From: Qiao Ma mqaio@linux.alibaba.com
[ Upstream commit 373b9338c9722a368925d83bc622c596896b328e ]
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.
Link: https://lore.kernel.org/all/20241015060148.1108331-1-mqaio@linux.alibaba.com...
Fixes: dcad1a204f72 ("tracing/uprobes: Fetch args before reserving a ring buffer") Signed-off-by: Qiao Ma mqaio@linux.alibaba.com Signed-off-by: Masami Hiramatsu (Google) mhiramat@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Vamsi Krishna Brahmajosyula vamsi-krishna.brahmajosyula@broadcom.com --- kernel/trace/trace_uprobe.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c index e09eef65d32f..a6a3ff2a441e 100644 --- a/kernel/trace/trace_uprobe.c +++ b/kernel/trace/trace_uprobe.c @@ -862,6 +862,7 @@ struct uprobe_cpu_buffer { }; static struct uprobe_cpu_buffer __percpu *uprobe_cpu_buffer; static int uprobe_buffer_refcnt; +#define MAX_UCB_BUFFER_SIZE PAGE_SIZE
static int uprobe_buffer_init(void) { @@ -960,6 +961,11 @@ static struct uprobe_cpu_buffer *prepare_uprobe_buffer(struct trace_uprobe *tu, ucb = uprobe_buffer_get(); ucb->dsize = tu->tp.size + dsize;
+ if (WARN_ON_ONCE(ucb->dsize > MAX_UCB_BUFFER_SIZE)) { + ucb->dsize = MAX_UCB_BUFFER_SIZE; + dsize = MAX_UCB_BUFFER_SIZE - tu->tp.size; + } + store_trace_args(ucb->buf, &tu->tp, regs, esize, dsize);
return ucb; @@ -978,9 +984,6 @@ static void __uprobe_trace_func(struct trace_uprobe *tu,
WARN_ON(call != trace_file->event_call);
- if (WARN_ON_ONCE(ucb->dsize > PAGE_SIZE)) - return; - if (trace_trigger_soft_disabled(trace_file)) return;