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 <jreiser@bitwagon.com>
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>
1 file changed