GRUB coverity fixes for CIDs 314020 and 314023

GRUB coverity fixes for CIDs 314020 and 314023

[Jagannathan Raman]

Hi,

This series addresses a couple of untrusted loop bounds flagged by
Coverity in "grub-core/fs/zfs". Both the bugs addressed in this series
are of the same type - caused by downcast of pointer from a strict type
to a less strict type.

Please share your thoughts on this.

Thank you!
--
Jag

Jagannathan Raman (2):
  fs/zfs/zfs.c: make_mdn() - avoid pointer downcasting
  fs/zfs/zfs.c: zfs_mount() - avoid pointer downcasting

 grub-core/fs/zfs/zfs.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

-- 
2.31.1

[PATCH 1/2] fs/zfs/zfs.c: make_mdn() - avoid pointer downcasting

[Jagannathan Raman]

Coverity reports that the while loop in the following function uses
tainted data as boundary:
  fill_fs_info() -> dnode_get() -> zfs_log2()

The tainted originated from:
  fill_fs_info() -> make_mdn()

The defect type is "Untrusted loop bound" caused as a result of
"tainted_data_downcast". Coverity does not like the pointer downcast
here and we need to address it.

We believe Coverity flags pointer downcast for the following two
reasons:
1. External data: The pointer downcast could indicate that the source is
  external data, which we need to further sanitize - such as verifying its
  limits. In this case, the data is read from an external source, which is
  a disk. But, zio_read(), which reads the data from the disk, sanitizes it
  using a checksum. checksum is the best facility that ZFS offers to verify
  external data, and we don't believe a better way exists. Therefore, no
  further action is possible for this.

2. Corruption due to alignment: downcasting a pointer from a strict type
  to less strict type could result in data corruption. For example, the
  following cast would corrupt because uint32_t is 4-byte aligned, and
  won't be able to point to 0x1003 which is not 4-byte aligned.
    uint8_t *ptr = 0x1003;
    uint32_t *word = ptr; (incorrect, alignment issues)

  This patch converts the "osp" pointer in make_mdn() from a "void" type
  to "objset_phys_t" type to address this issue.

We are not sure if there are any other reasons why Coverity flags the
downcast. However, the fix for alignment issue masks/suppresses any
other issues from showing up.

Fixes: CID 314020

Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
---
 grub-core/fs/zfs/zfs.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/grub-core/fs/zfs/zfs.c b/grub-core/fs/zfs/zfs.c
index 63b82abf3..d9c79663b 100644
--- a/grub-core/fs/zfs/zfs.c
+++ b/grub-core/fs/zfs/zfs.c
@@ -3156,7 +3156,7 @@ get_filesystem_dnode (dnode_end_t * mosmdn, char *fsname,
 static grub_err_t
 make_mdn (dnode_end_t * mdn, struct grub_zfs_data *data)
 {
-  void *osp;
+  objset_phys_t *osp;
   blkptr_t *bp;
   grub_size_t ospsize = 0;
   grub_err_t err;
@@ -3164,7 +3164,7 @@ make_mdn (dnode_end_t * mdn, struct grub_zfs_data *data)
   grub_dprintf ("zfs", "endian = %d\n", mdn->endian);
 
   bp = &(((dsl_dataset_phys_t *) DN_BONUS (&mdn->dn))->ds_bp);
-  err = zio_read (bp, mdn->endian, &osp, &ospsize, data);
+  err = zio_read (bp, mdn->endian, (void **) &osp, &ospsize, data);
   if (err)
     return err;
   if (ospsize < OBJSET_PHYS_SIZE_V14)
@@ -3175,7 +3175,7 @@ make_mdn (dnode_end_t * mdn, struct grub_zfs_data *data)
 
   mdn->endian = (grub_zfs_to_cpu64 (bp->blk_prop, mdn->endian)>>63) & 1;
   grub_memmove ((char *) &(mdn->dn),
-		(char *) &((objset_phys_t *) osp)->os_meta_dnode, DNODE_SIZE);
+		(char *) &(osp)->os_meta_dnode, DNODE_SIZE);
   grub_free (osp);
   return GRUB_ERR_NONE;
 }
-- 
2.31.1

[PATCH 2/2] fs/zfs/zfs.c: zfs_mount() - avoid pointer downcasting

[Jagannathan Raman]

Coverity reports that while loopis in the following functions uses
tainted data as boundary:
  zfs_mount() -> check_mos_features() -> dnode_get() -> zfs_log2()
  zfs_mount() -> grub_memmove()

The defect type is "Untrusted loop bound" caused as a result of
"tainted_data_downcast". Coverity does not like the pointer downcast
here and we need to address it.

We believe Coverity flags pointer downcast for the following two
reasons:
1. External data: The pointer downcast could indicate that the source is
  external data, which we need to further sanitize - such as verifying its
  limits. In this case, the data is read from an external source, which is
  a disk. But, zio_read(), which reads the data from the disk, sanitizes it
  using a checksum. checksum is the best facility that ZFS offers to verify
  external data, and we don't believe a better way exists. Therefore, no
  further action is possible for this.

