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linux/include/trace/events/9p.h
JP Kobryn a931c68160 9p: prevent read overrun in protocol dump tracepoint 
An out of bounds read can occur within the tracepoint 9p_protocol_dump. In
the fast assign, there is a memcpy that uses a constant size of 32 (macro
named P9_PROTO_DUMP_SZ). When the copy is invoked, the source buffer is not
guaranteed match this size.  It was found that in some cases the source
buffer size is less than 32, resulting in a read that overruns.

The size of the source buffer seems to be known at the time of the
tracepoint being invoked. The allocations happen within p9_fcall_init(),
where the capacity field is set to the allocated size of the payload
buffer. This patch tries to fix the overrun by changing the fixed array to
a dynamically sized array and using the minimum of the capacity value or
P9_PROTO_DUMP_SZ as its length. The trace log statement is adjusted to
account for this. Note that the trace log no longer splits the payload on
the first 16 bytes. The full payload is now logged to a single line.

To repro the orignal problem, operations to a plan 9 managed resource can
be used. The simplest approach might just be mounting a shared filesystem
(between host and guest vm) using the plan 9 protocol while the tracepoint
is enabled.

mount -t 9p -o trans=virtio <mount_tag> <mount_path>

The bpftrace program below can be used to show the out of bounds read.
Note that a recent version of bpftrace is needed for the raw tracepoint
support. The script was tested using v0.19.0.

/* from include/net/9p/9p.h */
struct p9_fcall {
    u32 size;
    u8 id;
    u16 tag;
    size_t offset;
    size_t capacity;
    struct kmem_cache *cache;
    u8 *sdata;
    bool zc;
};

tracepoint:9p:9p_protocol_dump
{
    /* out of bounds read can happen when this tracepoint is enabled */
}

rawtracepoint:9p_protocol_dump
{
    $pdu = (struct p9_fcall *)arg1;
    $dump_sz = (uint64)32;

    if ($dump_sz > $pdu->capacity) {
        printf("reading %zu bytes from src buffer of %zu bytes\n",
            $dump_sz, $pdu->capacity);
    }
}

Signed-off-by: JP Kobryn <inwardvessel@gmail.com>
Message-ID: <20231204202321.22730-1-inwardvessel@gmail.com>
Fixes: 60ece0833b ("net/9p: allocate appropriate reduced message buffers")
Cc: stable@vger.kernel.org
Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
2023-12-05 21:18:44 +09:00

