From a653c01ce447f10c36b901646888c0330363af4f Mon Sep 17 00:00:00 2001 From: Pengpeng Hou Date: Wed, 15 Jul 2026 16:44:05 +0800 Subject: [PATCH] nfc: st21nfca: validate received frame size st21nfca_hci_i2c_repack() trims a received frame at its EOF marker before removing byte stuffing. It then assumes the truncated frame contains the LLC header and two CRC bytes, and it unconditionally reads the byte after an escape marker. A malformed frame can place EOF immediately after the start marker or can end its data portion with an escape marker. The former leaves too few bytes for check_crc(), while the latter makes the unstuffing loop read past the current skb length. Require the minimum framing bytes both before and after unstuffing. Use separate input and output cursors while removing byte stuffing, and reject an escape marker without its encoded byte. This keeps malformed frames within the received frame boundary before CRC processing. Fixes: 3096e25a3e40 ("NFC: st21nfca: Fix incorrect byte stuffing revocation") Signed-off-by: Pengpeng Hou Link: https://patch.msgid.link/20260715084405.41546-1-pengpeng@iscas.ac.cn Signed-off-by: David Heidelberg --- drivers/nfc/st21nfca/i2c.c | 29 +++++++++++++++++++---------- 1 file changed, 19 insertions(+), 10 deletions(-) diff --git a/drivers/nfc/st21nfca/i2c.c b/drivers/nfc/st21nfca/i2c.c index a4c93ff7c5b0..0f44c783bd04 100644 --- a/drivers/nfc/st21nfca/i2c.c +++ b/drivers/nfc/st21nfca/i2c.c @@ -289,27 +289,36 @@ static int check_crc(u8 *buf, int buflen) */ static int st21nfca_hci_i2c_repack(struct sk_buff *skb) { - int i, j, r, size; + int read, write, r, size; - if (skb->len < 1 || (skb->len > 1 && skb->data[1] != 0)) + if (skb->len < ST21NFCA_FRAME_HEADROOM || + !IS_START_OF_FRAME(skb->data)) return -EBADMSG; size = get_frame_size(skb->data, skb->len); if (size > 0) { + if (size < ST21NFCA_FRAME_HEADROOM + 2) + return -EBADMSG; + skb_trim(skb, size); /* remove ST21NFCA byte stuffing for upper layer */ - for (i = 1, j = 0; i < skb->len; i++) { - if (skb->data[i + j] == + for (read = 1, write = 1; read < skb->len;) { + if (skb->data[read] == (u8) ST21NFCA_ESCAPE_BYTE_STUFFING) { - skb->data[i] = skb->data[i + j + 1] - | ST21NFCA_BYTE_STUFFING_MASK; - i++; - j++; + if (read + 1 == skb->len) + return -EBADMSG; + + skb->data[write++] = skb->data[read + 1] + | ST21NFCA_BYTE_STUFFING_MASK; + read += 2; + } else { + skb->data[write++] = skb->data[read++]; } - skb->data[i] = skb->data[i + j]; } /* remove byte stuffing useless byte */ - skb_trim(skb, i - j); + skb_trim(skb, write); + if (skb->len < ST21NFCA_FRAME_HEADROOM + 2) + return -EBADMSG; /* remove ST21NFCA_SOF_EOF from head */ skb_pull(skb, 1);