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io_uring/kbuf: Fix check of BID wrapping in provided buffers

Commit 3851d25c75ed0 ("io_uring: check for rollover of buffer ID when
providing buffers") introduced a check to prevent wrapping the BID
counter when sqe->off is provided, but it's off-by-one too
restrictive, rejecting the last possible BID (65534).

i.e., the following fails with -EINVAL.

io_uring_prep_provide_buffers(sqe, addr, size, 0xFFFF, 0, 0);

Fixes: 3851d25c75ed ("io_uring: check for rollover of buffer ID when providing buffers")
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
Link: https://lore.kernel.org/r/20231005000531.30800-2-krisman@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

authored by

Gabriel Krisman Bertazi and committed by
Jens Axboe ab69838e 922a2c78

+1 -1
+1 -1
io_uring/kbuf.c
··· 352 352 tmp = READ_ONCE(sqe->off); 353 353 if (tmp > USHRT_MAX) 354 354 return -E2BIG; 355 - if (tmp + p->nbufs >= USHRT_MAX) 355 + if (tmp + p->nbufs > USHRT_MAX) 356 356 return -EINVAL; 357 357 p->bid = tmp; 358 358 return 0;