linux-kernel - [PATCH] tty: serial: jsm: add checks against NULL pointer dereference

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Message-Id: <1622702480-32140-1-git-send-email-zheyuma97@gmail.com>
Date:   Thu,  3 Jun 2021 06:41:20 +0000
From:   Zheyu Ma <zheyuma97@...il.com>
To:     gregkh@...uxfoundation.org, jirislaby@...nel.org
Cc:     zheyuma97@...il.com, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] tty: serial: jsm: add checks against NULL pointer dereference

In function 'neo_intr', the driver uses 'ch->ch_equeue' and
'ch->ch_reuque'. These two pointers are initialized in 'jsm_tty_open',
but the interrupt handler 'neo_intr' has been registered in the probe
progress. If 'jsm_tty_open' has not been called at this time, it will
cause null pointer dereference.

Once the driver registers the interrupt handler, the driver should be
ready to handle it.

Fix this by checking whether it is a null pointer.

This log reveals it:

[   50.934983] BUG: kernel NULL pointer dereference, address:
0000000000000000
[   50.938297] #PF: supervisor write access in kernel mode
[   50.940075] #PF: error_code(0x0002) - not-present page
[   50.940460] PGD 0 P4D 0
[   50.940654] Oops: 0002 [#1] PREEMPT SMP PTI
[   50.940967] CPU: 2 PID: 0 Comm: swapper/2 Not tainted
5.12.4-g70e7f0549188-dirty #97
[   50.941554] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
[   50.942419] RIP: 0010:memcpy_fromio+0x75/0xa0
[   50.942759] Code: e9 02 f3 a5 41 f6 c5 02 74 02 66 a5 41 f6 c5 01 74
01 a4 e8 5d 93 6b ff 5b 41 5c 41 5d 5d c3 e8 51 93 6b ff 4c 89 e7 48 89
de <a4> 49 89 fc 48 89 f3 49 83 ed 01 eb a4 e8 39 93 6b ff 4c 89 e7 48
[   50.944158] RSP: 0018:ffffc90000118df8 EFLAGS: 00010046
[   50.944559] RAX: ffff888100258000 RBX: ffffc90007f0030f
RCX: 0000000000000000
[   50.945114] RDX: 0000000000000000 RSI: ffffc90007f0030f
RDI: 0000000000000000
[   50.945652] RBP: ffffc90000118e10 R08: 0000000000000000
R09: 0000000000000000
[   50.946192] R10: 0000000000000000 R11: 0000000000000001
R12: 0000000000000000
[   50.946729] R13: 0000000000000001 R14: 0000000007f0021e
R15: 0000000000000000
[   50.947279] FS:  0000000000000000(0000) GS:ffff88817bc80000(0000)
knlGS:0000000000000000
[   50.947912] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   50.948346] CR2: 0000000000000000 CR3: 0000000107950000
CR4: 00000000000006e0
[   50.948892] DR0: 0000000000000000 DR1: 0000000000000000
DR2: 0000000000000000
[   50.949429] DR3: 0000000000000000 DR6: 00000000fffe0ff0
DR7: 0000000000000400
[   50.949950] Call Trace:
[   50.950138]  <IRQ>
[   50.950292]  neo_copy_data_from_uart_to_queue+0x2f7/0x4e0
[   50.950694]  neo_intr+0x253/0x7a0
[   50.950975]  __handle_irq_event_percpu+0x53/0x3e0
[   50.951352]  handle_irq_event_percpu+0x35/0x90
[   50.951706]  handle_irq_event+0x39/0x60
[   50.951999]  handle_fasteoi_irq+0xc2/0x1d0
[   50.952319]  __common_interrupt+0x7f/0x150
[   50.952638]  common_interrupt+0xb4/0xd0
[   50.952954]  </IRQ>
[   50.953136]  asm_common_interrupt+0x1e/0x40
[   50.969513] Kernel panic - not syncing: Fatal exception in interrupt
[   50.970151] Dumping ftrace buffer:
[   50.970420]    (ftrace buffer empty)
[   50.970693] Kernel Offset: disabled
[   50.970968] Rebooting in 1 seconds..

Signed-off-by: Zheyu Ma <zheyuma97@...il.com>
---
 drivers/tty/serial/jsm/jsm_neo.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/jsm/jsm_neo.c b/drivers/tty/serial/jsm/jsm_neo.c
index bf0e2a4cb0ce..46be0b53ab42 100644
--- a/drivers/tty/serial/jsm/jsm_neo.c
+++ b/drivers/tty/serial/jsm/jsm_neo.c
@@ -716,7 +716,7 @@ static void neo_parse_isr(struct jsm_board *brd, u32 port)
 		return;
 
 	ch = brd->channels[port];
-	if (!ch)
+	if (!ch || !ch->ch_equeue || !ch->ch_rqueue)
 		return;
 
 	/* Here we try to figure out what caused the interrupt to happen */
@@ -832,7 +832,7 @@ static inline void neo_parse_lsr(struct jsm_board *brd, u32 port)
 		return;
 
 	ch = brd->channels[port];
-	if (!ch)
+	if (!ch || !ch->ch_equeue || !ch->ch_rqueue)
 		return;
 
 	linestatus = readb(&ch->ch_neo_uart->lsr);
@@ -1172,7 +1172,7 @@ static irqreturn_t neo_intr(int irq, void *voidbrd)
 				continue;
 
 			ch = brd->channels[port];
-			if (!ch)
+			if (!ch || !ch->ch_equeue || !ch->ch_rqueue)
 				continue;
 
 			neo_copy_data_from_uart_to_queue(ch);
-- 
2.17.6