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5c14a19d5b
s3fwrn82_uart_read() reports the number of accepted bytes to the serdev
core. The current code consumes bytes into recv_skb and may already
deliver a complete frame before allocating a fresh receive buffer.
If that alloc_skb() fails, the callback returns 0 even though it has
already consumed bytes, and it leaves recv_skb as NULL for the next
receive callback. That breaks the receive_buf() accounting contract and
can also lead to a NULL dereference on the next skb_put_u8().
Allocate the receive skb lazily before consuming the next byte instead.
If allocation fails, return the number of bytes already accepted.
Fixes: 3f52c2cb7e ("nfc: s3fwrn5: Support a UART interface")
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Link: https://patch.msgid.link/20260402042148.65236-1-pengpeng@iscas.ac.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>