On Tue, 2019-04-30 at 15:07 +0200, Oliver Neukum wrote: > dvb_usb_device_exit() frees and uses the device name in that order > Fix by storing the name in a buffer before freeing it > > v2: fixed style issues > v3: strscpy used and variable names changed > v4: really use strscpy everywhere > > Signed-off-by: Oliver Neukum <oneukum@xxxxxxxx> > Reported-by: syzbot+26ec41e9f788b3eba396@xxxxxxxxxxxxxxxxxxxxxxxxx This doesn't fix that bug (and I don't think it fixes a bug at all). The name string is static and doesn't get freed until the module it's in is freed. Look again at the stack traces in <https://syzkaller.appspot.com/bug?extid=26ec41e9f788b3eba396>: > Allocated by task 21: [...] > kmemdup+0x23/0x50 mm/util.c:118 > kmemdup include/linux/string.h:428 [inline] > dw2102_probe+0x62c/0xc50 drivers/media/usb/dvb-usb/dw2102.c:2375 [...] > Freed by task 21: [...] > kfree+0xce/0x290 mm/slub.c:3958 > dw2102_probe+0x876/0xc50 drivers/media/usb/dvb-usb/dw2102.c:2409 So, d->desc was freed during probe, and is a dangling pointer before dvb_usb_device_exit() runs at all. The bug seems to have been introduced by: commit 299c7007e93645067e1d2743f4e50156de78c4ff Author: Anton Vasilyev <vasilyev@xxxxxxxxx> Date: Mon Jul 23 13:04:54 2018 -0400 media: dw2102: Fix memleak on sequence of probes Ben. > --- > drivers/media/usb/dvb-usb/dvb-usb-init.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/drivers/media/usb/dvb-usb/dvb-usb-init.c b/drivers/media/usb/dvb-usb/dvb-usb-init.c > index 99951e02a880..dd063a736df5 100644 > --- a/drivers/media/usb/dvb-usb/dvb-usb-init.c > +++ b/drivers/media/usb/dvb-usb/dvb-usb-init.c > @@ -287,12 +287,15 @@ EXPORT_SYMBOL(dvb_usb_device_init); > void dvb_usb_device_exit(struct usb_interface *intf) > { > struct dvb_usb_device *d = usb_get_intfdata(intf); > - const char *name = "generic DVB-USB module"; > + const char *default_name = "generic DVB-USB module"; > + char name[40]; > > usb_set_intfdata(intf, NULL); > if (d != NULL && d->desc != NULL) { > - name = d->desc->name; > + strscpy(name, d->desc->name, sizeof(name)); > dvb_usb_exit(d); > + } else { > + strscpy(name, default_name, sizeof(name)); > } > info("%s successfully deinitialized and disconnected.", name); > -- Ben Hutchings Experience is what causes a person to make new mistakes instead of old ones.
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