On Wed, Mar 10, 2021 at 04:30:21PM -0600, Tyrel Datwyler wrote: > Both add_slot_store() and remove_slot_store() try to fix up the drc_name > copied from the store buffer by placing a NULL terminator at nbyte + 1 > or in place of a '\n' if present. However, the static buffer that we > copy the drc_name data into is not zeored and can contain anything past > the n-th byte. This is problematic if a '\n' byte appears in that buffer > after nbytes and the string copied into the store buffer was not NULL > terminated to start with as the strchr() search for a '\n' byte will mark > this incorrectly as the end of the drc_name string resulting in a drc_name > string that contains garbage data after the n-th byte. The following > debugging shows an example of the drmgr utility writing "PHB 4543" to > the add_slot sysfs attribute, but add_slot_store logging a corrupted > string value. > > [135823.702864] drmgr: drmgr: -c phb -a -s PHB 4543 -d 1 > [135823.702879] add_slot_store: drc_name = PHB 4543°|<82>!, rc = -19 > > Fix this by NULL terminating the string when we copy it into our static > buffer by coping nbytes + 1 of data from the store buffer. The code has Why is it OK to copy nbytes + 1 and why is it expected that the buffer contains a nul after the content? Isn't it much saner to just nul terminate the string after copying? diff --git a/drivers/pci/hotplug/rpadlpar_sysfs.c b/drivers/pci/hotplug/rpadlpar_sysfs.c index cdbfa5df3a51..cfbad67447da 100644 --- a/drivers/pci/hotplug/rpadlpar_sysfs.c +++ b/drivers/pci/hotplug/rpadlpar_sysfs.c @@ -35,11 +35,11 @@ static ssize_t add_slot_store(struct kobject *kobj, struct kobj_attribute *attr, return 0; memcpy(drc_name, buf, nbytes); + &drc_name[nbytes] = '\0'; end = strchr(drc_name, '\n'); - if (!end) - end = &drc_name[nbytes]; - *end = '\0'; + if (end) + *end = '\0'; rc = dlpar_add_slot(drc_name); if (rc) @@ -66,11 +66,11 @@ static ssize_t remove_slot_store(struct kobject *kobj, return 0; memcpy(drc_name, buf, nbytes); + &drc_name[nbytes] = '\0'; end = strchr(drc_name, '\n'); - if (!end) - end = &drc_name[nbytes]; - *end = '\0'; + if (end) + *end = '\0'; rc = dlpar_remove_slot(drc_name); if (rc) Thanks Michal > already made sure that nbytes is not >= MAX_DRC_NAME_LEN and the store > buffer is guaranteed to be zeroed beyond the nth-byte of data copied > from the user. Further, since the string is now NULL terminated the code > only needs to change '\n' to '\0' when present. > > Signed-off-by: Tyrel Datwyler <tyreld@xxxxxxxxxxxxx> > --- > drivers/pci/hotplug/rpadlpar_sysfs.c | 14 ++++++-------- > 1 file changed, 6 insertions(+), 8 deletions(-) > > diff --git a/drivers/pci/hotplug/rpadlpar_sysfs.c b/drivers/pci/hotplug/rpadlpar_sysfs.c > index cdbfa5df3a51..375087921284 100644 > --- a/drivers/pci/hotplug/rpadlpar_sysfs.c > +++ b/drivers/pci/hotplug/rpadlpar_sysfs.c > @@ -34,12 +34,11 @@ static ssize_t add_slot_store(struct kobject *kobj, struct kobj_attribute *attr, > if (nbytes >= MAX_DRC_NAME_LEN) > return 0; > > - memcpy(drc_name, buf, nbytes); > + memcpy(drc_name, buf, nbytes + 1); > > end = strchr(drc_name, '\n'); > - if (!end) > - end = &drc_name[nbytes]; > - *end = '\0'; > + if (end) > + *end = '\0'; > > rc = dlpar_add_slot(drc_name); > if (rc) > @@ -65,12 +64,11 @@ static ssize_t remove_slot_store(struct kobject *kobj, > if (nbytes >= MAX_DRC_NAME_LEN) > return 0; > > - memcpy(drc_name, buf, nbytes); > + memcpy(drc_name, buf, nbytes + 1); > > end = strchr(drc_name, '\n'); > - if (!end) > - end = &drc_name[nbytes]; > - *end = '\0'; > + if (end) > + *end = '\0'; > > rc = dlpar_remove_slot(drc_name); > if (rc) > -- > 2.27.0 >
