Hi David,
On Sun, Apr 20, 2014 at 4:26 AM, Davidlohr Bueso <davidlohr@xxxxxx> wrote:
Performing vma lookups without taking the mm->mmap_sem is asking
for trouble. While doing the search, the vma in question can be
modified or even removed before returning to the caller. Take the
lock (shared) in order to avoid races while iterating through
the vmacache and/or rbtree.
Thanks for your patch!
This patch is completely *untested*.
Signed-off-by: Davidlohr Bueso <davidlohr@xxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Cc: linux-m68k@xxxxxxxxxxxxxxxxxxxx
---
arch/m68k/kernel/sys_m68k.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/arch/m68k/kernel/sys_m68k.c b/arch/m68k/kernel/sys_m68k.c
index 3a480b3..d2263a0 100644
--- a/arch/m68k/kernel/sys_m68k.c
+++ b/arch/m68k/kernel/sys_m68k.c
@@ -376,7 +376,6 @@ cache_flush_060 (unsigned long addr, int scope, int cache, unsigned long len)
asmlinkage int
sys_cacheflush (unsigned long addr, int scope, int cache, unsigned long len)
{
- struct vm_area_struct *vma;
int ret = -EINVAL;
if (scope < FLUSH_SCOPE_LINE || scope > FLUSH_SCOPE_ALL ||
@@ -389,16 +388,23 @@ sys_cacheflush (unsigned long addr, int scope, int cache, unsigned long len)
if (!capable(CAP_SYS_ADMIN))
goto out;
} else {
+ struct vm_area_struct *vma;
+ bool invalid;
+
+ /* Check for overflow. */
+ if (addr + len < addr)
+ goto out;
+
/*
* Verify that the specified address region actually belongs
* to this process.
*/
- vma = find_vma (current->mm, addr);
ret = -EINVAL;
- /* Check for overflow. */
- if (addr + len < addr)
- goto out;
- if (vma == NULL || addr < vma->vm_start || addr + len > vma->vm_end)
+ down_read(¤t->mm->mmap_sem);
+ vma = find_vma(current->mm, addr);
+ invalid = !vma || addr < vma->vm_start || addr + len > vma->vm_end;
+ up_read(¤t->mm->mmap_sem);
+ if (invalid)
goto out;
}
Shouldn't the up_read() be moved to the end of the function?
The vma may still be modified or destroyed between the call to find_vma(),
and the actual cache flush?
Am I missing something?
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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