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Subject[PATCH 3/4] fprobe: add recursion detection in fprobe_exit_handler
Date
fprobe_hander and fprobe_kprobe_handler has guarded ftrace recusion
detection but fprobe_exit_handler has not, which possibly introduce
recurive calls if the fprobe exit callback calls any traceable
functions. Checking in fprobe_hander or fprobe_kprobe_handler
is not enough and misses this case.

So add recusion free guard the same way as fprobe_hander and also
mark fprobe_exit_handler notrace. Since ftrace recursion check does
not employ ips, so here use entry_ip and entry_parent_ip the same as
fprobe_handler.

Signed-off-by: Ze Gao <zegao@tencent.com>
---
kernel/trace/fprobe.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index ad9a36c87ad9..cf982d4ab142 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -17,6 +17,7 @@
struct fprobe_rethook_node {
struct rethook_node node;
unsigned long entry_ip;
+ unsigned long entry_parent_ip;
char data[];
};

@@ -39,6 +40,7 @@ static inline notrace void __fprobe_handler(unsigned long ip, unsigned long
}
fpr = container_of(rh, struct fprobe_rethook_node, node);
fpr->entry_ip = ip;
+ fpr->entry_parent_ip = parent_ip;
if (fp->entry_data_size)
entry_data = fpr->data;
}
@@ -109,19 +111,30 @@ static void notrace fprobe_kprobe_handler(unsigned long ip, unsigned long parent
ftrace_test_recursion_unlock(bit);
}

-static void fprobe_exit_handler(struct rethook_node *rh, void *data,
+static void notrace fprobe_exit_handler(struct rethook_node *rh, void *data,
struct pt_regs *regs)
{
struct fprobe *fp = (struct fprobe *)data;
struct fprobe_rethook_node *fpr;
+ int bit;

if (!fp || fprobe_disabled(fp))
return;

fpr = container_of(rh, struct fprobe_rethook_node, node);

+ /* we need to assure no calls to traceable functions in-between the
+ * end of fprobe_handler and the beginning of fprobe_exit_handler.
+ */
+ bit = ftrace_test_recursion_trylock(fpr->entry_ip, fpr->entry_parent_ip);
+ if (bit < 0) {
+ fp->nmissed++;
+ return;
+ }
+
fp->exit_handler(fp, fpr->entry_ip, regs,
fp->entry_data_size ? (void *)fpr->data : NULL);
+ ftrace_test_recursion_unlock(bit);
}
NOKPROBE_SYMBOL(fprobe_exit_handler);

--
2.40.1
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