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authorLinus Torvalds <torvalds@linux-foundation.org>2019-03-03 14:23:33 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2019-03-04 10:32:48 -0800
commit84c4e1f89fefe70554da0ab33be72c9be7994379 (patch)
tree5c7132d99ea274df269232f530981b8a365ddb58 /fs/aio.c
parent00c42373d3970b354948ba3b24a34501b1a2505f (diff)
downloadlinux-stericsson-84c4e1f89fefe70554da0ab33be72c9be7994379.tar.gz
aio: simplify - and fix - fget/fput for io_submit()
Al Viro root-caused a race where the IOCB_CMD_POLL handling of fget/fput() could cause us to access the file pointer after it had already been freed: "In more details - normally IOCB_CMD_POLL handling looks so: 1) io_submit(2) allocates aio_kiocb instance and passes it to aio_poll() 2) aio_poll() resolves the descriptor to struct file by req->file = fget(iocb->aio_fildes) 3) aio_poll() sets ->woken to false and raises ->ki_refcnt of that aio_kiocb to 2 (bumps by 1, that is). 4) aio_poll() calls vfs_poll(). After sanity checks (basically, "poll_wait() had been called and only once") it locks the queue. That's what the extra reference to iocb had been for - we know we can safely access it. 5) With queue locked, we check if ->woken has already been set to true (by aio_poll_wake()) and, if it had been, we unlock the queue, drop a reference to aio_kiocb and bugger off - at that point it's a responsibility to aio_poll_wake() and the stuff called/scheduled by it. That code will drop the reference to file in req->file, along with the other reference to our aio_kiocb. 6) otherwise, we see whether we need to wait. If we do, we unlock the queue, drop one reference to aio_kiocb and go away - eventual wakeup (or cancel) will deal with the reference to file and with the other reference to aio_kiocb 7) otherwise we remove ourselves from waitqueue (still under the queue lock), so that wakeup won't get us. No async activity will be happening, so we can safely drop req->file and iocb ourselves. If wakeup happens while we are in vfs_poll(), we are fine - aio_kiocb won't get freed under us, so we can do all the checks and locking safely. And we don't touch ->file if we detect that case. However, vfs_poll() most certainly *does* touch the file it had been given. So wakeup coming while we are still in ->poll() might end up doing fput() on that file. That case is not too rare, and usually we are saved by the still present reference from descriptor table - that fput() is not the final one. But if another thread closes that descriptor right after our fget() and wakeup does happen before ->poll() returns, we are in trouble - final fput() done while we are in the middle of a method: Al also wrote a patch to take an extra reference to the file descriptor to fix this, but I instead suggested we just streamline the whole file pointer handling by submit_io() so that the generic aio submission code simply keeps the file pointer around until the aio has completed. Fixes: bfe4037e722e ("aio: implement IOCB_CMD_POLL") Acked-by: Al Viro <viro@zeniv.linux.org.uk> Reported-by: syzbot+503d4cc169fcec1cb18c@syzkaller.appspotmail.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/aio.c')
-rw-r--r--fs/aio.c72
1 files changed, 29 insertions, 43 deletions
diff --git a/fs/aio.c b/fs/aio.c
index aaaaf4d12c73..82c08422b0f4 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -167,9 +167,13 @@ struct kioctx {
unsigned id;
};
+/*
+ * First field must be the file pointer in all the
+ * iocb unions! See also 'struct kiocb' in <linux/fs.h>
+ */
struct fsync_iocb {
- struct work_struct work;
struct file *file;
+ struct work_struct work;
bool datasync;
};
@@ -183,8 +187,15 @@ struct poll_iocb {
struct work_struct work;
};
+/*
+ * NOTE! Each of the iocb union members has the file pointer
+ * as the first entry in their struct definition. So you can
+ * access the file pointer through any of the sub-structs,
+ * or directly as just 'ki_filp' in this struct.
