[PATCH v1 2/4] perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader

[Ian Rogers <irogers@google.com>]

Fix critical logic and boundary bugs in read_proc_maps_line() and caller.
Ensure any mid-line hex/dec/char parsing failure invokes io__drain_line()
to preserve line synchronization for subsequent map entries. Replace the
truncation bug (which improperly cleared over-length pathnames to an empty
string) with the kernel's standard '//toolong' fallback literal, and clamp
and pad structure size boundaries safely.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/synthetic-events.c | 183 ++++++++++++++++++++---------
 1 file changed, 127 insertions(+), 56 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index b75f9dcf4dbf..9161dc728e6e 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -291,6 +291,15 @@ static int perf_event__synthesize_fork(const struct perf_tool *tool,
 	return 0;
 }
 
+static void io__drain_line(struct io *io)
+{
+	int ch;
+
+	do {
+		ch = io__get_char(io);
+	} while (ch >= 0 && ch != '\n');
+}
+
 static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
 				u32 *prot, u32 *flags, __u64 *offset,
 				u32 *maj, u32 *min,
@@ -299,69 +308,121 @@ static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
 {
 	__u64 temp;
 	int ch;
-	char *start_pathname = pathname;
+	size_t written = 0;
+	bool overflowed = false;
 
-	if (io__get_hex(io, start) != '-')
+	if (io__get_hex(io, start) != '-') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
-	if (io__get_hex(io, end) != ' ')
+	}
+	if (io__get_hex(io, end) != ' ') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 
 	/* map protection and flags bits */
 	*prot = 0;
 	ch = io__get_char(io);
 	if (ch == 'r')
 		*prot |= PROT_READ;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 'w')
 		*prot |= PROT_WRITE;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 'x')
 		*prot |= PROT_EXEC;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 's')
 		*flags = MAP_SHARED;
 	else if (ch == 'p')
 		*flags = MAP_PRIVATE;
-	else
+	else {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
-	if (io__get_char(io) != ' ')
+	}
+	if (io__get_char(io) != ' ') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 
-	if (io__get_hex(io, offset) != ' ')
+	if (io__get_hex(io, offset) != ' ') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 
-	if (io__get_hex(io, &temp) != ':')
+	if (io__get_hex(io, &temp) != ':') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 	*maj = temp;
-	if (io__get_hex(io, &temp) != ' ')
+	if (io__get_hex(io, &temp) != ' ') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 	*min = temp;
 
 	ch = io__get_dec(io, inode);
 	if (ch != ' ') {
-		*pathname = '\0';
-		return ch == '\n';
+		if (ch == '\n') {
+			pathname[0] = '\0';
+			return true;
+		}
+		if (!io->eof)
+			io__drain_line(io);
+		return false;
 	}
+
 	do {
 		ch = io__get_char(io);
 	} while (ch == ' ');
+
 	while (true) {
-		if (ch < 0)
-			return false;
-		if (ch == '\0' || ch == '\n' ||
-		    (pathname + 1 - start_pathname) >= pathname_size) {
-			*pathname = '\0';
-			return true;
+		if (ch < 0) {
+			if (overflowed) {
+				strlcpy(pathname, "//toolong", pathname_size);
+				return true;
+			}
+			pathname[written] = '\0';
+			return written > 0;
 		}
-		*pathname++ = ch;
+		if (ch == '\0' || ch == '\n')
+			break;
+
+		if (written < (size_t)pathname_size - 1)
+			pathname[written++] = (char)ch;
+		else
+			overflowed = true;
 		ch = io__get_char(io);
 	}
+
+	if (overflowed)
+		strlcpy(pathname, "//toolong", pathname_size);
+	else
+		pathname[written] = '\0';
+
+	return true;
 }
 
 static void perf_record_mmap2__read_build_id(struct perf_record_mmap2 *event,
@@ -457,29 +518,25 @@ int perf_event__synthesize_mmap_events(const struct perf_tool *tool,
 	}
 	io__init(&io, io.fd, bf, sizeof(bf));
 
-	event->header.type = PERF_RECORD_MMAP2;
 	t = rdclock();
 
 	while (!io.eof) {
 		static const char anonstr[] = "//anon";
 		size_t size, aligned_size;
-
-		/* ensure null termination since stack will be reused. */
-		event->mmap2.filename[0] = '\0';
+		__u64 start, end, pgoff, ino;
+		u32 prot, flags, maj, min;
 
