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Subject[PATCH 31/31] swapfile: avoid NULL pointer dereference in swapon when s_bdev is NULL
Date
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 is not
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 | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)

Index: mmotm/mm/swapfile.c
===================================================================
--- mmotm.orig/mm/swapfile.c
+++ mmotm/mm/swapfile.c
@@ -160,10 +160,12 @@ static int discard_swap(struct swap_info
continue;
}

- err = blkdev_issue_discard(si->bdev, start_block,
+ if (si->bdev) {
+ err = blkdev_issue_discard(si->bdev, start_block,
nr_blocks, GFP_KERNEL);
- if (err)
- break;
+ if (err)
+ break;
+ }

cond_resched();
}
@@ -199,9 +201,11 @@ static void discard_swap_cluster(struct

start_block <<= PAGE_SHIFT - 9;
nr_blocks <<= PAGE_SHIFT - 9;
- if (blkdev_issue_discard(si->bdev, start_block,
+ if (si->bdev) {
+ if (blkdev_issue_discard(si->bdev, start_block,
nr_blocks, GFP_NOIO))
- break;
+ break;
+ }
}

lh = se->list.next;
@@ -1991,12 +1995,14 @@ SYSCALL_DEFINE2(swapon, const char __use
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);

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