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Fri, 10 Apr 2026 01:38:28 -0700 (PDT) Received: from macbookair ([2600:8802:2a09:a700::2791]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2d562ac344csm3172631eec.25.2026.04.10.01.38.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Apr 2026 01:38:27 -0700 (PDT) From: Tejas Bharambe X-Google-Original-From: Tejas Bharambe To: ocfs2-devel@lists.linux.dev Cc: mark@fasheh.com, jlbec@evilplan.org, joseph.qi@linux.alibaba.com, linux-kernel@vger.kernel.org, syzbot+a49010a0e8fcdeea075f@syzkaller.appspotmail.com, akpm@linux-foundation.org, Tejas Bharambe Subject: [PATCH v6] ocfs2: fix use-after-free in ocfs2_fault() when VM_FAULT_RETRY Date: Fri, 10 Apr 2026 01:38:16 -0700 Message-ID: <20260410083816.34951-1-tejas.bharambe@outlook.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Tejas Bharambe 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. Reported-by: syzbot+a49010a0e8fcdeea075f@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3Da49010a0e8fcdeea075f Suggested-by: Joseph Qi Signed-off-by: Tejas Bharambe Reviewed-by: Joseph Qi --- fs/ocfs2/mmap.c | 7 +++---- fs/ocfs2/ocfs2_trace.h | 10 ++++------ 2 files changed, 7 insertions(+), 10 deletions(-) diff --git a/fs/ocfs2/mmap.c b/fs/ocfs2/mmap.c index 50e2faf64c..6c570157ca 100644 --- a/fs/ocfs2/mmap.c +++ b/fs/ocfs2/mmap.c @@ -30,7 +30,8 @@ =20 static vm_fault_t ocfs2_fault(struct vm_fault *vmf) { - struct vm_area_struct *vma =3D vmf->vma; + unsigned long long ip_blkno =3D + OCFS2_I(file_inode(vmf->vma->vm_file))->ip_blkno; sigset_t oldset; vm_fault_t ret; =20 @@ -38,11 +39,9 @@ static vm_fault_t ocfs2_fault(struct vm_fault *vmf) ret =3D filemap_fault(vmf); ocfs2_unblock_signals(&oldset); =20 - 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) { diff --git a/fs/ocfs2/ocfs2_trace.h b/fs/ocfs2/ocfs2_trace.h index 4b32fb5658..6c2c97a980 100644 --- a/fs/ocfs2/ocfs2_trace.h +++ b/fs/ocfs2/ocfs2_trace.h @@ -1246,22 +1246,20 @@ TRACE_EVENT(ocfs2_write_end_inline, =20 TRACE_EVENT(ocfs2_fault, TP_PROTO(unsigned long long ino, - void *area, void *page, unsigned long pgoff), - TP_ARGS(ino, area, page, pgoff), + void *page, unsigned long pgoff), + TP_ARGS(ino, page, pgoff), TP_STRUCT__entry( __field(unsigned long long, ino) - __field(void *, area) __field(void *, page) __field(unsigned long, pgoff) ), TP_fast_assign( __entry->ino =3D ino; - __entry->area =3D area; __entry->page =3D page; __entry->pgoff =3D pgoff; ), - TP_printk("%llu %p %p %lu", - __entry->ino, __entry->area, __entry->page, __entry->pgoff) + TP_printk("%llu %p %lu", + __entry->ino, __entry->page, __entry->pgoff) ); =20 /* End of trace events for fs/ocfs2/mmap.c. */ --=20 2.53.0