Re: [Qemu-devel] [PATCH 02/22] sheepdog: avoid a few buffer overruns

[MORITA Kazutaka]

At Wed, 09 May 2012 11:46:10 +0200,
Kevin Wolf wrote:
> 
> Am 09.05.2012 11:23, schrieb Jim Meyering:
> > From: Jim Meyering <address@hidden>
> > 
> > * parse_vdiname: Use pstrcpy, not strncpy, when the destination
> > buffer must be NUL-terminated.
> > * sd_open: Likewise, avoid buffer overrun.
> > * do_sd_create: Likewise.  Leave the preceding memset, since
> > pstrcpy does not NUL-fill, and filename needs that.
> > * sd_snapshot_create: Add a comment/question.
> > * find_vdi_name: Remove a useless memset.
> > * sd_snapshot_goto: Remove a useless memset.
> > Use pstrcpy to NUL-terminate, because find_vdi_name requires
> > that its vdi arg (filename parameter) be NUL-terminated.
> > It seems ok not to NUL-fill the buffer.
> > Do the same for snapid: remove useless memset-0 (instead,
> > zero tag[0]).  Use pstrcpy, not strncpy.
> > * sd_snapshot_list: Use pstrcpy, not strncpy to write
> > into the ->name member.  Each must be NUL-terminated.
> > 
> > Signed-off-by: Jim Meyering <address@hidden>
> 
> Acked-by: Kevin Wolf <address@hidden>
> 
> Kazutaka, can you have a look? I think you may want to send patches on
> top to improve the places where Jim just put a comment.

Acked-by: MORITA Kazutaka <address@hidden>

I'll send a patch on top of this to address Jim's comments.

Kazutaka

> 
> Kevin
> 
> > ---
> >  block/sheepdog.c | 34 ++++++++++++++++++++++------------
> >  1 file changed, 22 insertions(+), 12 deletions(-)
> > 
> > diff --git a/block/sheepdog.c b/block/sheepdog.c
> > index 0ed6b19..f2579da 100644
> > --- a/block/sheepdog.c
> > +++ b/block/sheepdog.c
> > @@ -852,14 +852,14 @@ static int parse_vdiname(BDRVSheepdogState *s, const 
> > char *filename,
> >          s->port = 0;
> >      }
> > 
> > -    strncpy(vdi, p, SD_MAX_VDI_LEN);
> > +    pstrcpy(vdi, SD_MAX_VDI_LEN, p);
> > 
> >      p = strchr(vdi, ':');
> >      if (p) {
> >          *p++ = '\0';
> >          *snapid = strtoul(p, NULL, 10);
> >          if (*snapid == 0) {
> > -            strncpy(tag, p, SD_MAX_VDI_TAG_LEN);
> > +            pstrcpy(tag, SD_MAX_VDI_TAG_LEN, p);
> >          }
> >      } else {
> >          *snapid = CURRENT_VDI_ID; /* search current vdi */
> > @@ -886,7 +886,10 @@ static int find_vdi_name(BDRVSheepdogState *s, char 
> > *filename, uint32_t snapid,
> >          return -1;
> >      }
> > 
> > -    memset(buf, 0, sizeof(buf));
> > +    /* This pair of strncpy calls ensures that the buffer is zero-filled,
> > +     * which is desirable since we'll soon be sending those bytes, and
> > +     * don't want the send_req to read uninitialized data.
> > +     */
> >      strncpy(buf, filename, SD_MAX_VDI_LEN);
> >      strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
> > 
> > @@ -1129,7 +1132,7 @@ static int sd_open(BlockDriverState *bs, const char 
> > *filename, int flags)
> >      s->max_dirty_data_idx = 0;
> > 
> >      bs->total_sectors = s->inode.vdi_size / SECTOR_SIZE;
> > -    strncpy(s->name, vdi, sizeof(s->name));
> > +    pstrcpy(s->name, sizeof(s->name), vdi);
> >      qemu_co_mutex_init(&s->lock);
> >      g_free(buf);
> >      return 0;
> > @@ -1157,8 +1160,11 @@ static int do_sd_create(char *filename, int64_t 
> > vdi_size,
> >          return -EIO;
> >      }
> > 
> > +    /* FIXME: would it be better to fail (e.g., return -EIO) when filename
> > +     * does not fit in buf?  For now, just truncate and avoid buffer 
> > overrun.
> > +     */
> >      memset(buf, 0, sizeof(buf));
> > -    strncpy(buf, filename, SD_MAX_VDI_LEN);
> > +    pstrcpy(buf, sizeof(buf), filename);
> > 
> >      memset(&hdr, 0, sizeof(hdr));
> >      hdr.opcode = SD_OP_NEW_VDI;
> > @@ -1709,6 +1715,9 @@ static int sd_snapshot_create(BlockDriverState *bs, 
> > QEMUSnapshotInfo *sn_info)
> > 
> >      s->inode.vm_state_size = sn_info->vm_state_size;
> >      s->inode.vm_clock_nsec = sn_info->vm_clock_nsec;
> > +    /* It appears that inode.tag does not require a NUL terminator,
> > +     * which means this use of strncpy is ok.
> > +     */
> >      strncpy(s->inode.tag, sn_info->name, sizeof(s->inode.tag));
> >      /* we don't need to update entire object */
> >      datalen = SD_INODE_SIZE - sizeof(s->inode.data_vdi_id);
> > @@ -1771,13 +1780,13 @@ static int sd_snapshot_goto(BlockDriverState *bs, 
> > const char *snapshot_id)
> > 
> >      memcpy(old_s, s, sizeof(BDRVSheepdogState));
> > 
> > -    memset(vdi, 0, sizeof(vdi));
> > -    strncpy(vdi, s->name, sizeof(vdi));
> > +    pstrcpy(vdi, sizeof(vdi), s->name);
> > 
> > -    memset(tag, 0, sizeof(tag));
> >      snapid = strtoul(snapshot_id, NULL, 10);
> > -    if (!snapid) {
> > -        strncpy(tag, s->name, sizeof(tag));
> > +    if (snapid) {
> > +        tag[0] = 0;
> > +    } else {
> > +        pstrcpy(tag, sizeof(tag), s->name);
> >      }
> > 
> >      ret = find_vdi_name(s, vdi, snapid, tag, &vid, 1);
> > @@ -1905,8 +1914,9 @@ static int sd_snapshot_list(BlockDriverState *bs, 
> > QEMUSnapshotInfo **psn_tab)
> > 
> >              snprintf(sn_tab[found].id_str, sizeof(sn_tab[found].id_str), 
> > "%u",
> >                       inode.snap_id);
> > -            strncpy(sn_tab[found].name, inode.tag,
> > -                    MIN(sizeof(sn_tab[found].name), sizeof(inode.tag)));
> > +            pstrcpy(sn_tab[found].name,
> > +                    MIN(sizeof(sn_tab[found].name), sizeof(inode.tag)),
> > +                    inode.tag);
> >              found++;
> >          }
> >      }
> 
>