5.4-stable review patch. If anyone has any objections, please let me know.
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From: Forest Crossman cyrozap@gmail.com
[ Upstream commit 368ed48a5ef52e384f54d5809f0a0b79ac567479 ]
The usbmon binary interface currently truncates captures of large transfers from higher-speed USB devices. Because a single event capture is limited to one-fifth of the total buffer size, the current maximum size of a captured URB is around 240 KiB. This is insufficient when capturing traffic from modern devices that use transfers of several hundred kilobytes or more, as truncated URBs can make it impossible for user-space USB analysis tools like Wireshark to properly defragment and reassemble higher-level protocol packets in the captured data.
The root cause of this issue is the 1200 KiB BUFF_MAX limit, which has not been changed since the binary interface was introduced in 2006.
To resolve this issue, this patch increases BUFF_MAX to 64 MiB. The original comment for BUFF_MAX based the limit's calculation on a saturated 480 Mbit/s bus. Applying the same logic to a modern USB 3.2 Gen 2×2 20 Gbit/s bus (~2500 MB/s over a 20ms window) indicates the buffer should be at least 50 MB. The new limit of 64 MiB covers that, plus a little extra for any overhead.
With this change, both users and developers should now be able to debug and reverse engineer modern USB devices even when running unmodified distro kernels.
Please note that this change does not affect the default buffer size. A larger buffer is only allocated when a user explicitly requests it via the MON_IOCT_RING_SIZE ioctl, so the change to the maximum buffer size should not unduly increase memory usage for users that don't deliberately request a larger buffer.
Link: https://lore.kernel.org/CAO3ALPzdUkmMr0YMrODLeDSLZqNCkWcAP8NumuPHLjNJ8wC1kQ@... Signed-off-by: Forest Crossman cyrozap@gmail.com Acked-by: Alan Stern stern@rowland.harvard.edu Link: https://lore.kernel.org/r/CAO3ALPxU5RzcoueC454L=WZ1qGMfAcnxm+T+p+9D8O9mcrUbC... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/usb/mon/mon_bin.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/drivers/usb/mon/mon_bin.c b/drivers/usb/mon/mon_bin.c index 35483217b1f6c..93998d328d9aa 100644 --- a/drivers/usb/mon/mon_bin.c +++ b/drivers/usb/mon/mon_bin.c @@ -68,18 +68,20 @@ * The magic limit was calculated so that it allows the monitoring * application to pick data once in two ticks. This way, another application, * which presumably drives the bus, gets to hog CPU, yet we collect our data. - * If HZ is 100, a 480 mbit/s bus drives 614 KB every jiffy. USB has an - * enormous overhead built into the bus protocol, so we need about 1000 KB. + * + * Originally, for a 480 Mbit/s bus this required a buffer of about 1 MB. For + * modern 20 Gbps buses, this value increases to over 50 MB. The maximum + * buffer size is set to 64 MiB to accommodate this. * * This is still too much for most cases, where we just snoop a few * descriptor fetches for enumeration. So, the default is a "reasonable" - * amount for systems with HZ=250 and incomplete bus saturation. + * amount for typical, low-throughput use cases. * * XXX What about multi-megabyte URBs which take minutes to transfer? */ -#define BUFF_MAX CHUNK_ALIGN(1200*1024) -#define BUFF_DFL CHUNK_ALIGN(300*1024) -#define BUFF_MIN CHUNK_ALIGN(8*1024) +#define BUFF_MAX CHUNK_ALIGN(64*1024*1024) +#define BUFF_DFL CHUNK_ALIGN(300*1024) +#define BUFF_MIN CHUNK_ALIGN(8*1024)
/* * The per-event API header (2 per URB).