From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:38366) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h2LSC-0007RI-BR for qemu-devel@nongnu.org; Fri, 08 Mar 2019 14:46:49 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1h2LSB-0004Uv-ET for qemu-devel@nongnu.org; Fri, 08 Mar 2019 14:46:48 -0500 Received: from mx1.redhat.com ([209.132.183.28]:50766) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1h2LSB-0004Su-4m for qemu-devel@nongnu.org; Fri, 08 Mar 2019 14:46:47 -0500 From: Bandan Das References: <20190307095441.31921-1-kraxel@redhat.com> <20190307095441.31921-4-kraxel@redhat.com> Date: Fri, 08 Mar 2019 14:46:41 -0500 In-Reply-To: (Peter Maydell's message of "Fri, 8 Mar 2019 17:06:08 +0000") Message-ID: MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PULL 3/4] usb-mtp: prevent null dereference while deleting objects List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: Gerd Hoffmann , QEMU Developers Peter Maydell writes: > On Thu, 7 Mar 2019 at 09:56, Gerd Hoffmann wrote: >> >> From: Bandan Das >> >> Spotted by Coverity: CID 1399144 >> >> Signed-off-by: Bandan Das >> Message-id: 20190306210409.14842-4-bsd@redhat.com >> Signed-off-by: Gerd Hoffmann >> --- >> hw/usb/dev-mtp.c | 4 +--- >> 1 file changed, 1 insertion(+), 3 deletions(-) >> >> diff --git a/hw/usb/dev-mtp.c b/hw/usb/dev-mtp.c >> index 1f22284949df..06e376bcd211 100644 >> --- a/hw/usb/dev-mtp.c >> +++ b/hw/usb/dev-mtp.c >> @@ -1177,9 +1177,7 @@ static int usb_mtp_deletefn(MTPState *s, MTPObject *o, uint32_t trans) >> usb_mtp_object_free_one(s, o); >> success = true; >> } >> - } >> - >> - if (o->format == FMT_ASSOCIATION) { >> + } else if (o->format == FMT_ASSOCIATION) { >> if (rmdir(o->path)) { >> partial_delete = true; >> } else { >> -- > > Hi; following this change Coverity now complains (CID 1399414) > about dead code later in the file: > > In this set of if/else clauses, either we > set partial_delete to true, or we set success to > true, but never both: > > if (o->format == FMT_UNDEFINED_OBJECT) { > if (remove(o->path)) { > partial_delete = true; > } else { > usb_mtp_object_free_one(s, o); > success = true; > } > } else if (o->format == FMT_ASSOCIATION) { > if (rmdir(o->path)) { > partial_delete = true; > } else { > usb_mtp_object_free_one(s, o); > success = true; > } > } > > and so here: > > if (success && partial_delete) { > return PARTIAL_DELETE; > } > > the condition can never be true and the code inside > the if () {} is dead. > > When is the routine intended to return the PARTIAL_DELETE > return value ? > This is very broken! I think something like this should work: diff --git a/hw/usb/dev-mtp.c b/hw/usb/dev-mtp.c index 06e376bcd2..87a4bfb415 100644 --- a/hw/usb/dev-mtp.c +++ b/hw/usb/dev-mtp.c @@ -1138,8 +1138,8 @@ static MTPData *usb_mtp_get_object_prop_value(MTPState *s, MTPControl *c, /* Return correct return code for a delete event */ enum { ALL_DELETE, - PARTIAL_DELETE, READ_ONLY, + PARTIAL_DELETE, }; /* Assumes that children, if any, have been already freed */ @@ -1155,8 +1155,7 @@ static void usb_mtp_object_free_one(MTPState *s, MTPObject *o) static int usb_mtp_deletefn(MTPState *s, MTPObject *o, uint32_t trans) { MTPObject *iter, *iter2; - bool partial_delete = false; - bool success = false; + int ret = 0; /* * TODO: Add support for Protection Status @@ -1165,34 +1164,28 @@ static int usb_mtp_deletefn(MTPState *s, MTPObject *o, uint32_t trans) QLIST_FOREACH(iter, &o->children, list) { if (iter->format == FMT_ASSOCIATION) { QLIST_FOREACH(iter2, &iter->children, list) { - usb_mtp_deletefn(s, iter2, trans); + ret |= usb_mtp_deletefn(s, iter2, trans); } } } if (o->format == FMT_UNDEFINED_OBJECT) { if (remove(o->path)) { - partial_delete = true; + ret |= READ_ONLY; } else { usb_mtp_object_free_one(s, o); - success = true; + ret |= ALL_DELETE; } } else if (o->format == FMT_ASSOCIATION) { if (rmdir(o->path)) { - partial_delete = true; + ret |= READ_ONLY; } else { usb_mtp_object_free_one(s, o); - success = true; + ret |= ALL_DELETE; } } - if (success && partial_delete) { - return PARTIAL_DELETE; - } - if (!success && partial_delete) { - return READ_ONLY; - } - return ALL_DELETE; + return ret; } static void usb_mtp_object_delete(MTPState *s, uint32_t handle, I will test this and send a patch... Bandan > thanks > -- PMM