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Subject[for-next][PATCH 4/8] ftrace: Reset fgd->hash in ftrace_graph_write()
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

fgd->hash is saved and then freed, but is never reset to either
ftrace_graph_hash nor ftrace_graph_notrace_hash. But if multiple reads are
performed, then the freed hash could be accessed again.

# cd /sys/kernel/debug/tracing
# head -1000 available_filter_functions > /tmp/funcs
# cat /tmp/funcs > set_graph_function

Causes:

general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC
Modules linked in: [...]
CPU: 2 PID: 1337 Comm: cat Not tainted 4.10.0-rc2-test-00010-g6b052e9 #32
Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01 v02.05 05/07/2012
task: ffff880113a12200 task.stack: ffffc90001940000
RIP: 0010:free_ftrace_hash+0x7c/0x160
RSP: 0018:ffffc90001943db0 EFLAGS: 00010246
RAX: 6b6b6b6b6b6b6b6b RBX: 6b6b6b6b6b6b6b6b RCX: 6b6b6b6b6b6b6b6b
RDX: 0000000000000002 RSI: 0000000000000001 RDI: ffff8800ce1e1d40
RBP: ffff8800ce1e1d50 R08: 0000000000000000 R09: 0000000000006400
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff8800ce1e1d40 R14: 0000000000004000 R15: 0000000000000001
FS: 00007f9408a07740(0000) GS:ffff88011e500000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000aee1f0 CR3: 0000000116bb4000 CR4: 00000000001406e0
Call Trace:
? ftrace_graph_write+0x150/0x190
? __vfs_write+0x1f6/0x210
? __audit_syscall_entry+0x17f/0x200
? rw_verify_area+0xdb/0x210
? _cond_resched+0x2b/0x50
? __sb_start_write+0xb4/0x130
? vfs_write+0x1c8/0x330
? SyS_write+0x62/0xf0
? do_syscall_64+0xa3/0x1b0
? entry_SYSCALL64_slow_path+0x25/0x25
Code: 01 48 85 db 0f 84 92 00 00 00 b8 01 00 00 00 d3 e0 85 c0 7e 3f 83 e8 01 48 8d 6f 10 45 31 e4 4c 8d 34 c5 08 00 00 00 49 8b 45 08 <4a> 8b 34 20 48 85 f6 74 13 48 8b 1e 48 89 ef e8 20 fa ff ff 48
RIP: free_ftrace_hash+0x7c/0x160 RSP: ffffc90001943db0
---[ end trace 999b48216bf4b393 ]---

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/ftrace.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index a9cfc8713198..b7df0dcf8652 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -4858,10 +4858,13 @@ ftrace_graph_write(struct file *file, const char __user *ubuf,
if (!new_hash)
ret = -ENOMEM;

- if (fgd->type == GRAPH_FILTER_FUNCTION)
+ if (fgd->type == GRAPH_FILTER_FUNCTION) {
rcu_assign_pointer(ftrace_graph_hash, new_hash);
- else
+ fgd->hash = ftrace_graph_hash;
+ } else {
rcu_assign_pointer(ftrace_graph_notrace_hash, new_hash);
+ fgd->hash = ftrace_graph_notrace_hash;
+ }

mutex_unlock(&graph_lock);

--
2.10.2

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