From 752015d1b0683a8c623ebfe4c62893413e9b30d3 Mon Sep 17 00:00:00 2001 From: Roland McGrath Date: Tue, 8 Sep 2009 19:49:40 -0700 Subject: [PATCH] binfmt_elf: fix PT_INTERP bss handling In fs/binfmt_elf.c, load_elf_interp() calls padzero() for .bss even if the PT_LOAD has no PROT_WRITE and no .bss. This generates EFAULT. Here is a small test case. (Yes, there are other, useful PT_INTERP which have only .text and no .data/.bss.) ----- ptinterp.S _start: .globl _start nop int3 ----- $ gcc -m32 -nostartfiles -nostdlib -o ptinterp ptinterp.S $ gcc -m32 -Wl,--dynamic-linker=ptinterp -o hello hello.c $ ./hello Segmentation fault # during execve() itself After applying the patch: $ ./hello Trace trap # user-mode execution after execve() finishes If the ELF headers are actually self-inconsistent, then dying is fine. But having no PROT_WRITE segment is perfectly normal and correct if there is no segment with p_memsz > p_filesz (i.e. bss). John Reiser suggested checking for PROT_WRITE in the bss logic. I think it makes most sense to simply apply the bss logic only when there is bss. This patch looks less trivial than it is due to some reindentation. It just moves the "if (last_bss > elf_bss) {" test up to include the partial-page bss logic as well as the more-pages bss logic. Reported-by: John Reiser Signed-off-by: Roland McGrath Signed-off-by: Linus Torvalds --- fs/binfmt_elf.c | 30 +++++++++++++++--------------- 1 file changed, 15 insertions(+), 15 deletions(-) diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index b7c1603cd4b..7c1e65d5487 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -501,22 +501,22 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex, } } - /* - * Now fill out the bss section. First pad the last page up - * to the page boundary, and then perform a mmap to make sure - * that there are zero-mapped pages up to and including the - * last bss page. - */ - if (padzero(elf_bss)) { - error = -EFAULT; - goto out_close; - } - - /* What we have mapped so far */ - elf_bss = ELF_PAGESTART(elf_bss + ELF_MIN_ALIGN - 1); - - /* Map the last of the bss segment */ if (last_bss > elf_bss) { + /* + * Now fill out the bss section. First pad the last page up + * to the page boundary, and then perform a mmap to make sure + * that there are zero-mapped pages up to and including the + * last bss page. + */ + if (padzero(elf_bss)) { + error = -EFAULT; + goto out_close; + } + + /* What we have mapped so far */ + elf_bss = ELF_PAGESTART(elf_bss + ELF_MIN_ALIGN - 1); + + /* Map the last of the bss segment */ down_write(¤t->mm->mmap_sem); error = do_brk(elf_bss, last_bss - elf_bss); up_write(¤t->mm->mmap_sem);