In the Linux kernel, the following vulnerability has been resolved:

uprobe: avoid out-of-bounds memory access of fetching args

Uprobe needs to fetch args into a percpu buffer, and then copy to ring buffer to avoid non-atomic context problem.

Sometimes user-space strings, arrays can be very large, but the size of percpu buffer is only page size. And storetraceargs() won't check whether these data exceeds a single page or not, caused out-of-bounds memory access.

It could be reproduced by following steps: 1. build kernel with CONFIG_KASAN enabled 2. save follow program as test.c

\#include <stdio.h>
\#include <stdlib.h>
\#include <string.h>

// If string length large than MAX_STRING_SIZE, the fetch_store_strlen()
// will return 0, cause __get_data_size() return shorter size, and
// store_trace_args() will not trigger out-of-bounds access.
// So make string length less than 4096.
\#define STRLEN 4093

void generate_string(char *str, int n)
{
    int i;
    for (i = 0; i < n; ++i)
    {
        char c = i % 26 + 'a';
        str[i] = c;
    }
    str[n-1] = '\0';
}

void print_string(char *str)
{
    printf("%s\n", str);
}

int main()
{
    char tmp[STRLEN];

    generate_string(tmp, STRLEN);
    print_string(tmp);

    return 0;
}

3. compile program gcc -o test test.c

4. get the offset of print_string()

   objdump -t test | grep -w print_string
   0000000000401199 g     F .text  000000000000001b              print_string
   

5. configure uprobe with offset 0x1199

   off=0x1199
   
   cd /sys/kernel/debug/tracing/
   echo "p /root/test:${off} arg1=+0(%di):ustring arg2=\$comm arg3=+0(%di):ustring"
    > uprobe_events
   echo 1 > events/uprobes/enable
   echo 1 > tracing_on
   

6. run test, and kasan will report error.

BUG: KASAN: use-after-free in strncpyfromuser+0x1d6/0x1f0 Write of size 8 at addr ffff88812311c004 by task test/499CPU: 0 UID: 0 PID: 499 Comm: test Not tainted 6.12.0-rc3+ #18 Hardware name: Red Hat KVM, BIOS 1.16.0-4.al8 04/01/2014 Call Trace: <TASK> dumpstacklvl+0x55/0x70 printaddressdescription.constprop.0+0x27/0x310 kasanreport+0x10f/0x120 ? strncpyfromuser+0x1d6/0x1f0 strncpyfromuser+0x1d6/0x1f0 ? rmqueue.constprop.0+0x70d/0x2ad0 processfetchinsn+0xb26/0x1470 ? pfxprocessfetchinsn+0x10/0x10 ? rawspinlock+0x85/0xe0 ? _pfxrawspinlock+0x10/0x10 ? pteoffsetmap+0x1f/0x2d0 ? unwindnextframe+0xc5f/0x1f80 ? archstackwalk+0x68/0xf0 ? isbpftextaddress+0x23/0x30 ? kerneltextaddress.part.0+0xbb/0xd0 ? _kerneltextaddress+0x66/0xb0 ? unwindgetreturnaddress+0x5e/0xa0 ? _pfxstacktraceconsumeentry+0x10/0x10 ? archstackwalk+0xa2/0xf0 ? rawspinlockirqsave+0x8b/0xf0 ? _pfxrawspinlockirqsave+0x10/0x10 ? depotallocstack+0x4c/0x1f0 ? rawspinunlockirqrestore+0xe/0x30 ? stackdepotsaveflags+0x35d/0x4f0 ? kasansavestack+0x34/0x50 ? kasansavestack+0x24/0x50 ? mutexlock+0x91/0xe0 ? _pfxmutexlock+0x10/0x10 prepareuprobebuffer.part.0+0x2cd/0x500 uprobedispatcher+0x2c3/0x6a0 ? _pfxuprobedispatcher+0x10/0x10 ? _kasanslaballoc+0x4d/0x90 handlerchain+0xdd/0x3e0 handleswbp+0x26e/0x3d0 ? _pfxhandleswbp+0x10/0x10 ? uprobepresstepnotifier+0x151/0x1b0 irqentryexittousermode+0xe2/0x1b0 asmexcint3+0x39/0x40 RIP: 0033:0x401199 Code: 01 c2 0f b6 45 fb 88 02 83 45 fc 01 8b 45 fc 3b 45 e4 7c b7 8b 45 e4 48 98 48 8d 50 ff 48 8b 45 e8 48 01 d0 ce RSP: 002b:00007ffdf00576a8 EFLAGS: 00000206 RAX: 00007ffdf00576b0 RBX: 0000000000000000 RCX: 0000000000000ff2 RDX: 0000000000000ffc RSI: 0000000000000ffd RDI: 00007ffdf00576b0 RBP: 00007ffdf00586b0 R08: 00007feb2f9c0d20 R09: 00007feb2f9c0d20 R10: 0000000000000001 R11: 0000000000000202 R12: 0000000000401040 R13: 00007ffdf0058780 R14: 0000000000000000 R15: 0000000000000000 </TASK>

This commit enforces the buffer's maxlen less than a page-size to avoid storetraceargs() out-of-memory access.