提交 752015d1 编写于 作者: R Roland McGrath 提交者: Linus Torvalds

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: NJohn Reiser <jreiser@bitwagon.com>
Signed-off-by: NRoland McGrath <roland@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
上级 74fca6a4
...@@ -501,22 +501,22 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex, ...@@ -501,22 +501,22 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
} }
} }
/* 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 * Now fill out the bss section. First pad the last page up
* that there are zero-mapped pages up to and including the * to the page boundary, and then perform a mmap to make sure
* last bss page. * that there are zero-mapped pages up to and including the
*/ * last bss page.
if (padzero(elf_bss)) { */
error = -EFAULT; if (padzero(elf_bss)) {
goto out_close; error = -EFAULT;
} goto out_close;
}
/* What we have mapped so far */ /* What we have mapped so far */
elf_bss = ELF_PAGESTART(elf_bss + ELF_MIN_ALIGN - 1); elf_bss = ELF_PAGESTART(elf_bss + ELF_MIN_ALIGN - 1);
/* Map the last of the bss segment */ /* Map the last of the bss segment */
if (last_bss > elf_bss) {
down_write(&current->mm->mmap_sem); down_write(&current->mm->mmap_sem);
error = do_brk(elf_bss, last_bss - elf_bss); error = do_brk(elf_bss, last_bss - elf_bss);
up_write(&current->mm->mmap_sem); up_write(&current->mm->mmap_sem);
......
Markdown is supported
0% .
You are about to add 0 people to the discussion. Proceed with caution.
先完成此消息的编辑!
想要评论请 注册