brk: COMPAT_BRK: fix detection of randomized brk

commit 4471a675dfc7ca676c165079e91c712b09dc9ce4 upstream.

5520e89 ("brk: fix min_brk lower bound computation for COMPAT_BRK")
tried to get the whole logic of brk randomization for legacy
(libc5-based) applications finally right.

It turns out that the way to detect whether brk has actually been
randomized in the end or not introduced by that patch still doesn't work
for those binaries, as reported by Geert:

: /sbin/init from my old m68k ramdisk exists prematurely.
:
: Before the patch:
:
: | brk(0x80005c8e)                         = 0x80006000
:
: After the patch:
:
: | brk(0x80005c8e)                         = 0x80005c8e
:
: Old libc5 considers brk() to have failed if the return value is not
: identical to the requested value.

I don't like it, but currently see no better option than a bit flag in
task_struct to catch the CONFIG_COMPAT_BRK && randomize_va_space == 2
case.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index d5b640ba6cb1a30ab06adc214e76ae37f2b1ec75..70470b2b7f73d213804404929177911b38f1d76c 100644 (file)
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -941,9 +941,13 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
        current->mm->start_stack = bprm->p;
 
 #ifdef arch_randomize_brk
-       if ((current->flags & PF_RANDOMIZE) && (randomize_va_space > 1))
+       if ((current->flags & PF_RANDOMIZE) && (randomize_va_space > 1)) {
                current->mm->brk = current->mm->start_brk =
                        arch_randomize_brk(current->mm);
+#ifdef CONFIG_COMPAT_BRK
+               current->brk_randomized = 1;
+#endif
+       }
 #endif
 
        if (current->personality & MMAP_PAGE_ZERO) {

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 777d8a5ed06beab057a293d33d7a42d9c80ab133..ed6c384ba6c89b21181886daaa7ed6ec3aa028a3 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1254,6 +1254,9 @@ struct task_struct {
 #endif
 
        struct mm_struct *mm, *active_mm;
+#ifdef CONFIG_COMPAT_BRK
+       unsigned brk_randomized:1;
+#endif
 #if defined(SPLIT_RSS_COUNTING)
        struct task_rss_stat    rss_stat;
 #endif

diff --git a/mm/mmap.c b/mm/mmap.c
index 8c05e5b43b69c0f82f218a5f18476e6e7f514aa5..e27e0cf0de03ccb81b252953932fc356c3499c10 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -259,7 +259,7 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
         * randomize_va_space to 2, which will still cause mm->start_brk
         * to be arbitrarily shifted
         */
-       if (mm->start_brk > PAGE_ALIGN(mm->end_data))
+       if (current->brk_randomized)
                min_brk = mm->start_brk;
        else
                min_brk = mm->end_data;