 		/* 00400000-0040c000 r-xp 00000000 fd:01 41038  /bin/cat */
-		if (!read_proc_maps_line(&io,
-					&event->mmap2.start,
-					&event->mmap2.len,
-					&event->mmap2.prot,
-					&event->mmap2.flags,
-					&event->mmap2.pgoff,
-					&event->mmap2.maj,
-					&event->mmap2.min,
-					&event->mmap2.ino,
-					sizeof(event->mmap2.filename),
-					event->mmap2.filename))
+		/* Read directly into event->mmap2.filename! */
+		if (!read_proc_maps_line(&io, &start, &end,
+					 &prot, &flags, &pgoff,
+					 &maj, &min, &ino,
+					 sizeof(event->mmap2.filename),
+					 event->mmap2.filename)) {
+			if (io.eof)
+				break;
 			continue;
+		}
 
 		if ((rdclock() - t) > timeout) {
 			pr_warning("Reading %s/proc/%d/task/%d/maps time out. "
@@ -487,50 +544,64 @@ int perf_event__synthesize_mmap_events(const struct perf_tool *tool,
 				   "the time limit by --proc-map-timeout\n",
 				   machine->root_dir, pid, pid);
 			truncation = true;
-			goto out;
 		}
 
-		event->mmap2.ino_generation = 0;
+		if (!strcmp(event->mmap2.filename, ""))
+			strcpy(event->mmap2.filename, anonstr);
+
+		if (hugetlbfs_mnt_len &&
+		    !strncmp(event->mmap2.filename, hugetlbfs_mnt, hugetlbfs_mnt_len)) {
+			strcpy(event->mmap2.filename, anonstr);
+			flags |= MAP_HUGETLB;
+		}
+
+		size = strlen(event->mmap2.filename) + 1;
+		aligned_size = PERF_ALIGN(size, sizeof(u64));
+
+		event->mmap2.header.type = PERF_RECORD_MMAP2;
 
 		/*
-		 * Just like the kernel, see __perf_event_mmap in kernel/perf_event.c
+		 * Just like the kernel, see perf_misc_flags() in
+		 * kernel/events/core.c
 		 */
 		if (machine__is_host(machine))
 			event->header.misc = PERF_RECORD_MISC_USER;
 		else
 			event->header.misc = PERF_RECORD_MISC_GUEST_USER;
 
-		if ((event->mmap2.prot & PROT_EXEC) == 0) {
-			if (!mmap_data || (event->mmap2.prot & PROT_READ) == 0)
+		if ((prot & PROT_EXEC) == 0) {
+			if (!mmap_data || (prot & PROT_READ) == 0) {
+				if (truncation)
+					break;
 				continue;
+			}
 
 			event->header.misc |= PERF_RECORD_MISC_MMAP_DATA;
 		}
 
-out:
 		if (truncation)
 			event->header.misc |= PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT;
 
-		if (!strcmp(event->mmap2.filename, ""))
-			strcpy(event->mmap2.filename, anonstr);
+		event->mmap2.header.size =
+			offsetof(struct perf_record_mmap2, filename) +
+			aligned_size;
 
-		if (hugetlbfs_mnt_len &&
-		    !strncmp(event->mmap2.filename, hugetlbfs_mnt,
-			     hugetlbfs_mnt_len)) {
-			strcpy(event->mmap2.filename, anonstr);
-			event->mmap2.flags |= MAP_HUGETLB;
-		}
+		/* Zero the padding and ID header trailer safely! */
+		memset(event->mmap2.filename + size, 0,
+		       (aligned_size - size) + machine->id_hdr_size);
 
-		size = strlen(event->mmap2.filename) + 1;
-		aligned_size = PERF_ALIGN(size, sizeof(u64));
-		event->mmap2.len -= event->mmap.start;
-		event->mmap2.header.size = (sizeof(event->mmap2) -
-					(sizeof(event->mmap2.filename) - aligned_size));
-		memset(event->mmap2.filename + size, 0, machine->id_hdr_size +
-			(aligned_size - size));
 		event->mmap2.header.size += machine->id_hdr_size;
+		event->mmap2.start = start;
+		event->mmap2.len = end - start;
+		event->mmap2.pgoff = pgoff;
+		event->mmap2.maj = maj;
+		event->mmap2.min = min;
+		event->mmap2.ino = ino;
+		event->mmap2.ino_generation = 0;
 		event->mmap2.pid = tgid;
 		event->mmap2.tid = pid;
+		event->mmap2.prot = prot;
+		event->mmap2.flags = flags;
 
 		if (!symbol_conf.no_buildid_mmap2)
 			perf_record_mmap2__read_build_id(&event->mmap2, machine, false);
-- 
2.55.0.229.g6434b31f56-goog