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tracing/probes: Fix MAX_TRACE_ARGS limit handling
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When creating a trace_probe we would set nr_args prior to truncating the
arguments to MAX_TRACE_ARGS. However, we would only initialize arguments
up to the limit.

This caused invalid memory access when attempting to set up probes with
more than 128 fetchargs.

  BUG: kernel NULL pointer dereference, address: 0000000000000020
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 0 P4D 0
  Oops: Oops: 0000 [Rust-for-Linux#1] PREEMPT SMP PTI
  CPU: 0 UID: 0 PID: 1769 Comm: cat Not tainted 6.11.0-rc7+ Rust-for-Linux#8
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-1.fc39 04/01/2014
  RIP: 0010:__set_print_fmt+0x134/0x330

Resolve the issue by applying the MAX_TRACE_ARGS limit earlier. Return
an error when there are too many arguments instead of silently
truncating.

Link: https://lore.kernel.org/all/[email protected]/

Fixes: 035ba76 ("tracing/probes: cleanup: Set trace_probe::nr_args at trace_probe_init")
Signed-off-by: Mikel Rychliski <[email protected]>
Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
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mikelr authored and mhiramat committed Oct 23, 2024
1 parent aff1871 commit 73f3508
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Showing 4 changed files with 19 additions and 4 deletions.
7 changes: 6 additions & 1 deletion kernel/trace/trace_eprobe.c
Original file line number Diff line number Diff line change
Expand Up @@ -912,6 +912,11 @@ static int __trace_eprobe_create(int argc, const char *argv[])
}
}

if (argc - 2 > MAX_TRACE_ARGS) {
ret = -E2BIG;
goto error;
}

mutex_lock(&event_mutex);
event_call = find_and_get_event(sys_name, sys_event);
ep = alloc_event_probe(group, event, event_call, argc - 2);
Expand All @@ -937,7 +942,7 @@ static int __trace_eprobe_create(int argc, const char *argv[])

argc -= 2; argv += 2;
/* parse arguments */
for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
for (i = 0; i < argc; i++) {
trace_probe_log_set_index(i + 2);
ret = trace_eprobe_tp_update_arg(ep, argv, i);
if (ret)
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6 changes: 5 additions & 1 deletion kernel/trace/trace_fprobe.c
Original file line number Diff line number Diff line change
Expand Up @@ -1187,6 +1187,10 @@ static int __trace_fprobe_create(int argc, const char *argv[])
argc = new_argc;
argv = new_argv;
}
if (argc > MAX_TRACE_ARGS) {
ret = -E2BIG;
goto out;
}

ret = traceprobe_expand_dentry_args(argc, argv, &dbuf);
if (ret)
Expand All @@ -1203,7 +1207,7 @@ static int __trace_fprobe_create(int argc, const char *argv[])
}

/* parse arguments */
for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
for (i = 0; i < argc; i++) {
trace_probe_log_set_index(i + 2);
ctx.offset = 0;
ret = traceprobe_parse_probe_arg(&tf->tp, i, argv[i], &ctx);
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6 changes: 5 additions & 1 deletion kernel/trace/trace_kprobe.c
Original file line number Diff line number Diff line change
Expand Up @@ -1013,6 +1013,10 @@ static int __trace_kprobe_create(int argc, const char *argv[])
argc = new_argc;
argv = new_argv;
}
if (argc > MAX_TRACE_ARGS) {
ret = -E2BIG;
goto out;
}

ret = traceprobe_expand_dentry_args(argc, argv, &dbuf);
if (ret)
Expand All @@ -1029,7 +1033,7 @@ static int __trace_kprobe_create(int argc, const char *argv[])
}

/* parse arguments */
for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
for (i = 0; i < argc; i++) {
trace_probe_log_set_index(i + 2);
ctx.offset = 0;
ret = traceprobe_parse_probe_arg(&tk->tp, i, argv[i], &ctx);
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4 changes: 3 additions & 1 deletion kernel/trace/trace_uprobe.c
Original file line number Diff line number Diff line change
Expand Up @@ -565,6 +565,8 @@ static int __trace_uprobe_create(int argc, const char **argv)

if (argc < 2)
return -ECANCELED;
if (argc - 2 > MAX_TRACE_ARGS)
return -E2BIG;

if (argv[0][1] == ':')
event = &argv[0][2];
Expand Down Expand Up @@ -690,7 +692,7 @@ static int __trace_uprobe_create(int argc, const char **argv)
tu->filename = filename;

/* parse arguments */
for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
for (i = 0; i < argc; i++) {
struct traceprobe_parse_context ctx = {
.flags = (is_return ? TPARG_FL_RETURN : 0) | TPARG_FL_USER,
};
Expand Down

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