clk: renesas: rzv2h: Fix use-after-free in MSTOP refcount handling

Avoid triggering a `refcount_t: addition on 0; use-after-free.` warning
when registering a module clock with the same MSTOP configuration. The
issue arises when a module clock is registered but not enabled, resulting
in a `ref_cnt` of 0. Subsequent calls to `refcount_inc()` on such clocks
cause the kernel to warn about use-after-free.

[ 0.113529] ------------[ cut here ]------------
[ 0.113537] refcount_t: addition on 0; use-after-free.
[ 0.113576] WARNING: CPU: 2 PID: 1 at lib/refcount.c:25 refcount_warn_saturate+0x120/0x144
[ 0.113602] Modules linked in:
[ 0.113616] CPU: 2 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.13.0-rc3+ torvalds#446
[ 0.113629] Hardware name: Renesas RZ/V2H EVK Board based on r9a09g057h44 (DT)
[ 0.113641] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 0.113652] pc : refcount_warn_saturate+0x120/0x144
[ 0.113664] lr : refcount_warn_saturate+0x120/0x144
[ 0.113675] sp : ffff8000818aba90
[ 0.113682] x29: ffff8000818aba90 x28: ffff0000c0d96450 x27: ffff0000c0d96440
[ 0.113699] x26: 0000000000000014 x25: 0000000000051000 x24: ffff0000c0ad6480
[ 0.113714] x23: ffff0000c0d96200 x22: ffff800080fae558 x21: 00000000000001e0
[ 0.113730] x20: ffff0000c0b11c10 x19: ffff8000815ae6f0 x18: 0000000000000006
[ 0.113745] x17: ffff800081765368 x16: 0000000000000000 x15: 0765076507720766
[ 0.113760] x14: ffff8000816a3ea0 x13: 0765076507720766 x12: 072d077207650774
[ 0.113776] x11: ffff8000816a3ea0 x10: 00000000000000ce x9 : ffff8000816fbea0
[ 0.113791] x8 : 0000000000017fe8 x7 : 00000000fffff000 x6 : ffff8000816fbea0
[ 0.113806] x5 : 80000000fffff000 x4 : 0000000000000000 x3 : 0000000000000000
[ 0.113821] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff0000c0158000
[ 0.113837] Call trace:
[ 0.113845]  refcount_warn_saturate+0x120/0x144 (P)
[ 0.113859]  rzv2h_cpg_probe+0x7f8/0xa38
[ 0.113874]  platform_probe+0x68/0xdc
[ 0.113890]  really_probe+0xbc/0x2c0
[ 0.113901]  __driver_probe_device+0x78/0x120
[ 0.113912]  driver_probe_device+0x3c/0x154
[ 0.113923]  __driver_attach+0x90/0x1a0
[ 0.113933]  bus_for_each_dev+0x7c/0xe0
[ 0.113944]  driver_attach+0x24/0x30
[ 0.113954]  bus_add_driver+0xe4/0x208
[ 0.113965]  driver_register+0x68/0x124
[ 0.113975]  __platform_driver_probe+0x54/0xd4
[ 0.113987]  rzv2h_cpg_init+0x24/0x30
[ 0.113998]  do_one_initcall+0x60/0x1d4
[ 0.114013]  kernel_init_freeable+0x214/0x278
[ 0.114028]  kernel_init+0x20/0x140
[ 0.114041]  ret_from_fork+0x10/0x20
[ 0.114052] ---[ end trace 0000000000000000 ]---

Resolve this by checking the `ref_cnt` value before calling
`refcount_inc()`. If `ref_cnt` is 0, reset it to 1 using `refcount_set()`.

Fixes: 7bd4cb3 ("clk: renesas: rzv2h: Add MSTOP support")
Signed-off-by: Lad Prabhakar <[email protected]>
Reviewed-by: Geert Uytterhoeven <[email protected]>
Fixes: 7bd4cb3 ("clk: renesas: rzv2h: Add MSTOP support")
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Geert Uytterhoeven <[email protected]>

Author: prabhakarlad

drivers/clk/renesas/rzv2h-cpg.c

@@ -565,8 +565,12 @@ static struct rzv2h_mstop
 			continue;
 
 		if (BUS_MSTOP(clk->mstop->idx, clk->mstop->mask) == mstop_data) {
-			if (rzv2h_mod_clock_is_enabled(&clock->hw))
-				refcount_inc(&clk->mstop->ref_cnt);
+			if (rzv2h_mod_clock_is_enabled(&clock->hw)) {
+				if (refcount_read(&clk->mstop->ref_cnt))
+					refcount_inc(&clk->mstop->ref_cnt);
+				else
+					refcount_set(&clk->mstop->ref_cnt, 1);
+			}
 			return clk->mstop;
 		}
 	}