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Thu, 02 Jan 2025 10:18:47 -0800 (PST) From: Prabhakar X-Google-Original-From: Prabhakar To: Geert Uytterhoeven , Michael Turquette , Stephen Boyd Cc: linux-renesas-soc@vger.kernel.org, linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org, Prabhakar , Biju Das , Fabrizio Castro , Lad Prabhakar Subject: [PATCH v3 1/6] clk: renesas: rzv2h: Fix use-after-free in MSTOP refcount handling Date: Thu, 2 Jan 2025 18:18:34 +0000 Message-ID: <20250102181839.352599-2-prabhakar.mahadev-lad.rj@bp.renesas.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250102181839.352599-1-prabhakar.mahadev-lad.rj@bp.renesas.com> References: <20250102181839.352599-1-prabhakar.mahadev-lad.rj@bp.renesas.com> Precedence: bulk X-Mailing-List: linux-clk@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Lad Prabhakar 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+ #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: 7bd4cb3d6b7c ("clk: renesas: rzv2h: Add MSTOP support") Signed-off-by: Lad Prabhakar Reviewed-by: Geert Uytterhoeven --- v2->v3 - Included RB tag from Geert v1->v2 - Updated commit description - Updated fixes tag commit header --- drivers/clk/renesas/rzv2h-cpg.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/drivers/clk/renesas/rzv2h-cpg.c b/drivers/clk/renesas/rzv2h-cpg.c index 668a2880b2d3..23c89b0de38a 100644 --- a/drivers/clk/renesas/rzv2h-cpg.c +++ b/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; } }