Vulnerability CVE-2024-35825

Vulnerability CVE-2024-35825

Published: 2024-05-17

Description:

In the Linux kernel, the following vulnerability has been resolved:

usb: gadget: ncm: Fix handling of zero block length packets

While connecting to a Linux host with CDC_NCM_NTB_DEF_SIZE_TX
set to 65536, it has been observed that we receive short packets,
which come at interval of 5-10 seconds sometimes and have block
length zero but still contain 1-2 valid datagrams present.

According to the NCM spec:

"If wBlockLength = 0x0000, the block is terminated by a
short packet. In this case, the USB transfer must still
be shorter than dwNtbInMaxSize or dwNtbOutMaxSize. If
exactly dwNtbInMaxSize or dwNtbOutMaxSize bytes are sent,
and the size is a multiple of wMaxPacketSize for the
given pipe, then no ZLP shall be sent.

wBlockLength= 0x0000 must be used with extreme care, because
of the possibility that the host and device may get out of
sync, and because of test issues.

wBlockLength = 0x0000 allows the sender to reduce latency by
starting to send a very large NTB, and then shortening it when
the sender discovers that there??s not sufficient data to justify
sending a large NTB"

However, there is a potential issue with the current implementation,
as it checks for the occurrence of multiple NTBs in a single
giveback by verifying if the leftover bytes to be processed is zero
or not. If the block length reads zero, we would process the same
NTB infintely because the leftover bytes is never zero and it leads
to a crash. Fix this by bailing out if block length reads zero.

References:

https://git.kernel.org/stable/c/e2dbfea520e60d58e0c498ba41bde10452257779

https://git.kernel.org/stable/c/a766761d206e7c36d7526e0ae749949d17ca582c

https://git.kernel.org/stable/c/ef846cdbd100f7f9dc045e8bcd7fe4b3a3713c03

https://git.kernel.org/stable/c/92b051b87658df7649ffcdef522593f21a2b296b

https://git.kernel.org/stable/c/7664ee8bd80309b90d53488b619764f0a057f2b7

https://git.kernel.org/stable/c/a0f77b5d6067285b8eca0ee3bd1e448a6258026f

https://git.kernel.org/stable/c/6b2c73111a252263807b7598682663dc33aa4b4c

https://git.kernel.org/stable/c/f90ce1e04cbcc76639d6cba0fdbd820cd80b3c70

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