fprobe_fgraph_entry() reserves shadow stack space for every fprobe with
an exit handler, but only fills it for those whose entry handler returns
0. fgraph_reserve_data() does not clear the area, so fprobe_return()
parses the unused tail as headers left over from an earlier call, and an
exit handler can run twice or despite its entry handler asking to skip
it.
Write a zero word after the last entry to terminate the walk. A zeroed
slot does not decode to a NULL fprobe on the arches that encode the
header into one unsigned long, since arch_decode_fprobe_header_fp() ORs
in FPROBE_HEADER_MSB_PATTERN, so make read_fprobe_header() return NULL
for a zeroed slot.
Fixes: e0a384434ae1 ("tracing: fprobe: do not zero out unused fgraph_data")
Cc: [email protected]
Suggested-by: Masami Hiramatsu (Google) <[email protected]>
Signed-off-by: David Carlier <[email protected]>
---
kernel/trace/fprobe.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index 1e9b00997ff2..9f2d98181779 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -171,6 +171,11 @@ static inline bool write_fprobe_header(unsigned long
*stack,
static inline void read_fprobe_header(unsigned long *stack,
struct fprobe **fp, unsigned int
*size_words)
{
+ if (!*stack) {
+ *fp = NULL;
+ *size_words = 0;
+ return;
+ }
*fp = arch_decode_fprobe_header_fp(*stack);
*size_words = arch_decode_fprobe_header_size(*stack);
}
@@ -203,6 +208,12 @@ static inline void read_fprobe_header(unsigned long *stack,
{
struct __fprobe_header *fph = (struct __fprobe_header *)stack;
+ if (!*stack) {
+ *fp = NULL;
+ *size_words = 0;
+ return;
+ }
+
*fp = fph->fp;
*size_words = fph->size_words;
}
@@ -635,6 +646,10 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent
*trace, struct fgraph_ops
}
}
+ /* Terminate the list, fgraph_reserve_data() does not clear it. */
+ if (used && used < reserved_words)
+ fgraph_data[used] = 0;
+
/* If any exit_handler is set, data must be used. */
return used != 0;
}
--
2.55.0
