ping

On 2020/12/24 15:42, Xiaoming Ni wrote:
The process_sysctl_arg() does not check whether val is empty before
  invoking strlen(val). If the command line parameter () is incorrectly
  configured and val is empty, oops is triggered.

For example, "hung_task_panic=1" is incorrectly written as "hung_task_panic".

log:
        Kernel command line: .... hung_task_panic
        ....
        [000000000000000n] user address but active_mm is swapper
        Internal error: Oops: 96000005 [#1] SMP
        Modules linked in:
        CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.10.1 #1
        Hardware name: linux,dummy-virt (DT)
        pstate: 40000005 (nZcv daif -PAN -UAO -TCO BTYPE=--)
        pc : __pi_strlen+0x10/0x98
        lr : process_sysctl_arg+0x1e4/0x2ac
        sp : ffffffc01104bd40
        x29: ffffffc01104bd40 x28: 0000000000000000
        x27: ffffff80c0a4691e x26: ffffffc0102a7c8c
        x25: 0000000000000000 x24: ffffffc01104be80
        x23: ffffff80c22f0b00 x22: ffffff80c02e28c0
        x21: ffffffc0109f9000 x20: 0000000000000000
        x19: ffffffc0107c08de x18: 0000000000000003
        x17: ffffffc01105d000 x16: 0000000000000054
        x15: ffffffffffffffff x14: 3030253078413830
        x13: 000000000000ffff x12: 0000000000000000
        x11: 0101010101010101 x10: 0000000000000005
        x9 : 0000000000000003 x8 : ffffff80c0980c08
        x7 : 0000000000000000 x6 : 0000000000000002
        x5 : ffffff80c0235000 x4 : ffffff810f7c7ee0
        x3 : 000000000000043a x2 : 00bdcc4ebacf1a54
        x1 : 0000000000000000 x0 : 0000000000000000
        Call trace:
         __pi_strlen+0x10/0x98
         parse_args+0x278/0x344
         do_sysctl_args+0x8c/0xfc
         kernel_init+0x5c/0xf4
         ret_from_fork+0x10/0x30
        Code: b200c3eb 927cec01 f2400c07 54000301 (a8c10c22)

Fixes: 3db978d480e2843 ("kernel/sysctl: support setting sysctl parameters
  from kernel command line")
Signed-off-by: Xiaoming Ni <nixiaom...@huawei.com>
---
  fs/proc/proc_sysctl.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 317899222d7f..4516411a2b44 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -1757,6 +1757,9 @@ static int process_sysctl_arg(char *param, char *val,
        loff_t pos = 0;
        ssize_t wret;
+ if (!val)
+               return 0;
+
        if (strncmp(param, "sysctl", sizeof("sysctl") - 1) == 0) {
                param += sizeof("sysctl") - 1;

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