[Xen-devel] [PATCH 2/2] xen-blkfront: implement safe version of llist_for_each_entry

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Implement a safe version of llist_for_each_entry, and use it in
blkif_free. Previously grants where freed while iterating the list,
which lead to dereferences when trying to fetch the next item.

Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxx
---
 drivers/block/xen-blkfront.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 96e9b00..df21b05 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -143,6 +143,13 @@ static DEFINE_SPINLOCK(minor_lock);
 
 #define DEV_NAME       "xvd"   /* name in /dev */
 
+#define llist_for_each_entry_safe(pos, n, node, member)                \
+       for ((pos) = llist_entry((node), typeof(*(pos)), member),       \
+            (n) = (pos)->member.next;                                  \
+            &(pos)->member != NULL;                                    \
+            (pos) = llist_entry(n, typeof(*(pos)), member),            \
+            (n) = (&(pos)->member != NULL) ? (pos)->member.next : NULL)
+
 static int get_id_from_freelist(struct blkfront_info *info)
 {
        unsigned long free = info->shadow_free;
@@ -792,6 +799,7 @@ static void blkif_free(struct blkfront_info *info, int 
suspend)
 {
        struct llist_node *all_gnts;
        struct grant *persistent_gnt;
+       struct llist_node *n;
 
        /* Prevent new requests being issued until we fix things up. */
        spin_lock_irq(&info->io_lock);
@@ -804,7 +812,7 @@ static void blkif_free(struct blkfront_info *info, int 
suspend)
        /* Remove all persistent grants */
        if (info->persistent_gnts_c) {
                all_gnts = llist_del_all(&info->persistent_gnts);
-               llist_for_each_entry(persistent_gnt, all_gnts, node) {
+               llist_for_each_entry_safe(persistent_gnt, n, all_gnts, node) {
                        gnttab_end_foreign_access(persistent_gnt->gref, 0, 0UL);
                        __free_page(pfn_to_page(persistent_gnt->pfn));
                        kfree(persistent_gnt);
-- 
1.7.7.5 (Apple Git-26)


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