migration: Use strnlen() for fixed-size string
GCC 8 introduced the -Wstringop-overflow, which detect buffer overflow
by string-modifying functions declared in <string.h>, such strncpy(),
used in global_state_store_running().
GCC indeed found an incorrect use of strlen(), because this array
is loaded by VMSTATE_BUFFER(runstate, GlobalState) then parsed
using qapi_enum_parse which does not get the buffer length.
Use strnlen() which returns sizeof(s->runstate) if the array is not
NUL-terminated, assert the size is within range, and enforce the array
to be NUL-terminated to avoid an overflow in qapi_enum_parse().
This fixes:
CC migration/global_state.o
qemu/migration/global_state.c: In function 'global_state_pre_save':
qemu/migration/global_state.c:109:15: error: 'strlen' argument 1 declared attribute 'nonstring' [-Werror=stringop-overflow=]
s->size = strlen((char *)s->runstate) + 1;
^~~~~~~~~~~~~~~~~~~~~~~~~~~
qemu/migration/global_state.c:24:13: note: argument 'runstate' declared here
uint8_t runstate[100] QEMU_NONSTRING;
^~~~~~~~
cc1: all warnings being treated as errors
make: *** [qemu/rules.mak:69: migration/global_state.o] Error 1
Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/migration/global_state.c b/migration/global_state.c
index 01805c5..2c8c447 100644
--- a/migration/global_state.c
+++ b/migration/global_state.c
@@ -89,6 +89,17 @@
s->received = true;
trace_migrate_global_state_post_load(runstate);
+ if (strnlen((char *)s->runstate,
+ sizeof(s->runstate)) == sizeof(s->runstate)) {
+ /*
+ * This condition should never happen during migration, because
+ * all runstate names are shorter than 100 bytes (the size of
+ * s->runstate). However, a malicious stream could overflow
+ * the qapi_enum_parse() call, so we force the last character
+ * to a NUL byte.
+ */
+ s->runstate[sizeof(s->runstate) - 1] = '\0';
+ }
r = qapi_enum_parse(&RunState_lookup, runstate, -1, &local_err);
if (r == -1) {
@@ -107,7 +118,8 @@
GlobalState *s = opaque;
trace_migrate_global_state_pre_save((char *)s->runstate);
- s->size = strlen((char *)s->runstate) + 1;
+ s->size = strnlen((char *)s->runstate, sizeof(s->runstate)) + 1;
+ assert(s->size <= sizeof(s->runstate));
return 0;
}
