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fs/hfsplus: Don't use uninitialized data on corrupt filesystems

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Valgrind identified the following use of uninitialized data:

  ==2782220== Conditional jump or move depends on uninitialised value(s)
  ==2782220==    at 0x42B364: grub_hfsplus_btree_search (hfsplus.c:566)
  ==2782220==    by 0x42B21D: grub_hfsplus_read_block (hfsplus.c:185)
  ==2782220==    by 0x42A693: grub_fshelp_read_file (fshelp.c:386)
  ==2782220==    by 0x42C598: grub_hfsplus_read_file (hfsplus.c:219)
  ==2782220==    by 0x42C598: grub_hfsplus_mount (hfsplus.c:330)
  ==2782220==    by 0x42B8C5: grub_hfsplus_dir (hfsplus.c:958)
  ==2782220==    by 0x4C1AE6: grub_fs_probe (fs.c:73)
  ==2782220==    by 0x407C94: grub_ls_list_files (ls.c:186)
  ==2782220==    by 0x407C94: grub_cmd_ls (ls.c:284)
  ==2782220==    by 0x4D7130: grub_extcmd_dispatcher (extcmd.c:55)
  ==2782220==    by 0x4045A6: execute_command (grub-fstest.c:59)
  ==2782220==    by 0x4045A6: fstest (grub-fstest.c:433)
  ==2782220==    by 0x4045A6: main (grub-fstest.c:772)
  ==2782220==  Uninitialised value was created by a heap allocation
  ==2782220==    at 0x483C7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
  ==2782220==    by 0x4C0305: grub_malloc (mm.c:42)
  ==2782220==    by 0x42C21D: grub_hfsplus_mount (hfsplus.c:239)
  ==2782220==    by 0x42B8C5: grub_hfsplus_dir (hfsplus.c:958)
  ==2782220==    by 0x4C1AE6: grub_fs_probe (fs.c:73)
  ==2782220==    by 0x407C94: grub_ls_list_files (ls.c:186)
  ==2782220==    by 0x407C94: grub_cmd_ls (ls.c:284)
  ==2782220==    by 0x4D7130: grub_extcmd_dispatcher (extcmd.c:55)
  ==2782220==    by 0x4045A6: execute_command (grub-fstest.c:59)
  ==2782220==    by 0x4045A6: fstest (grub-fstest.c:433)
  ==2782220==    by 0x4045A6: main (grub-fstest.c:772)

This happens when the process of reading the catalog file goes sufficiently
wrong that there's an attempt to read the extent overflow file, which has
not yet been loaded. Keep track of when the extent overflow file is
fully loaded and refuse to use it before then.

The load valgrind doesn't like is btree->nodesize, and that's then used
to allocate a data structure. It looks like there are subsequently a lot
of reads based on that pointer so OOB reads are likely, and indeed crashes
(albeit difficult-to-replicate ones) have been observed in fuzzing.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This commit is contained in:
Daniel Axtens 2021-02-02 16:59:35 +11:00 committed by Daniel Kiper
parent 58ea11d5b9
commit 2ca0e5dbcd
2 changed files with 16 additions and 0 deletions
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14
grub-core/fs/hfsplus.c
View File

@ -177,6 +177,17 @@ grub_hfsplus_read_block (grub_fshelp_node_t node, grub_disk_addr_t fileblock)
break;
}
/*
* If the extent overflow tree isn't ready yet, we can't look
* in it. This can happen where the catalog file is corrupted.
*/
if (!node->data->extoverflow_tree_ready)
{
grub_error (GRUB_ERR_BAD_FS,
"attempted to read extent overflow tree before loading");
break;
}
/* Set up the key to look for in the extent overflow file. */
extoverflow.extkey.fileid = node->fileid;
extoverflow.extkey.type = 0;
@ -241,6 +252,7 @@ grub_hfsplus_mount (grub_disk_t disk)
return 0;
data->disk = disk;
data->extoverflow_tree_ready = 0;
/* Read the bootblock. */
grub_disk_read (disk, GRUB_HFSPLUS_SBLOCK, 0, sizeof (volheader),
@ -357,6 +369,8 @@ grub_hfsplus_mount (grub_disk_t disk)
if (data->extoverflow_tree.nodesize < 2)
goto fail;
data->extoverflow_tree_ready = 1;
if (grub_hfsplus_read_file (&data->attr_tree.file, 0, 0,
sizeof (struct grub_hfsplus_btnode),
sizeof (header), (char *) &header) <= 0)

2
include/grub/hfsplus.h
View File

@ -113,6 +113,8 @@ struct grub_hfsplus_data
struct grub_hfsplus_btree extoverflow_tree;
struct grub_hfsplus_btree attr_tree;
int extoverflow_tree_ready;
struct grub_hfsplus_file dirroot;
struct grub_hfsplus_file opened_file;