.202-kees@xxxxxxxxxx/ --- fs/binfmt_elf.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index 528e2ac8931f..0a24bbbef1d6 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -673,15 +673,25 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex, last_bss = k; bss_prot = elf_prot; } + + /* + * Clear any p_memsz > p_filesz area up to the end + * of the page to wipe anything left over from the + * loaded file contents. + */ + if (last_bss > elf_bss && padzero(elf_bss)) + error = -EFAULT; + goto out; + } } } /* - * Now fill out the bss section: first pad the last page from - * the file up to the page boundary, and zero it from elf_bss - * up to the end of the page. + * Finally, pad the last page from the file up to the page boundary, + * and zero it from elf_bss up to the end of the page, if this did + * not already happen with the last PT_LOAD. */ - if (padzero(elf_bss)) { + if (last_bss == elf_bss && padzero(elf_bss)) { error = -EFAULT; goto out; } -- 2.34.1
