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See http://www.infradead.org/rpr.html X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 9D4BB1C0007 X-Rspam-User: X-Stat-Signature: kux5waqsqihecbq5o4gmprun1n5z1cnz X-HE-Tag: 1745213061-234408 X-HE-Meta: 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 5nW9PUj/ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Apr 18, 2025 at 05:38:23PM +0800, Yu Kuai wrote: > From: Yu Kuai > > Currently, after fetching the page by xa_load() in IO path, there is no > protection and page can be freed concurrently by discard: Ah, I guess this helps with the race I mentioned in reply to the previous patch. Is the rcu_head in struct page available for use by subsystems freeing the page? > > cpu0 > brd_submit_bio > brd_do_bvec > page = brd_lookup_page > cpu1 > brd_submit_bio > brd_do_discard > page = __xa_erase() > __free_page() > // page UAF > > Fix the problem by protecting page with rcu. > > Fixes: 9ead7efc6f3f ("brd: implement discard support") > Signed-off-by: Yu Kuai > --- > drivers/block/brd.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/drivers/block/brd.c b/drivers/block/brd.c > index a6e4f005cb76..740ed13faaff 100644 > --- a/drivers/block/brd.c > +++ b/drivers/block/brd.c > @@ -208,6 +208,7 @@ static int brd_do_bvec(struct brd_device *brd, struct page *page, > goto out; > } > > + rcu_read_lock(); > mem = kmap_local_page(page); > if (!op_is_write(opf)) { > copy_from_brd(mem + off, brd, sector, len); > @@ -217,11 +218,19 @@ static int brd_do_bvec(struct brd_device *brd, struct page *page, > copy_to_brd(brd, mem + off, sector, len); > } > kunmap_local(mem); > + rcu_read_unlock(); > > out: > return err; > } > > +static void brd_free_one_page(struct rcu_head *head) > +{ > + struct page *page = container_of(head, struct page, rcu_head); > + > + __free_page(page); > +} > + > static void brd_do_discard(struct brd_device *brd, sector_t sector, u32 size) > { > sector_t aligned_sector = (sector + PAGE_SECTORS) & ~PAGE_SECTORS; > @@ -232,7 +241,7 @@ static void brd_do_discard(struct brd_device *brd, sector_t sector, u32 size) > while (size >= PAGE_SIZE && aligned_sector < rd_size * 2) { > page = __xa_erase(&brd->brd_pages, aligned_sector >> PAGE_SECTORS_SHIFT); > if (page) { > - __free_page(page); > + call_rcu(&page->rcu_head, brd_free_one_page); > brd->brd_nr_pages--; > } > aligned_sector += PAGE_SECTORS; > -- > 2.39.2 > > ---end quoted text---