From: Peter Maydell <peter.mayd...@linaro.org> The smc91c111 uses packet numbers as an index into its internal s->data[][] array. Valid packet numbers are between 0 and 3, but the code does not generally check this, and there are various places where the guest can hand us an arbitrary packet number and cause an out-of-bounds access to the data array.
Add validation of packet numbers. The datasheet is not very helpful about how guest errors like this should be handled: it says nothing on the subject, and none of the documented error conditions are relevant. We choose to log the situation with LOG_GUEST_ERROR and silently ignore the attempted operation. In the places where we are about to access the data[][] array using a packet number and we know the number is valid because we got it from somewhere that has already validated, we add an assert() to document that belief. Cc: qemu-sta...@nongnu.org Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> Reviewed-by: Philippe Mathieu-Daudé <phi...@linaro.org> Message-ID: <20250228174802.1945417-2-peter.mayd...@linaro.org> Signed-off-by: Philippe Mathieu-Daudé <phi...@linaro.org> --- hw/net/smc91c111.c | 45 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+) diff --git a/hw/net/smc91c111.c b/hw/net/smc91c111.c index 0e13dfa18b2..2295c6acf25 100644 --- a/hw/net/smc91c111.c +++ b/hw/net/smc91c111.c @@ -118,6 +118,11 @@ static const VMStateDescription vmstate_smc91c111 = { #define RS_TOOSHORT 0x0400 #define RS_MULTICAST 0x0001 +static inline bool packetnum_valid(int packet_num) +{ + return packet_num >= 0 && packet_num < NUM_PACKETS; +} + /* Update interrupt status. */ static void smc91c111_update(smc91c111_state *s) { @@ -218,6 +223,17 @@ static void smc91c111_pop_tx_fifo_done(smc91c111_state *s) /* Release the memory allocated to a packet. */ static void smc91c111_release_packet(smc91c111_state *s, int packet) { + if (!packetnum_valid(packet)) { + /* + * Data sheet doesn't document behaviour in this guest error + * case, and there is no error status register to report it. + * Log and ignore the attempt. + */ + qemu_log_mask(LOG_GUEST_ERROR, + "smc91c111: attempt to release invalid packet %d\n", + packet); + return; + } s->allocated &= ~(1 << packet); if (s->tx_alloc == 0x80) smc91c111_tx_alloc(s); @@ -239,6 +255,8 @@ static void smc91c111_do_tx(smc91c111_state *s) return; for (i = 0; i < s->tx_fifo_len; i++) { packetnum = s->tx_fifo[i]; + /* queue_tx checked the packet number was valid */ + assert(packetnum_valid(packetnum)); p = &s->data[packetnum][0]; /* Set status word. */ *(p++) = 0x01; @@ -287,6 +305,17 @@ static void smc91c111_do_tx(smc91c111_state *s) /* Add a packet to the TX FIFO. */ static void smc91c111_queue_tx(smc91c111_state *s, int packet) { + if (!packetnum_valid(packet)) { + /* + * Datasheet doesn't document behaviour in this error case, and + * there's no error status register we could report it in. + * Log and ignore. + */ + qemu_log_mask(LOG_GUEST_ERROR, + "smc91c111: attempt to queue invalid packet %d\n", + packet); + return; + } if (s->tx_fifo_len == NUM_PACKETS) return; s->tx_fifo[s->tx_fifo_len++] = packet; @@ -457,6 +486,13 @@ static void smc91c111_writeb(void *opaque, hwaddr offset, n = s->rx_fifo[0]; else n = s->packet_num; + if (!packetnum_valid(n)) { + /* Datasheet doesn't document what to do here */ + qemu_log_mask(LOG_GUEST_ERROR, + "smc91c111: attempt to write data to invalid packet %d\n", + n); + return; + } p = s->ptr & 0x07ff; if (s->ptr & 0x4000) { s->ptr = (s->ptr & 0xf800) | ((s->ptr + 1) & 0x7ff); @@ -605,6 +641,13 @@ static uint32_t smc91c111_readb(void *opaque, hwaddr offset) n = s->rx_fifo[0]; else n = s->packet_num; + if (!packetnum_valid(n)) { + /* Datasheet doesn't document what to do here */ + qemu_log_mask(LOG_GUEST_ERROR, + "smc91c111: attempt to read data from invalid packet %d\n", + n); + return 0; + } p = s->ptr & 0x07ff; if (s->ptr & 0x4000) { s->ptr = (s->ptr & 0xf800) | ((s->ptr + 1) & 0x07ff); @@ -713,6 +756,8 @@ static ssize_t smc91c111_receive(NetClientState *nc, const uint8_t *buf, size_t return -1; s->rx_fifo[s->rx_fifo_len++] = packetnum; + /* allocate_packet() will not hand us back an invalid packet number */ + assert(packetnum_valid(packetnum)); p = &s->data[packetnum][0]; /* ??? Multicast packets? */ status = 0; -- 2.47.1