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mptcp: sockopt: info: stop early if no buffer

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Up to recently, it has been recommended to use getsockopt(MPTCP_INFO) to
check if a fallback to TCP happened, or if the client requested to use
MPTCP.

In this case, the userspace app is only interested by the returned value
of the getsocktop() call, and can then give 0 for the option length, and
NULL for the buffer address. An easy optimisation is then to stop early,
and avoid filling a local buffer -- which now requires two different
locks -- if it is not needed.

Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20240514011335.176158-4-martineau@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Matthieu Baerts (NGI0) 2024-05-13 18:13:27 -07:00 committed by Jakub Kicinski
parent bd11dc4fb9
commit ce5f6f71b0
1 changed files with 4 additions and 0 deletions
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4
net/mptcp/sockopt.c
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@ -999,6 +999,10 @@ static int mptcp_getsockopt_info(struct mptcp_sock *msk, char __user *optval, in
if (get_user(len, optlen))
return -EFAULT;
/* When used only to check if a fallback to TCP happened. */
if (len == 0)
return 0;
len = min_t(unsigned int, len, sizeof(struct mptcp_info));
mptcp_diag_fill_info(msk, &m_info);