[PATCH AUTOSEL 6.6 21/32] io_uring: use fget/fput consistently

Sasha Levin
2023-12-04T20:35:30Z

From: Jens Axboe <axboe@kernel.dk>

[ Upstream commit 73363c262d6a7d26063da96610f61baf69a70f7c ]

Normally within a syscall it's fine to use fdget/fdput for grabbing a
file from the file table, and it's fine within io_uring as well. We do
that via io_uring_enter(2), io_uring_register(2), and then also for
cancel which is invoked from the latter. io_uring cannot close its own
file descriptors as that is explicitly rejected, and for the cancel
side of things, the file itself is just used as a lookup cookie.

However, it is more prudent to ensure that full references are always
grabbed. For anything threaded, either explicitly in the application
itself or through use of the io-wq worker threads, this is what happens
anyway. Generalize it and use fget/fput throughout.

Also see the below link for more details.

Link: https://lore.kernel.org/io-uring/CAG48ez1htVSO3TqmrF8QcX2WFuYTRM-VZ_N10i-VZgbtg=NNqw@mail.gmail.com/
Suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
io_uring/cancel.c | 11 ++++++-----
io_uring/io_uring.c | 36 ++++++++++++++++++------------------
2 files changed, 24 insertions(+), 23 deletions(-)

diff --git a/io_uring/cancel.c b/io_uring/cancel.c
index 7b23607cf4afd..a5d51471feebb 100644
--- a/io_uring/cancel.c
+++ b/io_uring/cancel.c
@@ -263,7 +263,7 @@ int io_sync_cancel(struct io_ring_ctx *ctx, void __user *arg)
};
ktime_t timeout = KTIME_MAX;
struct io_uring_sync_cancel_reg sc;
- struct fd f = { };
+ struct file *file = NULL;
DEFINE_WAIT(wait);
int ret, i;

@@ -285,10 +285,10 @@ int io_sync_cancel(struct io_ring_ctx *ctx, void __user *arg)
/* we can grab a normal file descriptor upfront */
if ((cd.flags & IORING_ASYNC_CANCEL_FD) &&
!(cd.flags & IORING_ASYNC_CANCEL_FD_FIXED)) {
- f = fdget(sc.fd);
- if (!f.file)
+ file = fget(sc.fd);
+ if (!file)
return -EBADF;
- cd.file = f.file;
+ cd.file = file;
}

ret = __io_sync_cancel(current->io_uring, &cd, sc.fd);
@@ -338,6 +338,7 @@ int io_sync_cancel(struct io_ring_ctx *ctx, void __user *arg)
if (ret == -ENOENT || ret > 0)
ret = 0;
out:
- fdput(f);
+ if (file)
+ fput(file);
return ret;
}
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 8d1bc6cdfe712..e27d970b140c3 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3603,7 +3603,7 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
size_t, argsz)
{
struct io_ring_ctx *ctx;
- struct fd f;
+ struct file *file;
long ret;

if (unlikely(flags & ~(IORING_ENTER_GETEVENTS | IORING_ENTER_SQ_WAKEUP |
@@ -3621,20 +3621,19 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
if (unlikely(!tctx || fd >= IO_RINGFD_REG_MAX))
return -EINVAL;
fd = array_index_nospec(fd, IO_RINGFD_REG_MAX);
- f.file = tctx->registered_rings[fd];
- f.flags = 0;
- if (unlikely(!f.file))
+ file = tctx->registered_rings[fd];
+ if (unlikely(!file))
return -EBADF;
} else {
- f = fdget(fd);
- if (unlikely(!f.file))
+ file = fget(fd);
+ if (unlikely(!file))
return -EBADF;
ret = -EOPNOTSUPP;
- if (unlikely(!io_is_uring_fops(f.file)))
+ if (unlikely(!io_is_uring_fops(file)))
goto out;
}

- ctx = f.file->private_data;
+ ctx = file->private_data;
ret = -EBADFD;
if (unlikely(ctx->flags & IORING_SETUP_R_DISABLED))
goto out;
@@ -3728,7 +3727,8 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
}
}
out:
- fdput(f);
+ if (!(flags & IORING_ENTER_REGISTERED_RING))
+ fput(file);
return ret;
}

@@ -4569,7 +4569,7 @@ SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
{
struct io_ring_ctx *ctx;
long ret = -EBADF;
- struct fd f;
+ struct file *file;
bool use_registered_ring;

use_registered_ring = !!(opcode & IORING_REGISTER_USE_REGISTERED_RING);
@@ -4588,27 +4588,27 @@ SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
if (unlikely(!tctx || fd >= IO_RINGFD_REG_MAX))
return -EINVAL;
fd = array_index_nospec(fd, IO_RINGFD_REG_MAX);
- f.file = tctx->registered_rings[fd];
- f.flags = 0;
- if (unlikely(!f.file))
+ file = tctx->registered_rings[fd];
+ if (unlikely(!file))
return -EBADF;
} else {
- f = fdget(fd);
- if (unlikely(!f.file))
+ file = fget(fd);
+ if (unlikely(!file))
return -EBADF;
ret = -EOPNOTSUPP;
- if (!io_is_uring_fops(f.file))
+ if (!io_is_uring_fops(file))
goto out_fput;
}

- ctx = f.file->private_data;
+ ctx = file->private_data;

mutex_lock(&ctx->uring_lock);
ret = __io_uring_register(ctx, opcode, arg, nr_args);
mutex_unlock(&ctx->uring_lock);
trace_io_uring_register(ctx, opcode, ctx->nr_user_files, ctx->nr_user_bufs, ret);
out_fput:
- fdput(f);
+ if (!use_registered_ring)
+ fput(file);
return ret;
}

--
2.42.0