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authorMing Lei <ming.lei@redhat.com>2020-05-08 11:17:55 +0300
committerJens Axboe <axboe@kernel.dk>2020-05-13 05:31:39 +0300
commitb7d6c30333239f77f8e51423064a623acc7fd127 (patch)
tree0f40462c0e231e405291ed5a2c32e0f9d6795ada /block/genhd.c
parentaa880ad690ab6d4c53934af85fb5a43e69ecb0f5 (diff)
downloadlinux-b7d6c30333239f77f8e51423064a623acc7fd127.tar.xz
block: fix use-after-free on cached last_lookup partition
delete_partition() clears the cached last_lookup partition. However the .last_lookup cache may be overwritten by one IO path after it is cleared from delete_partition(). Then another IO path may use the cached deleting partition after hd_struct_free() is called, then use-after-free is triggered on the cached partition. Fixes the issue by the following approach: 1) always get the partition's refcount via hd_struct_try_get() before setting .last_lookup 2) move clearing .last_lookup from delete_partition() to hd_struct_free() which is the release handle of the partition's percpu-refcount, so that no IO path can cache deleteing partition via .last_lookup. It is one candidate approach of Yufen's patch[1] which adds overhead in fast path by indirect lookup which may introduce one extra cacheline in IO path. Also this patch relies on percpu-refcount's protection, and it is easier to understand and verify. [1] https://lore.kernel.org/linux-block/20200109013551.GB9655@ming.t460p/T/#t Reported-by: Yufen Yu <yuyufen@huawei.com> Signed-off-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Christoph Hellwig <hch@infradead.org> Cc: Christoph Hellwig <hch@infradead.org> Cc: Hou Tao <houtao1@huawei.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/genhd.c')
-rw-r--r--block/genhd.c15
1 files changed, 12 insertions, 3 deletions
diff --git a/block/genhd.c b/block/genhd.c
index 27511b3d164d..af6cba2a9332 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -344,11 +344,12 @@ static inline int sector_in_part(struct hd_struct *part, sector_t sector)
* primarily used for stats accounting.
*
* CONTEXT:
- * RCU read locked. The returned partition pointer is valid only
- * while preemption is disabled.
+ * RCU read locked. The returned partition pointer is always valid
+ * because its refcount is grabbed.
*
* RETURNS:
* Found partition on success, part0 is returned if no partition matches
+ * or the matched partition is being deleted.
*/
struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
{
@@ -359,17 +360,25 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
ptbl = rcu_dereference(disk->part_tbl);
part = rcu_dereference(ptbl->last_lookup);
- if (part && sector_in_part(part, sector))
+ if (part && sector_in_part(part, sector) && hd_struct_try_get(part))
return part;
for (i = 1; i < ptbl->len; i++) {
part = rcu_dereference(ptbl->part[i]);
if (part && sector_in_part(part, sector)) {
+ /*
+ * only live partition can be cached for lookup,
+ * so use-after-free on cached & deleting partition
+ * can be avoided
+ */
+ if (!hd_struct_try_get(part))
+ break;
rcu_assign_pointer(ptbl->last_lookup, part);
return part;
}
}
+ hd_struct_get(&disk->part0);
return &disk->part0;
}