2. Corruption due to alignment: downcasting a pointer from a strict type
  to less strict type could result in data corruption. For example, the
  following cast would corrupt because uint32_t is 4-byte aligned, and
  won't be able to point to 0x1003 which is not 4-byte aligned.
    uint8_t *ptr = 0x1003;
    uint32_t *word = ptr; (incorrect, alignment issues)

  This patch converts the "osp" pointer in zfs_mount() from a "void" type
  to "objset_phys_t" type to address this issue.

We are not sure if there are any other reasons why Coverity flags the
downcast. However, the fix for alignment issue masks/suppresses any
other issues from showing up.

Fixes: CID 314023

Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
---
 grub-core/fs/zfs/zfs.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/grub-core/fs/zfs/zfs.c b/grub-core/fs/zfs/zfs.c
index d9c79663b..ffa0e5863 100644
--- a/grub-core/fs/zfs/zfs.c
+++ b/grub-core/fs/zfs/zfs.c
@@ -3643,7 +3643,7 @@ zfs_mount (grub_device_t dev)
 {
   struct grub_zfs_data *data = 0;
   grub_err_t err;
-  void *osp = 0;
+  objset_phys_t *osp = 0;
   grub_size_t ospsize;
   grub_zfs_endian_t ub_endian = GRUB_ZFS_UNKNOWN_ENDIAN;
   uberblock_t *ub;
@@ -3681,7 +3681,7 @@ zfs_mount (grub_device_t dev)
 	       ? GRUB_ZFS_LITTLE_ENDIAN : GRUB_ZFS_BIG_ENDIAN);
 
   err = zio_read (&ub->ub_rootbp, ub_endian,
-		  &osp, &ospsize, data);
+		  (void **) &osp, &ospsize, data);
   if (err)
     {
       zfs_unmount (data);
@@ -3697,8 +3697,7 @@ zfs_mount (grub_device_t dev)
     }
 
   if (ub->ub_version >= SPA_VERSION_FEATURES &&
-      check_mos_features(&((objset_phys_t *) osp)->os_meta_dnode,ub_endian,
-			 data) != 0)
+      check_mos_features(&osp->os_meta_dnode, ub_endian, data) != 0)
     {
       grub_error (GRUB_ERR_BAD_FS, "Unsupported features in pool");
       grub_free (osp);
@@ -3707,8 +3706,7 @@ zfs_mount (grub_device_t dev)
     }
 
   /* Got the MOS. Save it at the memory addr MOS. */
-  grub_memmove (&(data->mos.dn), &((objset_phys_t *) osp)->os_meta_dnode,
-		DNODE_SIZE);
+  grub_memmove (&(data->mos.dn), &osp->os_meta_dnode, DNODE_SIZE);
   data->mos.endian = (grub_zfs_to_cpu64 (ub->ub_rootbp.blk_prop,
 					 ub_endian) >> 63) & 1;
   grub_free (osp);
-- 
2.31.1

Re: GRUB coverity fixes for CIDs 314020 and 314023

[Darren Kenny]

On Thursday, 2022-06-02 at 15:18:25 UTC, Jagannathan Raman wrote:
> Hi,
>
> This series addresses a couple of untrusted loop bounds flagged by
> Coverity in "grub-core/fs/zfs". Both the bugs addressed in this series
> are of the same type - caused by downcast of pointer from a strict type
> to a less strict type.
>
> Please share your thoughts on this.
>

These changes look good to me, thanks for looking at them Jag.

Reviewed-by: Darren Kenny <darren.kenny@oracle.com>

Thanks,

Darren.

> Thank you!
> --
> Jag
>
> Jagannathan Raman (2):
>   fs/zfs/zfs.c: make_mdn() - avoid pointer downcasting
>   fs/zfs/zfs.c: zfs_mount() - avoid pointer downcasting
>
>  grub-core/fs/zfs/zfs.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
>
> -- 
> 2.31.1

Re: GRUB coverity fixes for CIDs 314020 and 314023

[Daniel Kiper]

On Fri, Jun 03, 2022 at 02:12:00PM +0100, Darren Kenny wrote:
> On Thursday, 2022-06-02 at 15:18:25 UTC, Jagannathan Raman wrote:
> > Hi,
> >
> > This series addresses a couple of untrusted loop bounds flagged by
> > Coverity in "grub-core/fs/zfs". Both the bugs addressed in this series
> > are of the same type - caused by downcast of pointer from a strict type
> > to a less strict type.
> >
> > Please share your thoughts on this.
> >
>
> These changes look good to me, thanks for looking at them Jag.
>
> Reviewed-by: Darren Kenny <darren.kenny@oracle.com>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Daniel