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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm/kernel/swp_emulate.c b/arch/arm/kernel/swp_emulate.c
index 40ee7e5045e40f7a1f78cd8bd9d632b9130175b3..0951a32493ae82fb84a5502c78dc89a0abe7bb14 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;