On 3/13/21 1:17 AM, Michal Suchánek wrote: > 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?
It is my understanding that the store function buffer is allocated as a zeroed-page which the kernel copies up to at most (PAGE_SIZE - 1) of user data into. Anything after nbytes would therefore be zeroed. > > Isn't it much saner to just nul terminate the string after copying? At the cost of an extra line of code, sure. -Tyrel > > 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 <tyr...@linux.ibm.com> >> --- >> 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 >>
