| Message ID | 20231204202321.22730-1-inwardvessel@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] 9p: prevent read overrun in protocol dump tracepoint | expand |
JP Kobryn wrote on Mon, Dec 04, 2023 at 12:23:20PM -0800: > 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> Thanks, I've updated the patch locally; will push to -next after testing later tonight and to Linus next week.
On Monday, December 4, 2023 9:23:20 PM CET JP Kobryn wrote: > 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> > --- Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com> > include/trace/events/9p.h | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > > diff --git a/include/trace/events/9p.h b/include/trace/events/9p.h > index 4dfa6d7f83ba..cd104a1343e2 100644 > --- 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)) > ); > > >
diff --git a/include/trace/events/9p.h b/include/trace/events/9p.h index 4dfa6d7f83ba..cd104a1343e2 100644 --- 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)) );
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> --- include/trace/events/9p.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)