Commit 752015d1 authored by Roland McGrath's avatar Roland McGrath Committed by Linus Torvalds
Browse files

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
	$ 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: default avatarJohn Reiser <>
Signed-off-by: default avatarRoland McGrath <>
Signed-off-by: default avatarLinus Torvalds <>
parent 74fca6a4
......@@ -501,6 +501,7 @@ 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
......@@ -516,7 +517,6 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
elf_bss = ELF_PAGESTART(elf_bss + ELF_MIN_ALIGN - 1);
/* Map the last of the bss segment */
if (last_bss > elf_bss) {
error = do_brk(elf_bss, last_bss - elf_bss);
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