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/* SPDX-License-Identifier: GPL-2.0 */
#undef TRACE_SYSTEM
#define TRACE_SYSTEM 9p
#if !defined(_TRACE_9P_H) || defined(TRACE_HEADER_MULTI_READ)
#define _TRACE_9P_H
#include <linux/tracepoint.h>
#define P9_MSG_T \
EM( P9_TLERROR, "P9_TLERROR" ) \
EM( P9_RLERROR, "P9_RLERROR" ) \
EM( P9_TSTATFS, "P9_TSTATFS" ) \
EM( P9_RSTATFS, "P9_RSTATFS" ) \
EM( P9_TLOPEN, "P9_TLOPEN" ) \
EM( P9_RLOPEN, "P9_RLOPEN" ) \
EM( P9_TLCREATE, "P9_TLCREATE" ) \
EM( P9_RLCREATE, "P9_RLCREATE" ) \
EM( P9_TSYMLINK, "P9_TSYMLINK" ) \
EM( P9_RSYMLINK, "P9_RSYMLINK" ) \
EM( P9_TMKNOD, "P9_TMKNOD" ) \
EM( P9_RMKNOD, "P9_RMKNOD" ) \
EM( P9_TRENAME, "P9_TRENAME" ) \
EM( P9_RRENAME, "P9_RRENAME" ) \
EM( P9_TREADLINK, "P9_TREADLINK" ) \
EM( P9_RREADLINK, "P9_RREADLINK" ) \
EM( P9_TGETATTR, "P9_TGETATTR" ) \
EM( P9_RGETATTR, "P9_RGETATTR" ) \
EM( P9_TSETATTR, "P9_TSETATTR" ) \
EM( P9_RSETATTR, "P9_RSETATTR" ) \
EM( P9_TXATTRWALK, "P9_TXATTRWALK" ) \
EM( P9_RXATTRWALK, "P9_RXATTRWALK" ) \
EM( P9_TXATTRCREATE, "P9_TXATTRCREATE" ) \
EM( P9_RXATTRCREATE, "P9_RXATTRCREATE" ) \
EM( P9_TREADDIR, "P9_TREADDIR" ) \
EM( P9_RREADDIR, "P9_RREADDIR" ) \
EM( P9_TFSYNC, "P9_TFSYNC" ) \
EM( P9_RFSYNC, "P9_RFSYNC" ) \
EM( P9_TLOCK, "P9_TLOCK" ) \
EM( P9_RLOCK, "P9_RLOCK" ) \
EM( P9_TGETLOCK, "P9_TGETLOCK" ) \
EM( P9_RGETLOCK, "P9_RGETLOCK" ) \
EM( P9_TLINK, "P9_TLINK" ) \
EM( P9_RLINK, "P9_RLINK" ) \
EM( P9_TMKDIR, "P9_TMKDIR" ) \
EM( P9_RMKDIR, "P9_RMKDIR" ) \
EM( P9_TRENAMEAT, "P9_TRENAMEAT" ) \
EM( P9_RRENAMEAT, "P9_RRENAMEAT" ) \
EM( P9_TUNLINKAT, "P9_TUNLINKAT" ) \
EM( P9_RUNLINKAT, "P9_RUNLINKAT" ) \
EM( P9_TVERSION, "P9_TVERSION" ) \
EM( P9_RVERSION, "P9_RVERSION" ) \
EM( P9_TAUTH, "P9_TAUTH" ) \
EM( P9_RAUTH, "P9_RAUTH" ) \
EM( P9_TATTACH, "P9_TATTACH" ) \
EM( P9_RATTACH, "P9_RATTACH" ) \
EM( P9_TERROR, "P9_TERROR" ) \
EM( P9_RERROR, "P9_RERROR" ) \
EM( P9_TFLUSH, "P9_TFLUSH" ) \
EM( P9_RFLUSH, "P9_RFLUSH" ) \
EM( P9_TWALK, "P9_TWALK" ) \
EM( P9_RWALK, "P9_RWALK" ) \
EM( P9_TOPEN, "P9_TOPEN" ) \
EM( P9_ROPEN, "P9_ROPEN" ) \
EM( P9_TCREATE, "P9_TCREATE" ) \
EM( P9_RCREATE, "P9_RCREATE" ) \
EM( P9_TREAD, "P9_TREAD" ) \
EM( P9_RREAD, "P9_RREAD" ) \
EM( P9_TWRITE, "P9_TWRITE" ) \
EM( P9_RWRITE, "P9_RWRITE" ) \
EM( P9_TCLUNK, "P9_TCLUNK" ) \
EM( P9_RCLUNK, "P9_RCLUNK" ) \
EM( P9_TREMOVE, "P9_TREMOVE" ) \
EM( P9_RREMOVE, "P9_RREMOVE" ) \
EM( P9_TSTAT, "P9_TSTAT" ) \
EM( P9_RSTAT, "P9_RSTAT" ) \
EM( P9_TWSTAT, "P9_TWSTAT" ) \
EMe(P9_RWSTAT, "P9_RWSTAT" )
#define P9_FID_REFTYPE \
EM( P9_FID_REF_CREATE, "create " ) \
EM( P9_FID_REF_GET, "get " ) \
EM( P9_FID_REF_PUT, "put " ) \
EMe(P9_FID_REF_DESTROY, "destroy" )
/* Define EM() to export the enums to userspace via TRACE_DEFINE_ENUM() */
#undef EM
#undef EMe
