ARM: missing ->mmap_sem around find_vma() in swp_emulate.c

commit 7bf9b7bef881aac820bf1f2e9951a17b09bd7e04 upstream.

find_vma() is *not* safe when somebody else is removing vmas.  Not just
the return value might get bogus just as you are getting it (this instance
doesn't try to dereference the resulting vma), the search itself can get
buggered in rather spectacular ways.  IOW, ->mmap_sem really, really is
not optional here.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/arm/kernel/swp_emulate.c b/arch/arm/kernel/swp_emulate.c
index 5f452f8fde0569d140e0d6055220f29be08396f1..5d9b1eeecfd14e89e628b3e7aa826a4b113ea058 100644 (file)
--- a/arch/arm/kernel/swp_emulate.c
+++ b/arch/arm/kernel/swp_emulate.c
@@ -108,10 +108,12 @@ static void set_segfault(struct pt_regs *regs, unsigned long addr)
 {
        siginfo_t info;
 
+       down_read(&current->mm->mmap_sem);
        if (find_vma(current->mm, addr) == NULL)
                info.si_code = SEGV_MAPERR;
        else
                info.si_code = SEGV_ACCERR;
+       up_read(&current->mm->mmap_sem);
 
        info.si_signo = SIGSEGV;
        info.si_errno = 0;