CVE-2026-90386 — i3c: dw: avoid shift-out-of-bounds when DAA assigns no devices

Affected: Linux

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

i3c: dw: avoid shift-out-of-bounds when DAA assigns no devices

On an empty bus ENTDAA assigns nothing, so cmd->rx_len (the count of addresses left unassigned) equals master->maxdevs.

The GENMASK() index master->maxdevs - cmd->rx_len - 1 then becomes -1, which trips up UBSAN. This happens every time on boot on a Gigabyte/AMD server:

UBSAN: shift-out-of-bounds in drivers/i3c/master/dw-i3c-master.c:905:12 shift exponent 64 is too large for 64-bit type 'long unsigned int' CPU: 7 UID: 0 PID: 963 Comm: (udev-worker) Not tainted 7.0.11-200.fc44.x86_64 #1 PREEMPT(lazy) Hardware name: Giga Computing E163-Z34-AAH1-000/MZ33-DC1-000, BIOS R32_F45 04/01/2026 Call Trace: <TASK> dump_stack_lvl+0x5d/0x80 ubsan_epilogue+0x5/0x2b __ubsan_handle_shift_out_of_bounds.cold+0xd7/0x1ab dw_i3c_master_daa.cold+0x1b/0x96 [dw_i3c_master] i3c_master_do_daa_ext.part.0+0x3e/0xf0 [i3c]

Skip the mask when no new device was assigned.

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CVE-2026-90386 — i3c: dw: avoid shift-out-of-bounds when DAA assigns no devices