[PATCH] tty: check name length in tty_find_polling_driver()
From: miles.chen
Date: Sun Oct 07 2018 - 22:39:34 EST
From: Miles Chen <miles.chen@xxxxxxxxxxxx>
The issue is found by a fuzzing test.
If tty_find_polling_driver() recevies an incorrect input such as
',,' or '0b', the len becomes 0 and strncmp() always return 0.
In this case, a null p->ops->poll_init() is called and it causes a kernel
panic.
Fix this by checking name length against zero in tty_find_polling_driver().
$echo ,, > /sys/module/kgdboc/parameters/kgdboc
[ 20.804451] WARNING: CPU: 1 PID: 104 at drivers/tty/serial/serial_core.c:457
uart_get_baud_rate+0xe8/0x190
[ 20.804917] Modules linked in:
[ 20.805317] CPU: 1 PID: 104 Comm: sh Not tainted 4.19.0-rc7ajb #8
[ 20.805469] Hardware name: linux,dummy-virt (DT)
[ 20.805732] pstate: 20000005 (nzCv daif -PAN -UAO)
[ 20.805895] pc : uart_get_baud_rate+0xe8/0x190
[ 20.806042] lr : uart_get_baud_rate+0xc0/0x190
[ 20.806476] sp : ffffffc06acff940
[ 20.806676] x29: ffffffc06acff940 x28: 0000000000002580
[ 20.806977] x27: 0000000000009600 x26: 0000000000009600
[ 20.807231] x25: ffffffc06acffad0 x24: 00000000ffffeff0
[ 20.807576] x23: 0000000000000001 x22: 0000000000000000
[ 20.807807] x21: 0000000000000001 x20: 0000000000000000
[ 20.808049] x19: ffffffc06acffac8 x18: 0000000000000000
[ 20.808277] x17: 0000000000000000 x16: 0000000000000000
[ 20.808520] x15: ffffffffffffffff x14: ffffffff00000000
[ 20.808757] x13: ffffffffffffffff x12: 0000000000000001
[ 20.809011] x11: 0101010101010101 x10: ffffff880d59ff5f
[ 20.809292] x9 : ffffff880d59ff5e x8 : ffffffc06acffaf3
[ 20.809549] x7 : 0000000000000000 x6 : ffffff880d59ff5f
[ 20.809803] x5 : 0000000080008001 x4 : 0000000000000003
[ 20.810056] x3 : ffffff900853e6b4 x2 : dfffff9000000000
[ 20.810693] x1 : ffffffc06acffad0 x0 : 0000000000000cb0
[ 20.811005] Call trace:
[ 20.811214] uart_get_baud_rate+0xe8/0x190
[ 20.811479] serial8250_do_set_termios+0xe0/0x6f4
[ 20.811719] serial8250_set_termios+0x48/0x54
[ 20.811928] uart_set_options+0x138/0x1bc
[ 20.812129] uart_poll_init+0x114/0x16c
[ 20.812330] tty_find_polling_driver+0x158/0x200
[ 20.812545] configure_kgdboc+0xbc/0x1bc
[ 20.812745] param_set_kgdboc_var+0xb8/0x150
[ 20.812960] param_attr_store+0xbc/0x150
[ 20.813160] module_attr_store+0x40/0x58
[ 20.813364] sysfs_kf_write+0x8c/0xa8
[ 20.813563] kernfs_fop_write+0x154/0x290
[ 20.813764] vfs_write+0xf0/0x278
[ 20.813951] __arm64_sys_write+0x84/0xf4
[ 20.814400] el0_svc_common+0xf4/0x1dc
[ 20.814616] el0_svc_handler+0x98/0xbc
[ 20.814804] el0_svc+0x8/0xc
[ 20.822005] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
[ 20.826913] Mem abort info:
[ 20.827103] ESR = 0x84000006
[ 20.827352] Exception class = IABT (current EL), IL = 16 bits
[ 20.827655] SET = 0, FnV = 0
[ 20.827855] EA = 0, S1PTW = 0
[ 20.828135] user pgtable: 4k pages, 39-bit VAs, pgdp = (____ptrval____)
[ 20.828484] [0000000000000000] pgd=00000000aadee003, pud=00000000aadee003, pmd=0000000000000000
