Amazon Linux AMI: CVE-2024-50067: Security patch for kernel (ALAS-2025-1957)

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 store_trace_args() 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 strncpy_from_user+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>

dump_stack_lvl+0x55/0x70

print_address_description.constprop.0+0x27/0x310

kasan_report+0x10f/0x120

? strncpy_from_user+0x1d6/0x1f0

strncpy_from_user+0x1d6/0x1f0

? rmqueue.constprop.0+0x70d/0x2ad0

process_fetch_insn+0xb26/0x1470

? __pfx_process_fetch_insn+0x10/0x10

? _raw_spin_lock+0x85/0xe0

? __pfx__raw_spin_lock+0x10/0x10

? __pte_offset_map+0x1f/0x2d0

? unwind_next_frame+0xc5f/0x1f80

? arch_stack_walk+0x68/0xf0

? is_bpf_text_address+0x23/0x30

? kernel_text_address.part.0+0xbb/0xd0

? __kernel_text_address+0x66/0xb0

? unwind_get_return_address+0x5e/0xa0

? __pfx_stack_trace_consume_entry+0x10/0x10

? arch_stack_walk+0xa2/0xf0

? _raw_spin_lock_irqsave+0x8b/0xf0

? __pfx__raw_spin_lock_irqsave+0x10/0x10

? depot_alloc_stack+0x4c/0x1f0

? _raw_spin_unlock_irqrestore+0xe/0x30

? stack_depot_save_flags+0x35d/0x4f0

? kasan_save_stack+0x34/0x50

? kasan_save_stack+0x24/0x50

? mutex_lock+0x91/0xe0

? __pfx_mutex_lock+0x10/0x10

prepare_uprobe_buffer.part.0+0x2cd/0x500

uprobe_dispatcher+0x2c3/0x6a0

? __pfx_uprobe_dispatcher+0x10/0x10

? __kasan_slab_alloc+0x4d/0x90

handler_chain+0xdd/0x3e0

handle_swbp+0x26e/0x3d0

? __pfx_handle_swbp+0x10/0x10

? uprobe_pre_sstep_notifier+0x151/0x1b0

irqentry_exit_to_user_mode+0xe2/0x1b0

asm_exc_int3+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

store_trace_args() out-of-memory access.