[PATCH] reset: Fix crash when freeing non-existent optional resets

[Geert Uytterhoeven]

When obtaining one or more optional resets, non-existent resets are
stored as NULL pointers, and all related error and cleanup paths need to
take this into account.

Currently only reset_control_put() and reset_control_bulk_put()
get this right.  All of __reset_control_bulk_get(),
of_reset_control_array_get(), and reset_control_array_put() lack the
proper checking, causing NULL pointer dereferences on failure or
release.

Fix this by moving the existing check from reset_control_bulk_put() to
__reset_control_put_internal(), so it applies to all callers.
The double check in reset_control_put() doesn't hurt.

Fixes: 17c82e206d2a3cd8 ("reset: Add APIs to manage array of resets")
Fixes: 48d71395896d54ee ("reset: Add reset_control_bulk API")
Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
---
Crash seen on the Renesas R-Car S4-based Spider development board, using
a (buggy) out-of-tree patch[1].  As the (mutually-exclusive) PCIe host and
endpoint nodes share the same reset,
devm_reset_control_bulk_get_optional_exclusive() fails, and crashes in
the error path:

    /soc/pcie@e65d0000 requests exclusive control over reset pwr shared with /soc/pcie-ep@e65d0000 on /soc/clock-controller@e6150000
    Unable to handle kernel NULL pointer dereference at virtual address 000000000000001c
    Mem abort info:
      ESR = 0x0000000096000005
      EC = 0x25: DABT (current EL), IL = 32 bits
      SET = 0, FnV = 0
      EA = 0, S1PTW = 0
      FSC = 0x05: level 1 translation fault
    Data abort info:
      ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
      CM = 0, WnR = 0, TnD = 0, TagAccess = 0
      GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
    user pgtable: 4k pages, 39-bit VAs, pgdp=00000004810b4000
    [000000000000001c] pgd=0000000000000000, p4d=0000000000000000, pud=0000000000000000
    Internal error: Oops: 0000000096000005 [#1] SMP
    pstate: 00400005 (nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
    pc : __reset_control_put_internal+0x90/0xc8
    lr : __reset_control_bulk_get+0xd4/0xd8
    sp : ffffffc08174ba20
    x29: ffffffc08174ba20 x28: ffffff8440010cd0 x27: ffffff8440a6f8c0
    x26: 0000000000000001 x25: 0000000000000001 x24: 0000000000000000
    x23: ffffff84409d4410 x22: ffffff8440a6fe48 x21: ffffffc080e8fae0
    x20: 0000000000000005 x19: 0000000000000000 x18: 0000000000000000
    x17: 6168732072777020 x16: 7465736572207265 x15: 766f206c6f72746e
    x14: 6f63206576697375 x13: 3030303035313665 x12: 4072656c6c6f7274
    x11: 6e6f632d6b636f6c x10: 632f636f732f206e x9 : 6c63786520737473
    x8 : 6575716572203030 x7 : 205d383432323136 x6 : ffffffc080e8fae0
    x5 : ffffffc080e8fae0 x4 : 0000000000000004 x3 : 0000000000000000
    x2 : 000000000000001c x1 : 00000000ffffffff x0 : 000000000000001c
    Call trace:
     __reset_control_put_internal+0x90/0xc8
     __reset_control_bulk_get+0xd4/0xd8
     __devm_reset_control_bulk_get+0x78/0xcc
     dw_pcie_get_resources+0x2e8/0x344
     dw_pcie_host_init+0x64/0x538
     rcar_gen4_pcie_probe+0x1a8/0x1ec
     platform_probe+0x68/0xb8
     really_probe+0x140/0x278
     __driver_probe_device+0xf4/0x10c
     driver_probe_device+0x50/0x100
     __device_attach_driver+0xb0/0xd0
     bus_for_each_drv+0xa8/0xd0
     __device_attach_async_helper+0x70/0xc4
     async_run_entry_fn+0x38/0x108
     process_scheduled_works+0x1c4/0x270
     worker_thread+0x1fc/0x26c
     kthread+0xbc/0xcc
     ret_from_fork+0x10/0x20
    Code: 97f88daf 14000009 91007262 12800001 (b8610041)
    ---[ end trace 0000000000000000 ]---

[1] "[PATCH v3] reset: Exclusive resets must be dedicated to a single
     hardware block"
    https://lore.kernel.org/r/20181113133520.20889-1-geert+renesas@xxxxxxxxx
---
 drivers/reset/core.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/reset/core.c b/drivers/reset/core.c
index 7ece6a8e9858555d..4d5a78d3c085bc76 100644
--- a/drivers/reset/core.c
+++ b/drivers/reset/core.c
@@ -807,6 +807,9 @@ static void __reset_control_put_internal(struct reset_control *rstc)
 {
 	lockdep_assert_held(&reset_list_mutex);
 
+	if (IS_ERR_OR_NULL(rstc))
+		return;
+
 	kref_put(&rstc->refcnt, __reset_control_release);
 }
 
@@ -1017,11 +1020,8 @@ EXPORT_SYMBOL_GPL(reset_control_put);
 void reset_control_bulk_put(int num_rstcs, struct reset_control_bulk_data *rstcs)
 {
 	mutex_lock(&reset_list_mutex);
-	while (num_rstcs--) {
-		if (IS_ERR_OR_NULL(rstcs[num_rstcs].rstc))
-			continue;
+	while (num_rstcs--)
 		__reset_control_put_internal(rstcs[num_rstcs].rstc);
-	}
 	mutex_unlock(&reset_list_mutex);
 }
 EXPORT_SYMBOL_GPL(reset_control_bulk_put);
-- 
2.34.1