linux-kernel - Bug in find_vma_prev

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Message-ID: <6cafb0f01001291657q4ccbee86rce3143a4be7a1433@mail.gmail.com>
Date:	Fri, 29 Jan 2010 16:57:31 -0800
From:	Tony Perkins <da.perk@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Bug in find_vma_prev - mmap.c

This code returns vma (mm->mmap) if it sees that addr is lower than first VMA.
However, I think it falsely returns vma (mm->mmap) on the case where
addr is in the first VMA.

If it is the first VMA region:
- *pprev should be set to NULL
- implying prev is NULL
- and should therefore return vma (so in this case, I just added if
it's the first VMA and it's within range)

/* Same as find_vma, but also return a pointer to the previous VMA in *pprev. */
struct vm_area_struct *
find_vma_prev(struct mm_struct *mm, unsigned long addr,
            struct vm_area_struct **pprev)
{
    struct vm_area_struct *vma = NULL, *prev = NULL;
    struct rb_node *rb_node;
    if (!mm)
        goto out;

    /* Guard against addr being lower than the first VMA */
    vma = mm->mmap;

    /* Go through the RB tree quickly. */
    rb_node = mm->mm_rb.rb_node;

    while (rb_node) {
        struct vm_area_struct *vma_tmp;
        vma_tmp = rb_entry(rb_node, struct vm_area_struct, vm_rb);

        if (addr < vma_tmp->vm_end) {
            // TONY: if (vma_tmp->vm_start <= addr) vma = vma_tmp; //
this returns the correct 'vma' when vma is the first node (i.e., no
prev)
            rb_node = rb_node->rb_left;
        } else {
            prev = vma_tmp;
            if (!prev->vm_next || (addr < prev->vm_next->vm_end))
                break;
            rb_node = rb_node->rb_right;
        }
    }

out:
    *pprev = prev;
    return prev ? prev->vm_next : vma;
}

Is this a known issue and/or has this problem been addressed?
Also, please CC my email address with responses.

Thanks,
--tony

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Aim for Perfection!
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