block: fix bio_alloc_bioset slowpath GFP handling

bio_alloc_bioset() first strips __GFP_DIRECT_RECLAIM from the optimistic
fast allocation attempt with try_alloc_gfp(). If that fast path fails,
the slowpath checks saved_gfp to decide whether blocking allocation is
allowed, but then still calls mempool_alloc() with the stripped gfp mask.
That can lead to a NULL bio pointer being passed into bio_init().

Fix the slowpath by using saved_gfp for the bio and bvec mempool
allocations.

Fixes: b520c4eef83d ("block: split bio_alloc_bioset more clearly into a fast and slowpath")
Reported-by: syzbot+09ddb593eea76a158f42@syzkaller.appspotmail.com
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/p01.gc6e9ad5845ad.ttca29g@ub.hpns
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/bio.c b/block/bio.c
index 5057047194c49880e94b0e532cbc219f128ed478..77067fa346d3585a354723d2255feb1f15a775ad 100644 (file)
--- a/block/bio.c
+++ b/block/bio.c
@@ -581,11 +581,11 @@ struct bio *bio_alloc_bioset(struct block_device *bdev, unsigned short nr_vecs,
                 */
                opf &= ~REQ_ALLOC_CACHE;
 
-               p = mempool_alloc(&bs->bio_pool, gfp);
+               p = mempool_alloc(&bs->bio_pool, saved_gfp);
                bio = p + bs->front_pad;
                if (nr_vecs > BIO_INLINE_VECS) {
                        nr_vecs = BIO_MAX_VECS;
-                       bvecs = mempool_alloc(&bs->bvec_pool, gfp);
+                       bvecs = mempool_alloc(&bs->bvec_pool, saved_gfp);
                }
        }