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SubjectRe: [PATCH] swapfile: avoid NULL pointer dereference in swapon when s_bdev is NULL
On Tue, Sep 29 2009, Suresh Jayaraman wrote:
> While testing Swap over NFS patchset, I noticed an oops that was triggered
> during swapon. Investigating further, the NULL pointer deference is due to the
> SSD device check/optimization in the swapon code that assumes s_bdev could never
> be NULL.
>
> inode->i_sb->s_bdev could be NULL in a few cases. For e.g. one such case is
> loopback NFS mount, there could be others as well. Fix this by ensuring s_bdev
> is not NULL before we try to deference s_bdev.
>
> Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
> ---
> mm/swapfile.c | 12 +++++++-----
> 1 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 4de7f02..a1bc6b9 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1974,12 +1974,14 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
> goto bad_swap;
> }
>
> - if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
> - p->flags |= SWP_SOLIDSTATE;
> - p->cluster_next = 1 + (random32() % p->highest_bit);
> + if (p->bdev) {
> + if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
> + p->flags |= SWP_SOLIDSTATE;
> + p->cluster_next = 1 + (random32() % p->highest_bit);
> + }
> + if (discard_swap(p) == 0)
> + p->flags |= SWP_DISCARDABLE;
> }
> - if (discard_swap(p) == 0)
> - p->flags |= SWP_DISCARDABLE;
>
> mutex_lock(&swapon_mutex);
> spin_lock(&swap_lock);

Thanks for the patch, looks correct.

--
Jens Axboe



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