From 4eb919825e6c3c7fb3630d5621f6d11e98a18b3a Mon Sep 17 00:00:00 2001 From: Rik van Riel Date: Thu, 2 Jan 2014 12:58:46 -0800 Subject: [PATCH] mm: fix use-after-free in sys_remap_file_pages remap_file_pages calls mmap_region, which may merge the VMA with other existing VMAs, and free "vma". This can lead to a use-after-free bug. Avoid the bug by remembering vm_flags before calling mmap_region, and not trying to dereference vma later. Signed-off-by: Rik van Riel Reported-by: Dmitry Vyukov Cc: PaX Team Cc: Kees Cook Cc: Michel Lespinasse Cc: Cyrill Gorcunov Cc: Hugh Dickins Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/fremap.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/mm/fremap.c b/mm/fremap.c index 5bff08147768..bbc4d660221a 100644 --- a/mm/fremap.c +++ b/mm/fremap.c @@ -208,9 +208,10 @@ get_write_lock: if (mapping_cap_account_dirty(mapping)) { unsigned long addr; struct file *file = get_file(vma->vm_file); + /* mmap_region may free vma; grab the info now */ + vm_flags = vma->vm_flags; - addr = mmap_region(file, start, size, - vma->vm_flags, pgoff); + addr = mmap_region(file, start, size, vm_flags, pgoff); fput(file); if (IS_ERR_VALUE(addr)) { err = addr; @@ -218,7 +219,7 @@ get_write_lock: BUG_ON(addr != start); err = 0; } - goto out; + goto out_freed; } mutex_lock(&mapping->i_mmap_mutex); flush_dcache_mmap_lock(mapping); @@ -253,6 +254,7 @@ get_write_lock: out: if (vma) vm_flags = vma->vm_flags; +out_freed: if (likely(!has_write_lock)) up_read(&mm->mmap_sem); else -- 2.34.1