aio: sanitize the limit checking in io_submit(2)

as it is, the logics in native io_submit(2) is "if asked for
more than LONG_MAX/sizeof(pointer) iocbs to submit, don't
bother with more than LONG_MAX/sizeof(pointer)" (i.e.
512M requests on 32bit and 1E requests on 64bit) while
compat io_submit(2) goes with "stop after the first
PAGE_SIZE/sizeof(pointer) iocbs", i.e. 1K or so.  Which is
	* inconsistent
	* *way* too much in native case
	* possibly too little in compat one
and
	* wrong anyway, since the natural point where we
ought to stop bothering is ctx->nr_events

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 6 insertions, 8 deletions

diff --git a/fs/aio.c b/fs/aio.c
index da859574c953..b850e92ee0d5 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1841,15 +1841,15 @@ SYSCALL_DEFINE3(io_submit, aio_context_t, ctx_id, long, nr,
         if (unlikely(nr < 0))
                 return -EINVAL;
 
-        if (unlikely(nr > LONG_MAX/sizeof(*iocbpp)))
-                nr = LONG_MAX/sizeof(*iocbpp);
-
         ctx = lookup_ioctx(ctx_id);
         if (unlikely(!ctx)) {
                 pr_debug("EINVAL: invalid context id\n");
                 return -EINVAL;
         }
 
+        if (nr > ctx->nr_events)
+                nr = ctx->nr_events;
+
         blk_start_plug(&plug);
         for (i = 0; i < nr; i++) {
                 struct iocb __user *user_iocb;
@@ -1870,8 +1870,6 @@ SYSCALL_DEFINE3(io_submit, aio_context_t, ctx_id, long, nr,
 }
 
 #ifdef CONFIG_COMPAT
-#define MAX_AIO_SUBMITS         (PAGE_SIZE/sizeof(struct iocb *))
-
 COMPAT_SYSCALL_DEFINE3(io_submit, compat_aio_context_t, ctx_id,
                        int, nr, compat_uptr_t __user *, iocbpp)
 {
@@ -1883,15 +1881,15 @@ COMPAT_SYSCALL_DEFINE3(io_submit, compat_aio_context_t, ctx_id,
         if (unlikely(nr < 0))
                 return -EINVAL;
 
-        if (nr > MAX_AIO_SUBMITS)
-                nr = MAX_AIO_SUBMITS;
-
         ctx = lookup_ioctx(ctx_id);
         if (unlikely(!ctx)) {
                 pr_debug("EINVAL: invalid context id\n");
                 return -EINVAL;
         }
 
+        if (nr > ctx->nr_events)
+                nr = ctx->nr_events;
+
         blk_start_plug(&plug);
         for (i = 0; i < nr; i++) {
                 compat_uptr_t user_iocb;