nfc: llcp: avoid userspace overflow on invalid optlen

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nfc_llcp_getsockopt() casts optval to (u32 __user *) for put_user(), so
the kernel always stores 4 bytes regardless of the caller-supplied
optlen. The existing min_t(u32, len, sizeof(u32)) only clamps the length
reported back to userspace; it does not constrain the store. A call with
optlen < 4 therefore writes past the user buffer, violating the
getsockopt(2) contract for all five supported optnames.

Reject any call with optlen < sizeof(u32) up front. 'len' is int, so a
plain size comparison would promote a negative optlen to size_t and slip
past the check; an explicit 'len < 0' test is added first to catch
negative values before the size compare.

Fixes: 26fd76cab2 ("NFC: llcp: Implement socket options")
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260521-fix_llc-v2-1-ab44cc09179c@debian.org
Signed-off-by: David Heidelberg <david@ixit.cz>

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Breno Leitao 2026-05-21 07:32:09 -07:00 • committed by David Heidelberg

parent db2ddb8714

commit 99985bfa83

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net/nfc/llcp_sock.c

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