+ */
struct aio_kiocb {
union {
+ struct file *ki_filp;
struct kiocb rw;
struct fsync_iocb fsync;
struct poll_iocb poll;
@@ -1060,6 +1071,8 @@ static inline void iocb_put(struct aio_kiocb *iocb)
{
if (refcount_read(&iocb->ki_refcnt) == 0 ||
refcount_dec_and_test(&iocb->ki_refcnt)) {
+ if (iocb->ki_filp)
+ fput(iocb->ki_filp);
percpu_ref_put(&iocb->ki_ctx->reqs);
kmem_cache_free(kiocb_cachep, iocb);
}
@@ -1424,7 +1437,6 @@ static void aio_complete_rw(struct kiocb *kiocb, long res, long res2)
file_end_write(kiocb->ki_filp);
}
- fput(kiocb->ki_filp);
aio_complete(iocb, res, res2);
}
@@ -1432,9 +1444,6 @@ static int aio_prep_rw(struct kiocb *req, const struct iocb *iocb)
{
int ret;
- req->ki_filp = fget(iocb->aio_fildes);
- if (unlikely(!req->ki_filp))
- return -EBADF;
req->ki_complete = aio_complete_rw;
req->private = NULL;
req->ki_pos = iocb->aio_offset;
@@ -1451,7 +1460,7 @@ static int aio_prep_rw(struct kiocb *req, const struct iocb *iocb)
ret = ioprio_check_cap(iocb->aio_reqprio);
if (ret) {
pr_debug("aio ioprio check cap error: %d\n", ret);
- goto out_fput;
+ return ret;
}
req->ki_ioprio = iocb->aio_reqprio;
@@ -1460,14 +1469,10 @@ static int aio_prep_rw(struct kiocb *req, const struct iocb *iocb)
ret = kiocb_set_rw_flags(req, iocb->aio_rw_flags);
if (unlikely(ret))
- goto out_fput;
+ return ret;
req->ki_flags &= ~IOCB_HIPRI; /* no one is going to poll for this I/O */
return 0;
-
-out_fput:
- fput(req->ki_filp);
- return ret;
}
static int aio_setup_rw(int rw, const struct iocb *iocb, struct iovec **iovec,
@@ -1521,24 +1526,19 @@ static ssize_t aio_read(struct kiocb *req, const struct iocb *iocb,
if (ret)
return ret;
file = req->ki_filp;
-
- ret = -EBADF;
if (unlikely(!(file->f_mode & FMODE_READ)))
- goto out_fput;
+ return -EBADF;
ret = -EINVAL;
if (unlikely(!file->f_op->read_iter))
- goto out_fput;
+ return -EINVAL;
ret = aio_setup_rw(READ, iocb, &iovec, vectored, compat, &iter);
if (ret)
- goto out_fput;
+ return ret;
ret = rw_verify_area(READ, file, &req->ki_pos, iov_iter_count(&iter));
if (!ret)
aio_rw_done(req, call_read_iter(file, req, &iter));
kfree(iovec);
-out_fput:
- if (unlikely(ret))
- fput(file);
return ret;
}
@@ -1555,16 +1555,14 @@ static ssize_t aio_write(struct kiocb *req, const struct iocb *iocb,
return ret;
file = req->ki_filp;
- ret = -EBADF;
if (unlikely(!(file->f_mode & FMODE_WRITE)))
- goto out_fput;
- ret = -EINVAL;
+ return -EBADF;
if (unlikely(!file->f_op->write_iter))
- goto out_fput;
+ return -EINVAL;
ret = aio_setup_rw(WRITE, iocb, &iovec, vectored, compat, &iter);
if (ret)
- goto out_fput;
+ return ret;
ret = rw_verify_area(WRITE, file, &req->ki_pos, iov_iter_count(&iter));
if (!ret) {
/*
@@ -1582,9 +1580,6 @@ static ssize_t aio_write(struct kiocb *req, const struct iocb *iocb,
aio_rw_done(req, call_write_iter(file, req, &iter));
}
kfree(iovec);
-out_fput:
- if (unlikely(ret))
- fput(file);
return ret;
}
@@ -1594,7 +1589,6 @@ static void aio_fsync_work(struct work_struct *work)
int ret;
ret = vfs_fsync(req->file, req->datasync);
- fput(req->file);
aio_complete(container_of(req, struct aio_kiocb, fsync), ret, 0);
}
@@ -1605,13 +1599,8 @@ static int aio_fsync(struct fsync_iocb *req, const struct iocb *iocb,
iocb->aio_rw_flags))
return -EINVAL;
- req->file = fget(iocb->aio_fildes);
- if (unlikely(!req->file))
- return -EBADF;
- if (unlikely(!req->file->f_op->fsync)) {
- fput(req->file);
+ if (unlikely(!req->file->f_op->fsync))
return -EINVAL;
- }
req->datasync = datasync;
INIT_WORK(&req->work, aio_fsync_work);
@@ -1621,10 +1610,7 @@ static int aio_fsync(struct fsync_iocb *req, const struct iocb *iocb,
static inline void aio_poll_complete(struct aio_kiocb *iocb, __poll_t mask)
{
- struct file *file = iocb->poll.file;
-
aio_complete(iocb, mangle_poll(mask), 0);
- fput(file);
}
static void aio_poll_complete_work(struct work_struct *work)
@@ -1743,9 +1729,6 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, const struct iocb *iocb)
INIT_WORK(&req->work, aio_poll_complete_work);
req->events = demangle_poll(iocb->aio_buf) | EPOLLERR | EPOLLHUP;
- req->file = fget(iocb->aio_fildes);
- if (unlikely(!req->file))
- return -EBADF;
req->head = NULL;
req->woken = false;
@@ -1788,10 +1771,8 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, const struct iocb *iocb)
spin_unlock_irq(&ctx->ctx_lock);
out:
- if (unlikely(apt.error)) {
- fput(req->file);
+ if (unlikely(apt.error))
return apt.error;
- }
if (mask)
aio_poll_complete(aiocb, mask);
@@ -1829,6 +1810,11 @@ static int __io_submit_one(struct kioctx *ctx, const struct iocb *iocb,
if (unlikely(!req))
goto out_put_reqs_available;
+ req->ki_filp = fget(iocb->aio_fildes);
+ ret = -EBADF;
+ if (unlikely(!req->ki_filp))
+ goto out_put_req;
+
if (iocb->aio_flags & IOCB_FLAG_RESFD) {
/*
* If the IOCB_FLAG_RESFD flag of aio_flags is set, get an