From: Bryam Vargas fdp_nci_i2c_read() takes the next packet length from two device-supplied bytes and never validates it. The value is a u16 used as the i2c_master_recv() count into a 261-byte on-stack buffer: a malicious, counterfeit or malfunctioning controller (or an i2c bus interposer) can drive it far past the buffer for a stack out-of-bounds write that clobbers the canary and return address, or below the minimum frame size (directly, or by truncating the computed sum) so the header/LRC strip and the next length read run past a short receive. Reject a length outside [FDP_NCI_I2C_MIN_PAYLOAD, FDP_NCI_I2C_MAX_PAYLOAD], as a corrupted packet already is, and force resynchronization. The same loop allocates one data skb per iteration and assumes a length packet followed by a data packet; a device that sends two data packets in one call leaks the first skb when the second allocation overwrites it. Free a previously allocated skb before allocating the next. Fixes: a06347c04c13 ("NFC: Add Intel Fields Peak NFC solution driver") Cc: stable@vger.kernel.org Suggested-by: Simon Horman Signed-off-by: Bryam Vargas --- v3: - Rebase on current net; no code change since v2. Doruk Tan Ozturk independently found the same missing bound (0sec, https://lore.kernel.org/all/20260720132133.69635-1-doruk@0sec.ai) and noted there that this v2 is the more complete fix -- it also rejects the sub-minimum length Simon flagged and closes the skb leak. Reposting now that the driver has an active maintainer. v2: https://lore.kernel.org/all/20260616-b4-disp-b1f8ab4c-v2-1-2d1fe5955325@proton.me v2: - Also reject next_read_size < FDP_NCI_I2C_MIN_PAYLOAD, not just > FDP_NCI_I2C_MAX_PAYLOAD (Simon Horman). The small value is reachable both directly (tmp[2] == 0 && tmp[3] < 2) and through the u16 truncation of the computed sum (e.g. 0xff,0xff -> 65538 -> 2); a single range check on the stored value covers both, and also keeps the next length-field read from running on stale buffer bytes. - Fold in a fix for an skb leak in the same function (two data packets in one call overwrite and leak the first skb). v1: https://lore.kernel.org/all/20260615-b4-disp-f42dce2d-v1-1-186ff3dcbf37@proton.me Reproduced in-kernel on x86-64 (Linux 7.1.0-rc5, CONFIG_KASAN_STACK=y) with a faithful port of the read loop, and at full device magnitude with a userspace AddressSanitizer model: Stack OOB write A no bound, next_read_size 281 -> 20 B past tmp[261]: BUG: KASAN: stack-out-of-bounds in i2c_master_recv... Write of size 281 ... This frame has 1 object: [48, 309) 'tmp' B bounded to <= FDP_NCI_I2C_MAX_PAYLOAD: no KASAN report C well-formed (len 5): no KASAN report ASan model, full u16 next_read_size = 65535 -> 65274-byte stack-buffer-overflow WRITE on both -m32 and -m64; bounded build clean. skb leak (slabinfo active-object delta over 20000 reads, two data packets each, measured after a slab shrink) without the fix: skbuff_head_cache +20047, skbuff_small_head +20057 (one orphaned skb per call, unreclaimable) with the fix: ~0 --- drivers/nfc/fdp/i2c.c | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/drivers/nfc/fdp/i2c.c b/drivers/nfc/fdp/i2c.c index c1896a1d978c..f292e7f37456 100644 --- a/drivers/nfc/fdp/i2c.c +++ b/drivers/nfc/fdp/i2c.c @@ -166,9 +166,36 @@ static int fdp_nci_i2c_read(struct fdp_i2c_phy *phy, struct sk_buff **skb) /* Packet that contains a length */ if (tmp[0] == 0 && tmp[1] == 0) { phy->next_read_size = (tmp[2] << 8) + tmp[3] + 3; + + /* + * next_read_size is taken from the device and is used + * as the i2c_master_recv() count for the next packet + * and as the data skb size. A value above the receive + * buffer overflows tmp[]; one below the minimum frame + * size runs the header/LRC strip and the length-field + * read past a short receive. Either way the packet is + * corrupt: drop it and force resynchronization. + */ + if (phy->next_read_size < FDP_NCI_I2C_MIN_PAYLOAD || + phy->next_read_size > FDP_NCI_I2C_MAX_PAYLOAD) { + dev_dbg(&client->dev, "%s: corrupted packet\n", + __func__); + phy->next_read_size = FDP_NCI_I2C_MIN_PAYLOAD; + goto flush; + } } else { phy->next_read_size = FDP_NCI_I2C_MIN_PAYLOAD; + /* + * Only one data packet is delivered per call; if the + * device sends another, do not overwrite and leak the + * skb allocated for the previous one. + */ + if (*skb) { + kfree_skb(*skb); + *skb = NULL; + } + *skb = alloc_skb(len, GFP_KERNEL); if (*skb == NULL) { r = -ENOMEM; --- base-commit: 78f75d632f74b8de0f081a128588f7c37d0d1164 change-id: 20260724-b4-disp-e8ec6012-b488d7a20266 Best regards, -- Bryam Vargas