From 2b39baf48e7fbbb806bbab08acdad3b10ef26b2f Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Thu, 20 Aug 2020 17:42:17 -0700 Subject: [PATCH] uprobes: __replace_page() avoid BUG in munlock_vma_page() BugLink: https://bugs.launchpad.net/bugs/1893115 commit c17c3dc9d08b9aad9a55a1e53f205187972f448e upstream. 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). Fixes: 5a52c9df62b4 ("uprobe: use FOLL_SPLIT_PMD instead of FOLL_SPLIT") Reported-by: syzbot Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Reviewed-by: Srikar Dronamraju Acked-by: Song Liu Acked-by: Oleg Nesterov Cc: "Kirill A. Shutemov" Cc: [5.4+] Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008161338360.20413@eggly.anvils Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman Signed-off-by: Kamal Mostafa Signed-off-by: Khalid Elmously --- kernel/events/uprobes.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index aa83538efc23..a793bd23fe56 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -211,7 +211,7 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr, 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); -- 2.39.5