[PATCH 5.19 152/717] tracing: Fix reading strings from synthetic events

Greg Kroah-Hartman
2022-10-22T08:10:57Z

From: Steven Rostedt (Google) <rostedt@goodmis.org>

commit 0934ae9977c27133449b6dd8c6213970e7eece38 upstream.

The follow commands caused a crash:

# cd /sys/kernel/tracing
# echo 's:open char file[]' > dynamic_events
# echo 'hist:keys=common_pid:file=filename:onchange($file).trace(open,$file)' > events/syscalls/sys_enter_openat/trigger'
# echo 1 > events/synthetic/open/enable

BOOM!

The problem is that the synthetic event field "char file[]" will read
the value given to it as a string without any memory checks to make sure
the address is valid. The above example will pass in the user space
address and the sythetic event code will happily call strlen() on it
and then strscpy() where either one will cause an oops when accessing
user space addresses.

Use the helper functions from trace_kprobe and trace_eprobe that can
read strings safely (and actually succeed when the address is from user
space and the memory is mapped in).

Now the above can show:

packagekitd-1721 [000] ...2. 104.597170: open: file=/usr/lib/rpm/fileattrs/cmake.attr
in:imjournal-978 [006] ...2. 104.599642: open: file=/var/lib/rsyslog/imjournal.state.tmp
packagekitd-1721 [000] ...2. 104.626308: open: file=/usr/lib/rpm/fileattrs/debuginfo.attr

Link: https://lkml.kernel.org/r/20221012104534.826549315@goodmis.org

Cc: stable@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tom Zanussi <zanussi@kernel.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
Fixes: bd82631d7ccdc ("tracing: Add support for dynamic strings to synthetic events")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/trace/trace_events_synth.c | 23 +++++++++++++++++------
1 file changed, 17 insertions(+), 6 deletions(-)

--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -17,6 +17,8 @@
/* for gfp flag names */
#include <linux/trace_events.h>
#include <trace/events/mmflags.h>
+#include "trace_probe.h"
+#include "trace_probe_kernel.h"

#include "trace_synth.h"

@@ -409,6 +411,7 @@ static unsigned int trace_string(struct
{
unsigned int len = 0;
char *str_field;
+ int ret;

if (is_dynamic) {
u32 data_offset;
@@ -417,19 +420,27 @@ static unsigned int trace_string(struct
data_offset += event->n_u64 * sizeof(u64);
data_offset += data_size;

- str_field = (char *)entry + data_offset;
-
- len = strlen(str_val) + 1;
- strscpy(str_field, str_val, len);
+ len = kern_fetch_store_strlen((unsigned long)str_val);

data_offset |= len << 16;
*(u32 *)&entry->fields[*n_u64] = data_offset;

+ ret = kern_fetch_store_string((unsigned long)str_val, &entry->fields[*n_u64], entry);
+
(*n_u64)++;
} else {
str_field = (char *)&entry->fields[*n_u64];

- strscpy(str_field, str_val, STR_VAR_LEN_MAX);
+#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
+ if ((unsigned long)str_val < TASK_SIZE)
+ ret = strncpy_from_user_nofault(str_field, str_val, STR_VAR_LEN_MAX);
+ else
+#endif
+ ret = strncpy_from_kernel_nofault(str_field, str_val, STR_VAR_LEN_MAX);
+
+ if (ret < 0)
+ strcpy(str_field, FAULT_STRING);
+
(*n_u64) += STR_VAR_LEN_MAX / sizeof(u64);
}

@@ -462,7 +473,7 @@ static notrace void trace_event_raw_even
val_idx = var_ref_idx[field_pos];
str_val = (char *)(long)var_ref_vals[val_idx];

- len = strlen(str_val) + 1;
+ len = kern_fetch_store_strlen((unsigned long)str_val);

fields_size += len;
}