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SUNRPC: Fix the svc_deferred_event trace class

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Fix a NULL deref crash that occurs when an svc_rqst is deferred
while the sunrpc tracing subsystem is enabled. svc_revisit() sets
dr->xprt to NULL, so it can't be relied upon in the tracepoint to
provide the remote's address.

Unfortunately we can't revert the "svc_deferred_class" hunk in
commit ece200ddd5 ("sunrpc: Save remote presentation address in
svc_xprt for trace events") because there is now a specific check
of event format specifiers for unsafe dereferences. The warning
that check emits is:

  event svc_defer_recv has unsafe dereference of argument 1

A "%pISpc" format specifier with a "struct sockaddr *" is indeed
flagged by this check.

Instead, take the brute-force approach used by the svcrdma_qp_error
tracepoint. Convert the dr::addr field into a presentation address
in the TP_fast_assign() arm of the trace event, and store that as
a string. This fix can be backported to -stable kernels.

In the meantime, commit c6ced22997 ("tracing: Update print fmt
check to handle new __get_sockaddr() macro") is now in v5.18, so
this wonky fix can be replaced with __sockaddr() and friends
properly during the v5.19 merge window.

Fixes: ece200ddd5 ("sunrpc: Save remote presentation address in svc_xprt for trace events")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
Chuck Lever 2022-04-06 13:51:32 -04:00
parent 773f91b2cf
commit 4d5004451a
1 changed files with 4 additions and 3 deletions
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7
include/trace/events/sunrpc.h
View File

@ -2017,17 +2017,18 @@ DECLARE_EVENT_CLASS(svc_deferred_event,
TP_STRUCT__entry(
__field(const void *, dr)
__field(u32, xid)
__string(addr, dr->xprt->xpt_remotebuf)
__array(__u8, addr, INET6_ADDRSTRLEN + 10)
),
TP_fast_assign(
__entry->dr = dr;
__entry->xid = be32_to_cpu(*(__be32 *)(dr->args +
(dr->xprt_hlen>>2)));
__assign_str(addr, dr->xprt->xpt_remotebuf);
snprintf(__entry->addr, sizeof(__entry->addr) - 1,
"%pISpc", (struct sockaddr *)&dr->addr);
),
TP_printk("addr=%s dr=%p xid=0x%08x", __get_str(addr), __entry->dr,
TP_printk("addr=%s dr=%p xid=0x%08x", __entry->addr, __entry->dr,
__entry->xid)
);