io_uring/kbuf: sanitize peek buffer setup

Harden the buffer peeking a bit, by adding a sanity check for it having
a valid size. Outside of that, arg->max_len is a size_t, though it's
only ever set to a 32-bit value (as it's governed by MAX_RW_COUNT).
Bump our needed check to a size_t so we know it fits. Finally, cap the
calculated needed iov value to the PEEK_MAX_IMPORT, which is the
maximum number of segments that should be peeked.

Fixes: 35c8711c8fc4 ("io_uring/kbuf: add helpers for getting/peeking multiple buffers")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index c95dc1736dd93019040230aca6126d7b8475dab8..1af2bd56af44ac496fd56f327e596730844ceb3f 100644 (file)
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -218,10 +218,13 @@ static int io_ring_buffers_peek(struct io_kiocb *req, struct buf_sel_arg *arg,
 
        buf = io_ring_head_to_buf(br, head, bl->mask);
        if (arg->max_len) {
-               int needed;
+               u32 len = READ_ONCE(buf->len);
+               size_t needed;
 
-               needed = (arg->max_len + buf->len - 1) / buf->len;
-               needed = min(needed, PEEK_MAX_IMPORT);
+               if (unlikely(!len))
+                       return -ENOBUFS;
+               needed = (arg->max_len + len - 1) / len;
+               needed = min_not_zero(needed, (size_t) PEEK_MAX_IMPORT);
                if (nr_avail > needed)
                        nr_avail = needed;
        }