Messages in this thread | | | Date | Thu, 18 May 2023 10:37:05 +0800 | Subject | Re: [PATCH v6] kobject: Fix global-out-of-bounds in kobject_action_type() | From | Xia Fukun <> |
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On 2023/5/17 20:17, Greg KH wrote: > On Wed, May 17, 2023 at 06:19:57PM +0800, Xia Fukun wrote: >> --- a/include/linux/kobject.h >> +++ b/include/linux/kobject.h >> @@ -32,6 +32,9 @@ >> #define UEVENT_NUM_ENVP 64 /* number of env pointers */ >> #define UEVENT_BUFFER_SIZE 2048 /* buffer for the variables */ >> >> +/* the maximum length of the string contained in kobject_actions[] */ >> +#define UEVENT_KACT_STRSIZE 16 > > Why does this value need to be in a global .h file when it is only used > in one .c file? > > And how are you going to keep it in sync with kobject_actions if it > changes in the future? And that variable isn't even in this file, how > would anyone know to modify this if the structure changes in a .c file?
Your criticism is correct. UEVENT_KACT_STRSIZE should not be defined in the global .h file here. I will move it to that .c file.
>> --- a/lib/kobject_uevent.c >> +++ b/lib/kobject_uevent.c >> @@ -66,7 +66,8 @@ static int kobject_action_type(const char *buf, size_t count, >> enum kobject_action action; >> size_t count_first; >> const char *args_start; >> - int ret = -EINVAL; >> + int i, ret = -EINVAL; >> + char kobj_act_buf[UEVENT_KACT_STRSIZE] = ""; > > Why does this need to be initialized?
My initialization method has some flaws, which should be done as follows:
char kobj_act_buf[UEVENT_KACT_STRSIZE] = {0};
Initialize the string kobj_act_buf to "/0" and parse it using sysfs_match_string after subsequent copy operations.
> And are you sure the size is correct? If so, how?
UEVENT_KACT_STRSIZE is defined as the maximum length of the string contained in kobject_actions[].
At present, the maximum length of strings in this array is 7. Based on the actual meaning of these strings, these actions will not exceed 16 if there are any subsequent changes.
> And how was any of this tested? Based on your prior submissions, we are > going to require some sort of proof. What would you do if you were in > my position?
My testing method is to apply the patch, compile the kernel image, and start the QEMU virtual machine. Then compile and execute the code mentioned in the patch that triggers out-of-bounds issues.
In addition, the following operations will be performed to verify the functions mentioned by Peter Rajnoha <prajnoha@redhat.com>:
# echo "add fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed A=1 B=abc" > /sys/block/ram0/uevent
# udevadm monitor --kernel --env monitor will print the received events for: KERNEL - the kernel uevent
KERNEL[189.376386] add /devices/virtual/block/ram0 (block) ACTION=add DEVPATH=/devices/virtual/block/ram0 SUBSYSTEM=block SYNTH_UUID=fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed SYNTH_ARG_A=1 SYNTH_ARG_B=abc DEVNAME=/dev/ram0 DEVTYPE=disk DISKSEQ=14 SEQNUM=3781 MAJOR=1 MINOR=0
> thanks, > > greg k-h
Thank you for your suggestion. My submission was indeed negligent, and your guidance has benefited me greatly.
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