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ocfs2: fix use-after-free in ocfs2_fault() when VM_FAULT_RETRY

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filemap_fault() may drop the mmap_lock before returning VM_FAULT_RETRY,
as documented in mm/filemap.c:

  "If our return value has VM_FAULT_RETRY set, it's because the mmap_lock
  may be dropped before doing I/O or by lock_folio_maybe_drop_mmap()."

When this happens, a concurrent munmap() can call remove_vma() and free
the vm_area_struct via RCU. The saved 'vma' pointer in ocfs2_fault() then
becomes a dangling pointer, and the subsequent trace_ocfs2_fault() call
dereferences it -- a use-after-free.

Fix this by saving ip_blkno as a plain integer before calling
filemap_fault(), and removing vma from the trace event. Since
ip_blkno is copied by value before the lock can be dropped, it
remains valid regardless of what happens to the vma or inode
afterward.

Link: https://lkml.kernel.org/r/20260410083816.34951-1-tejas.bharambe@outlook.com
Fixes: 614a9e849c ("ocfs2: Remove FILE_IO from masklog.")
Signed-off-by: Tejas Bharambe <tejas.bharambe@outlook.com>
Reported-by: syzbot+a49010a0e8fcdeea075f@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=a49010a0e8fcdeea075f
Suggested-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Cc: Heming Zhao <heming.zhao@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Tejas Bharambe
2026-04-10 01:38:16 -07:00
committed by Andrew Morton
parent 4a1c0ddc6e
commit 7de554cabf
2 changed files with 7 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
fs/ocfs2/mmap.c
View File

@@ -30,7 +30,8 @@
static vm_fault_t ocfs2_fault(struct vm_fault *vmf)
{
struct vm_area_struct *vma = vmf->vma;
unsigned long long ip_blkno =
OCFS2_I(file_inode(vmf->vma->vm_file))->ip_blkno;
sigset_t oldset;
vm_fault_t ret;
@@ -38,11 +39,9 @@ static vm_fault_t ocfs2_fault(struct vm_fault *vmf)
ret = filemap_fault(vmf);
ocfs2_unblock_signals(&oldset);
trace_ocfs2_fault(OCFS2_I(vma->vm_file->f_mapping->host)->ip_blkno,
vma, vmf->page, vmf->pgoff);
trace_ocfs2_fault(ip_blkno, vmf->page, vmf->pgoff);
return ret;
}
static vm_fault_t __ocfs2_page_mkwrite(struct file *file,
struct buffer_head *di_bh, struct folio *folio)
{