6.6-stable review patch. If anyone has any objections, please let me know.
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From: JP Kobryn inwardvessel@gmail.com
commit a931c6816078af3e306e0f444f492396ce40de31 upstream.
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: 60ece0833b6c ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/trace/events/9p.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
--- a/include/trace/events/9p.h +++ b/include/trace/events/9p.h @@ -178,18 +178,21 @@ TRACE_EVENT(9p_protocol_dump, __field( void *, clnt ) __field( __u8, type ) __field( __u16, tag ) - __array( unsigned char, line, P9_PROTO_DUMP_SZ ) + __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(__entry->line, pdu->sdata, P9_PROTO_DUMP_SZ); + memcpy(__get_dynamic_array(line), pdu->sdata, + __get_dynamic_array_len(line)); ), - TP_printk("clnt %lu %s(tag = %d)\n%.3x: %16ph\n%.3x: %16ph\n", + TP_printk("clnt %lu %s(tag = %d)\n%*ph\n", (unsigned long)__entry->clnt, show_9p_op(__entry->type), - __entry->tag, 0, __entry->line, 16, __entry->line + 16) + __entry->tag, __get_dynamic_array_len(line), + __get_dynamic_array(line)) );