Messages in this thread Patch in this message | | | From | David Howells <> | Subject | [PATCH 5/6] NOMMU: Fix race between ramfs truncation and shared mmap | Date | Fri, 08 Jan 2010 22:05:38 +0000 |
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Fix the race between the truncation of a ramfs file and an attempt to make a shared mmap of region of that file.
The problem is that do_mmap_pgoff() calls f_op->get_unmapped_area() to verify that the file region is made of contiguous pages and to find its base address - but there isn't any locking to guarantee this region until vma_prio_tree_insert() is called by add_vma_to_mm().
Note that moving the functionality into f_op->mmap() doesn't help as that is also called before vma_prio_tree_insert().
Instead make ramfs_nommu_check_mappings() grab nommu_region_sem whilst it does its checks. This means that this function will wait whilst mmaps take place.
Signed-off-by: David Howells <dhowells@redhat.com> ---
fs/ramfs/file-nommu.c | 7 ++++++- include/linux/sched.h | 2 +- 2 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c index 2efc571..2665313 100644 --- a/fs/ramfs/file-nommu.c +++ b/fs/ramfs/file-nommu.c @@ -131,6 +131,8 @@ static int ramfs_nommu_check_mappings(struct inode *inode, struct vm_area_struct *vma; struct prio_tree_iter iter; + down_write(&nommu_region_sem); + /* search for VMAs that fall within the dead zone */ vma_prio_tree_foreach(vma, &iter, &inode->i_mapping->i_mmap, newsize >> PAGE_SHIFT, @@ -138,10 +140,13 @@ static int ramfs_nommu_check_mappings(struct inode *inode, ) { /* found one - only interested if it's shared out of the page * cache */ - if (vma->vm_flags & VM_SHARED) + if (vma->vm_flags & VM_SHARED) { + up_write(&nommu_region_sem); return -ETXTBSY; /* not quite true, but near enough */ + } } + up_write(&nommu_region_sem); return 0; } diff --git a/include/linux/sched.h b/include/linux/sched.h index 08a2523..6f7bba9 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -389,7 +389,7 @@ arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr, extern void arch_unmap_area(struct mm_struct *, unsigned long); extern void arch_unmap_area_topdown(struct mm_struct *, unsigned long); #else -extern void arch_pick_mmap_layout(struct mm_struct *mm) {} +static inline void arch_pick_mmap_layout(struct mm_struct *mm) {} #endif #if USE_SPLIT_PTLOCKS
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