Re: [PATCH v13 12/12] tracing/wprobe: Support BTF struct offset resolution in set_wprobe trigger

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] get_offset_of_field() incorrectly evaluates the BTF kflag of the parent struct instead of the nested anonymous struct containing the field, leading to massively inflated offset calculations and bypassing bitfield validation.
- [Low] wprobe_trigger_log_err receives a truncated `glob` string, causing syntax error logs to place the caret out-of-bounds and hide the user's input.
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--- Patch [12]: [PATCH v13 12/12] tracing/wprobe: Support BTF struct offset resolution in set_wprobe trigger ---

commit 1da976d66d95af47e154412d3c1b912f8a6b4018
Author: Masami Hiramatsu (Google) [off-list ref]

tracing/wprobe: Support BTF struct offset resolution in set_wprobe trigger
    
Allow set_wprobe trigger to use BTF struct offset resolution to specify
the target address field.

Link: https://lore.kernel.org/all/59637b96946653393a7ad3c7de094094796b39c2.1785067572.git.wangjinchao600@gmail.com/ (local)

[ ... ]

[Severity: High]
Does this code check the kflag of the original parent type instead of the
anonymous struct that actually contains the field?

btf_find_struct_member() can return a field from a nested anonymous struct,
but if the parent struct and the anonymous struct have mismatched BTF kflags
(for example, the parent has kflag=0 while the anonymous struct has kflag=1
because it contains bitfields), using the parent's kflag here will cause
the bitfield size encoded in the upper 8 bits of the offset to be
misinterpreted as part of the byte offset.

This can add a massively inflated value to bitoffs and result in a wild
pointer dereference when the wprobe triggers.

+			/* Reject bitfield member access */
+			if (BTF_MEMBER_BITFIELD_SIZE(field->offset))
+				return -EINVAL;
+			bitoffs += anon_offs + BTF_MEMBER_BIT_OFFSET(field->offset);
+		} else {
+			bitoffs += anon_offs + field->offset;
+		}
+
+		field_name = next;
+		if (next) {
+			type = btf_type_skip_modifiers(btf, field->type, NULL);
+			if (!type)
+				return -ENOENT;
+		}
+	} while (next);
+	return bitoffs / BITS_PER_BYTE;
+}

[ ... ]

+static int wprobe_trigger_typecast_parse(char **field_str_ptr,
+					 struct trace_event_file *file,
+					 struct wprobe_trigger_data *wprobe_data,
+					 const char *glob)
+{
+	struct btf *btf __free(btf_put) = NULL;
+	const struct btf_type *type;
+	char *assign_field;
+	char *event_field;
+	char *type_field;
+	char *type_name;
+	char *offs;
+	long val = 0;
+	int id;
+	int adjust;
+
+	type_name = *field_str_ptr + 1;
+	event_field = strchr(type_name, ')');
+	if (!event_field) {
+		wprobe_trigger_log_err(file, glob, type_name - glob, DEREF_OPEN_BRACE);

[Severity: Low]
Will this log message place the caret out of bounds and hide the user's
input?

The glob string passed into wprobe_trigger_log_err() seems to be truncated
by an earlier strsep() call replacing the delimiter with a null terminator:

kernel/trace/trace_events_trigger.c:trigger_process_regex() {
    ...
    command = strsep(&next, ": \t");
    ...
}

Since glob is truncated to just the command name, calculating the offset as
type_name - glob can point far past the end of the printed text, making the
syntax error logs illegible.

+		return -EINVAL;
+	}

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Sashiko AI review · https://sashiko.dev/#/patchset/178739053919.1520941.17662338993878200834.stgit@devnote2?part=12