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[08/11] uprobes: __replace_page() avoid BUG in munlock_vma_page()

Message ID 20200821004217.UBGpf4I1N%akpm@linux-foundation.org
State New
Headers show
Series + mm-track-page-table-modifications-in-__apply_to_page_range.patch added to -mm tree | expand

Commit Message

Andrew Morton Aug. 21, 2020, 12:42 a.m. UTC 
From: Hugh Dickins <hughd@google.com>
Subject: uprobes: __replace_page() avoid BUG in munlock_vma_page()

syzbot crashed on the VM_BUG_ON_PAGE(PageTail) in munlock_vma_page(), when
called from uprobes __replace_page().  Which of many ways to fix it? 
Settled on not calling when PageCompound (since Head and Tail are equals
in this context, PageCompound the usual check in uprobes.c, and the prior
use of FOLL_SPLIT_PMD will have cleared PageMlocked already).

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008161338360.20413@eggly.anvils
Fixes: 5a52c9df62b4 ("uprobe: use FOLL_SPLIT_PMD instead of FOLL_SPLIT")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: <stable@vger.kernel.org>	[5.4+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/events/uprobes.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
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Patch

--- a/kernel/events/uprobes.c~uprobes-__replace_page-avoid-bug-in-munlock_vma_page
+++ a/kernel/events/uprobes.c
@@ -205,7 +205,7 @@  static int __replace_page(struct vm_area
 		try_to_free_swap(old_page);
 	page_vma_mapped_walk_done(&pvmw);
 
-	if (vma->vm_flags & VM_LOCKED)
+	if ((vma->vm_flags & VM_LOCKED) && !PageCompound(old_page))
 		munlock_vma_page(old_page);
 	put_page(old_page);