Messages in this thread Patch in this message | | | From | ChenXiaoSong <> | Subject | [PATCH] tty: n_gsm: fix NULL pointer dereference in gsmld_receive_buf() | Date | Thu, 11 Aug 2022 12:28:48 +0800 |
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Syzkaller reported NULL pointer dereference bug as follows:
BUG: kernel NULL pointer dereference, address: 0000000000000000 PGD 0 P4D 0 Oops: 0010 [#1] PREEMPT SMP KASAN PTI CPU: 3 PID: 1360 Comm: a.out Not tainted 5.19.0-next-20220810 #9 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014 RIP: 0010:0x0 Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6. RSP: 0018:ffffc9000570fcf8 EFLAGS: 00010202 RAX: 0000000000000001 RBX: ffff8880189c2000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8880189c2000 RBP: ffffc9000570fda1 R08: 0000000000000000 R09: ffffffff8f59ab27 R10: ffffc9000570fd58 R11: ffff8880196f8000 R12: 0000000000000001 R13: 0000000000000000 R14: ffffc9000570fd90 R15: dffffc0000000000 FS: 00007f382232c540(0000) GS:ffff888107d80000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffffffffffffffd6 CR3: 0000000101452005 CR4: 0000000000770ee0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: <TASK> gsmld_receive_buf+0x1c7/0x320 tty_ioctl+0x50e/0x1520 __x64_sys_ioctl+0x19c/0x210 do_syscall_64+0x38/0x90 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x7f382225e9b9 Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d a7 54 0c 00 f7 d8 64 89 01 48 RSP: 002b:00007ffd1c0fdd98 EFLAGS: 00000217 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f382225e9b9 RDX: 00007ffd1c0fdda4 RSI: 0000000000005412 RDI: 0000000000000004 RBP: 00007ffd1c0fddb0 R08: 000000000000000e R09: 000000001c0fdea0 R10: 0000000000000000 R11: 0000000000000217 R12: 0000560d89007070 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 </TASK> Modules linked in: CR2: 0000000000000000 ---[ end trace 0000000000000000 ]---
Reproducer(c program): 1. int fd = open("/dev/char/4:20", O_RDWR, 0); 2. int arg = 0x15; ioctl(fd, 0x5423, &arg); 3. int arg2 = 0; ioctl(fd, 0x5412, &arg2);
gsm->receive is NULL when gsm_mux is not activated by gsm_activate_mux():
ioctl(fd, 0x5423, &arg) vfs_ioctl tty_ioctl tiocsetd tty_set_ldisc tty_ldisc_open gsmld_open gsm_alloc_mux gsm = kzalloc(sizeof(struct gsm_mux), GFP_KERNEL) gsm->receive == NULL ioctl(fd, 0x5412, &arg2) vfs_ioctl tty_ioctl tiocsti // fake input character gsmld_receive_buf gsm->receive == NULL
Fix this by adding sanity check on struct gsm_mux->receive.
Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com> --- drivers/tty/n_gsm.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index caa5c14ed57f..f1621667b69f 100644 --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -2850,6 +2850,9 @@ static void gsmld_receive_buf(struct tty_struct *tty, const unsigned char *cp, struct gsm_mux *gsm = tty->disc_data; char flags = TTY_NORMAL; + if (!gsm->receive) + return; + if (debug & 4) gsm_hex_dump_bytes(__func__, cp, count); -- 2.31.1
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