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authorRoland McGrath <roland@redhat.com>2009-09-08 19:49:40 -0700
committerGreg Kroah-Hartman <gregkh@suse.de>2009-09-24 08:43:51 -0700
commit4e499625e94ea62f93d91832e5a804555b0ea222 (patch)
tree7a09f784e620ff3cb07551be61f849ed2e708cd6
parent3cfbbe0e83024a77c9626977f1d59224b9f92860 (diff)
downloadlinux-linaro-stable-4e499625e94ea62f93d91832e5a804555b0ea222.tar.gz
binfmt_elf: fix PT_INTERP bss handling
commit 9f0ab4a3f0fdb1ff404d150618ace2fa069bb2e1 upstream. 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> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--fs/binfmt_elf.c28
1 files changed, 14 insertions, 14 deletions
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index b7c1603cd4bd..7c1e65d54872 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;
- }
+ 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);
+ /* 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) {
+ /* Map the last of the bss segment */
down_write(&current->mm->mmap_sem);
error = do_brk(elf_bss, last_bss - elf_bss);
up_write(&current->mm->mmap_sem);