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Rajesh Venkatasubramanian <vrajesh@umich.edu> wrote: > > This path fixes a NULL pointer dereference bug in mremap. In > move_one_page we need to re-check the src because an allocation > for the dst page table can drop page_table_lock, and somebody > else can invalidate the src. OK. > In my old Quad Pentium II 200MHz 256MB, with 2.6.3-rc3-mm1-preempt, > I could hit the NULL pointer dereference bug with the program in the > following URL: > > http://www-personal.engin.umich.edu/~vrajesh/linux/mremap-nullptr/ I cannot make any oops happen with that test app. On a 2-way, CONFIG_PREEMPT=y. I think we can simplify things in there a bit. How does this look? mm/mremap.c | 16 +++++++++------- 1 files changed, 9 insertions(+), 7 deletions(-) diff -puN mm/mremap.c~mremap-oops-fix mm/mremap.c --- 25/mm/mremap.c~mremap-oops-fix 2004-02-16 20:53:25.000000000 -0800 +++ 25-akpm/mm/mremap.c 2004-02-16 21:00:05.000000000 -0800 @@ -135,15 +135,17 @@ move_one_page(struct vm_area_struct *vma dst = alloc_one_pte_map(mm, new_addr); if (src == NULL) src = get_one_pte_map_nested(mm, old_addr); - error = copy_one_pte(vma, old_addr, src, dst, &pte_chain); - pte_unmap_nested(src); - pte_unmap(dst); - } else /* - * Why do we need this flush ? If there is no pte for - * old_addr, then there must not be a pte for it as well. + * Since alloc_one_pte_map can drop and re-acquire + * page_table_lock, we should re-check the src entry... */ - flush_tlb_page(vma, old_addr); + if (src) { + error = copy_one_pte(vma, old_addr, src, + dst, &pte_chain); + pte_unmap_nested(src); + } + pte_unmap(dst); + } spin_unlock(&mm->page_table_lock); pte_chain_free(pte_chain); out: _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | |||||||||
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