On 5/27/20 7:04 PM, Andrew Morton wrote:
On Thu, 21 May 2020 17:22:50 +0200 Christoph Hellwig <hch@xxxxxx> wrote:
User the proper helper for kernel or userspace addresses based on
TASK_SIZE instead of the dangerous strncpy_from_unsafe function.
...
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -331,8 +331,11 @@ static void bpf_trace_copy_string(char *buf, void *unsafe_ptr, char fmt_ptype,
switch (fmt_ptype) {
case 's':
#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
- strncpy_from_unsafe(buf, unsafe_ptr, bufsz);
- break;
+ if ((unsigned long)unsafe_ptr < TASK_SIZE) {
+ strncpy_from_user_nofault(buf, user_ptr, bufsz);
+ break;
+ }
+ fallthrough;
#endif
case 'k':
strncpy_from_kernel_nofault(buf, unsafe_ptr, bufsz);
Another user of strncpy_from_unsafe() has popped up in linux-next's
bpf. I did the below, but didn't try very hard - it's probably wrong
if CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE=n?
Anyway, please take a look at all the bpf_trace.c changes in
linux-next.
From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: bpf:bpf_seq_printf(): handle potentially unsafe format string better
User the proper helper for kernel or userspace addresses based on
TASK_SIZE instead of the dangerous strncpy_from_unsafe function.
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/trace/bpf_trace.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
--- a/kernel/trace/bpf_trace.c~xxx
+++ a/kernel/trace/bpf_trace.c
@@ -588,15 +588,22 @@ BPF_CALL_5(bpf_seq_printf, struct seq_fi
}
if (fmt[i] == 's') {
+ void *unsafe_ptr;
+
/* try our best to copy */
if (memcpy_cnt >= MAX_SEQ_PRINTF_MAX_MEMCPY) {
err = -E2BIG;
goto out;
}
- err = strncpy_from_unsafe(bufs->buf[memcpy_cnt],
- (void *) (long) args[fmt_cnt],
- MAX_SEQ_PRINTF_STR_LEN);
+ unsafe_ptr = (void *)(long)args[fmt_cnt];
+ if ((unsigned long)unsafe_ptr < TASK_SIZE) {
+ err = strncpy_from_user_nofault(
+ bufs->buf[memcpy_cnt], unsafe_ptr,
+ MAX_SEQ_PRINTF_STR_LEN);
+ } else {
+ err = -EFAULT;
+ }
This probably not right.
The pointer stored at args[fmt_cnt] is a kernel pointer,
but it could be an invalid address and we do not want to fault.
Not sure whether it exists or not, we should use
strncpy_from_kernel_nofault()?
if (err < 0)
bufs->buf[memcpy_cnt][0] = '\0';
params[fmt_cnt] = (u64)(long)bufs->buf[memcpy_cnt];
_
