From d1719f70d0a5b83b12786a7dbc5b9fe396469016 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Thu, 30 Jul 2020 13:43:53 -0600 Subject: io_uring: don't touch 'ctx' after installing file descriptor As soon as we install the file descriptor, we have to assume that it can get arbitrarily closed. We currently account memory (and note that we did) after installing the ring fd, which means that it could be a potential use-after-free condition if the fd is closed right after being installed, but before we fiddle with the ctx. In fact, syzbot reported this exact scenario: BUG: KASAN: use-after-free in io_account_mem fs/io_uring.c:7397 [inline] BUG: KASAN: use-after-free in io_uring_create fs/io_uring.c:8369 [inline] BUG: KASAN: use-after-free in io_uring_setup+0x2797/0x2910 fs/io_uring.c:8400 Read of size 1 at addr ffff888087a41044 by task syz-executor.5/18145 CPU: 0 PID: 18145 Comm: syz-executor.5 Not tainted 5.8.0-rc7-next-20200729-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x18f/0x20d lib/dump_stack.c:118 print_address_description.constprop.0.cold+0xae/0x497 mm/kasan/report.c:383 __kasan_report mm/kasan/report.c:513 [inline] kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530 io_account_mem fs/io_uring.c:7397 [inline] io_uring_create fs/io_uring.c:8369 [inline] io_uring_setup+0x2797/0x2910 fs/io_uring.c:8400 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x45c429 Code: 8d b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 5b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007f8f121d0c78 EFLAGS: 00000246 ORIG_RAX: 00000000000001a9 RAX: ffffffffffffffda RBX: 0000000000008540 RCX: 000000000045c429 RDX: 0000000000000000 RSI: 0000000020000040 RDI: 0000000000000196 RBP: 000000000078bf38 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 000000000078bf0c R13: 00007fff86698cff R14: 00007f8f121d19c0 R15: 000000000078bf0c Move the accounting of the ring used locked memory before we get and install the ring file descriptor. Cc: stable@vger.kernel.org Reported-by: syzbot+9d46305e76057f30c74e@syzkaller.appspotmail.com Fixes: 309758254ea6 ("io_uring: report pinned memory usage") Reviewed-by: Stefano Garzarella Signed-off-by: Jens Axboe --- fs/io_uring.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index fabf0b692384..33702f3b5af8 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -8329,6 +8329,15 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p, ret = -EFAULT; goto err; } + + /* + * Account memory _before_ installing the file descriptor. Once + * the descriptor is installed, it can get closed at any time. + */ + io_account_mem(ctx, ring_pages(p->sq_entries, p->cq_entries), + ACCT_LOCKED); + ctx->limit_mem = limit_mem; + /* * Install ring fd as the very last thing, so we don't risk someone * having closed it before we finish setup @@ -8338,9 +8347,6 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p, goto err; trace_io_uring_create(ret, ctx, p->sq_entries, p->cq_entries, p->flags); - io_account_mem(ctx, ring_pages(p->sq_entries, p->cq_entries), - ACCT_LOCKED); - ctx->limit_mem = limit_mem; return ret; err: io_ring_ctx_wait_and_kill(ctx); -- cgit v1.2.3