HID: magicmouse: prevent unbounded recursion in magicmouse_raw_event()

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magicmouse_raw_event() handles DOUBLE_REPORT_ID (0xf7) packets, which pack
two touch reports into one, by splitting the packet and calling itself on
each half. The only guard against runaway recursion is a "size < 1" check,
which stops zero-sized calls but does not bound the recursion depth.

A malicious HID device that matches this driver can send a report starting
with DOUBLE_REPORT_ID and filled with the sequence [0xf7, 0x00]. Each level
consumes two bytes and recurses on the remainder, so an incoming report of
up to HID_MAX_BUFFER_SIZE (16 KiB) drives roughly 8000 nested calls. That
easily exhausts the 16 KiB kernel stack, leading to a stack overflow: a
panic with CONFIG_VMAP_STACK, or memory corruption without it.

A double report only ever wraps two normal reports; it is never
legitimately nested. Refuse to re-enter the DOUBLE_REPORT_ID case from a
recursive call so the recursion depth is bounded to two, while all valid
packets keep being parsed exactly as before.

Fixes: a462230e16 ("HID: magicmouse: enable Magic Trackpad support")
Link: https://lore.kernel.org/linux-input/20260706181347.700DB1F00A3F@smtp.kernel.org/
Cc: stable@vger.kernel.org
Signed-off-by: Jose Villaseñor Montfort <pepemontfort@gmail.com>
Reviewed-by: Alec Hall <signshop.alec@gmail.com>
Tested-by: Alec Hall <signshop.alec@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

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Jose Villaseñor Montfort 2026-07-14 23:35:26 -06:00 • committed by Jiri Kosina

parent 28a3e326fa

commit db8d634128

1 changed files with 20 additions and 5 deletions

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drivers/hid/hid-magicmouse.c

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