#define EM(a, b) TRACE_DEFINE_ENUM(a);
#define EMe(a, b) TRACE_DEFINE_ENUM(a);
P9_MSG_T
P9_FID_REFTYPE
/* And also use EM/EMe to define helper enums -- once */
#ifndef __9P_DECLARE_TRACE_ENUMS_ONLY_ONCE
#define __9P_DECLARE_TRACE_ENUMS_ONLY_ONCE
#undef EM
#undef EMe
#define EM(a, b) a,
#define EMe(a, b) a
enum p9_fid_reftype {
P9_FID_REFTYPE
} __mode(byte);
#endif
/*
* Now redefine the EM() and EMe() macros to map the enums to the strings
* that will be printed in the output.
*/
#undef EM
#undef EMe
#define EM(a, b) { a, b },
#define EMe(a, b) { a, b }
#define show_9p_op(type) \
__print_symbolic(type, P9_MSG_T)
#define show_9p_fid_reftype(type) \
__print_symbolic(type, P9_FID_REFTYPE)
TRACE_EVENT(9p_client_req,
TP_PROTO(struct p9_client *clnt, int8_t type, int tag),
TP_ARGS(clnt, type, tag),
TP_STRUCT__entry(
__field( void *, clnt )
__field( __u8, type )
__field( __u32, tag )
),
TP_fast_assign(
__entry->clnt = clnt;
__entry->type = type;
__entry->tag = tag;
),
TP_printk("client %lu request %s tag %d",
(long)__entry->clnt, show_9p_op(__entry->type),
__entry->tag)
);
TRACE_EVENT(9p_client_res,
TP_PROTO(struct p9_client *clnt, int8_t type, int tag, int err),
TP_ARGS(clnt, type, tag, err),
TP_STRUCT__entry(
__field( void *, clnt )
__field( __u8, type )
__field( __u32, tag )
__field( __u32, err )
),
TP_fast_assign(
__entry->clnt = clnt;
__entry->type = type;
__entry->tag = tag;
__entry->err = err;
),
TP_printk("client %lu response %s tag %d err %d",
(long)__entry->clnt, show_9p_op(__entry->type),
__entry->tag, __entry->err)
);
/* dump 32 bytes of protocol data */
#define P9_PROTO_DUMP_SZ 32
TRACE_EVENT(9p_protocol_dump,
TP_PROTO(struct p9_client *clnt, struct p9_fcall *pdu),
TP_ARGS(clnt, pdu),
TP_STRUCT__entry(
__field( void *, clnt )
__field( __u8, type )
__field( __u16, tag )
__dynamic_array(unsigned char, line,
min_t(size_t, pdu->capacity, P9_PROTO_DUMP_SZ))
),
TP_fast_assign(
__entry->clnt = clnt;
__entry->type = pdu->id;
__entry->tag = pdu->tag;
memcpy(__get_dynamic_array(line), pdu->sdata,
__get_dynamic_array_len(line));
),
TP_printk("clnt %lu %s(tag = %d)\n%*ph\n",
(unsigned long)__entry->clnt, show_9p_op(__entry->type),
__entry->tag, __get_dynamic_array_len(line),
__get_dynamic_array(line))
);
TRACE_EVENT(9p_fid_ref,
TP_PROTO(struct p9_fid *fid, __u8 type),
TP_ARGS(fid, type),
TP_STRUCT__entry(
__field( int, fid )
__field( int, refcount )
__field( __u8, type )
),
TP_fast_assign(
__entry->fid = fid->fid;
__entry->refcount = refcount_read(&fid->count);
__entry->type = type;
),
TP_printk("%s fid %d, refcount %d",
show_9p_fid_reftype(__entry->type),
__entry->fid, __entry->refcount)
);
#endif /* _TRACE_9P_H */
/* This part must be outside protection */
#include <trace/define_trace.h>
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