[ 20.829195] Internal error: Oops: 84000006 [#1] SMP
[ 20.829564] Modules linked in:
[ 20.829890] CPU: 1 PID: 104 Comm: sh Tainted: G W 4.19.0-rc7ajb #8
[ 20.830545] Hardware name: linux,dummy-virt (DT)
[ 20.830829] pstate: 60000085 (nZCv daIf -PAN -UAO)
[ 20.831174] pc : (null)
[ 20.831457] lr : serial8250_do_set_termios+0x358/0x6f4
[ 20.831727] sp : ffffffc06acff9b0
[ 20.831936] x29: ffffffc06acff9b0 x28: ffffff9008d7c000
[ 20.832267] x27: ffffff900969e16f x26: 0000000000000000
[ 20.832589] x25: ffffff900969dfb0 x24: 0000000000000000
[ 20.832906] x23: ffffffc06acffad0 x22: ffffff900969e160
[ 20.833232] x21: 0000000000000000 x20: ffffffc06acffac8
[ 20.833559] x19: ffffff900969df90 x18: 0000000000000000
[ 20.833878] x17: 0000000000000000 x16: 0000000000000000
[ 20.834491] x15: ffffffffffffffff x14: ffffffff00000000
[ 20.834821] x13: ffffffffffffffff x12: 0000000000000001
[ 20.835143] x11: 0101010101010101 x10: ffffff880d59ff5f
[ 20.835467] x9 : ffffff880d59ff5e x8 : ffffffc06acffaf3
[ 20.835790] x7 : 0000000000000000 x6 : ffffff880d59ff5f
[ 20.836111] x5 : c06419717c314100 x4 : 0000000000000007
[ 20.836419] x3 : 0000000000000000 x2 : 0000000000000000
[ 20.836732] x1 : 0000000000000001 x0 : ffffff900969df90
[ 20.837100] Process sh (pid: 104, stack limit = 0x(____ptrval____))
[ 20.837396] Call trace:
[ 20.837566] (null)
[ 20.837816] serial8250_set_termios+0x48/0x54
[ 20.838089] uart_set_options+0x138/0x1bc
[ 20.838570] uart_poll_init+0x114/0x16c
[ 20.838834] tty_find_polling_driver+0x158/0x200
[ 20.839119] configure_kgdboc+0xbc/0x1bc
[ 20.839380] param_set_kgdboc_var+0xb8/0x150
[ 20.839658] param_attr_store+0xbc/0x150
[ 20.839920] module_attr_store+0x40/0x58
[ 20.840183] sysfs_kf_write+0x8c/0xa8
[ 20.840183] sysfs_kf_write+0x8c/0xa8
[ 20.840440] kernfs_fop_write+0x154/0x290
[ 20.840702] vfs_write+0xf0/0x278
[ 20.840942] __arm64_sys_write+0x84/0xf4
[ 20.841209] el0_svc_common+0xf4/0x1dc
[ 20.841471] el0_svc_handler+0x98/0xbc
[ 20.841713] el0_svc+0x8/0xc
[ 20.842057] Code: bad PC value
[ 20.842764] ---[ end trace a8835d7de79aaadf ]---
[ 20.843134] Kernel panic - not syncing: Fatal exception
[ 20.843515] SMP: stopping secondary CPUs
[ 20.844289] Kernel Offset: disabled
[ 20.844634] CPU features: 0x0,21806002
[ 20.844857] Memory Limit: none
[ 20.845172] ---[ end Kernel panic - not syncing: Fatal exception ]---
Signed-off-by: Miles Chen <miles.chen@xxxxxxxxxxxx>
---
drivers/tty/tty_io.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 5e5da9a..252eef2 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -408,7 +408,7 @@ struct tty_driver *tty_find_polling_driver(char *name, int *line)
mutex_lock(&tty_mutex);
/* Search through the tty devices to look for a match */
list_for_each_entry(p, &tty_drivers, tty_drivers) {
- if (strncmp(name, p->name, len) != 0)
+ if (!len || strncmp(name, p->name, len) != 0)
continue;
stp = str;
if (*stp == ',')
--
1.9.1