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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Daniel Axtens <dja@axtens.net>
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Date: Tue, 2 Feb 2021 16:59:35 +1100
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Subject: [PATCH] fs/hfsplus: Don't use uninitialized data on corrupt
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filesystems
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Valgrind identified the following use of uninitialized data:
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==2782220== Conditional jump or move depends on uninitialised value(s)
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==2782220== at 0x42B364: grub_hfsplus_btree_search (hfsplus.c:566)
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==2782220== by 0x42B21D: grub_hfsplus_read_block (hfsplus.c:185)
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==2782220== by 0x42A693: grub_fshelp_read_file (fshelp.c:386)
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==2782220== by 0x42C598: grub_hfsplus_read_file (hfsplus.c:219)
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==2782220== by 0x42C598: grub_hfsplus_mount (hfsplus.c:330)
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==2782220== by 0x42B8C5: grub_hfsplus_dir (hfsplus.c:958)
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==2782220== by 0x4C1AE6: grub_fs_probe (fs.c:73)
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==2782220== by 0x407C94: grub_ls_list_files (ls.c:186)
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==2782220== by 0x407C94: grub_cmd_ls (ls.c:284)
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==2782220== by 0x4D7130: grub_extcmd_dispatcher (extcmd.c:55)
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==2782220== by 0x4045A6: execute_command (grub-fstest.c:59)
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==2782220== by 0x4045A6: fstest (grub-fstest.c:433)
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==2782220== by 0x4045A6: main (grub-fstest.c:772)
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==2782220== Uninitialised value was created by a heap allocation
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==2782220== at 0x483C7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
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==2782220== by 0x4C0305: grub_malloc (mm.c:42)
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==2782220== by 0x42C21D: grub_hfsplus_mount (hfsplus.c:239)
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==2782220== by 0x42B8C5: grub_hfsplus_dir (hfsplus.c:958)
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==2782220== by 0x4C1AE6: grub_fs_probe (fs.c:73)
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==2782220== by 0x407C94: grub_ls_list_files (ls.c:186)
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==2782220== by 0x407C94: grub_cmd_ls (ls.c:284)
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==2782220== by 0x4D7130: grub_extcmd_dispatcher (extcmd.c:55)
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==2782220== by 0x4045A6: execute_command (grub-fstest.c:59)
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==2782220== by 0x4045A6: fstest (grub-fstest.c:433)
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==2782220== by 0x4045A6: main (grub-fstest.c:772)
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This happens when the process of reading the catalog file goes sufficiently
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wrong that there's an attempt to read the extent overflow file, which has
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not yet been loaded. Keep track of when the extent overflow file is
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fully loaded and refuse to use it before then.
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The load valgrind doesn't like is btree->nodesize, and that's then used
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to allocate a data structure. It looks like there are subsequently a lot
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of reads based on that pointer so OOB reads are likely, and indeed crashes
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(albeit difficult-to-replicate ones) have been observed in fuzzing.
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Signed-off-by: Daniel Axtens <dja@axtens.net>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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---
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grub-core/fs/hfsplus.c | 14 ++++++++++++++
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include/grub/hfsplus.h | 2 ++
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2 files changed, 16 insertions(+)
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diff --git a/grub-core/fs/hfsplus.c b/grub-core/fs/hfsplus.c
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index 423f4b956..8c0c80473 100644
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--- a/grub-core/fs/hfsplus.c
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+++ b/grub-core/fs/hfsplus.c
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@@ -177,6 +177,17 @@ grub_hfsplus_read_block (grub_fshelp_node_t node, grub_disk_addr_t fileblock)
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break;
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}
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+ /*
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+ * If the extent overflow tree isn't ready yet, we can't look
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+ * in it. This can happen where the catalog file is corrupted.
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+ */
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+ if (!node->data->extoverflow_tree_ready)
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+ {
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+ grub_error (GRUB_ERR_BAD_FS,
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+ "attempted to read extent overflow tree before loading");
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+ break;
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+ }
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+
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/* Set up the key to look for in the extent overflow file. */
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extoverflow.extkey.fileid = node->fileid;
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extoverflow.extkey.type = 0;
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@@ -241,6 +252,7 @@ grub_hfsplus_mount (grub_disk_t disk)
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return 0;
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data->disk = disk;
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+ data->extoverflow_tree_ready = 0;
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/* Read the bootblock. */
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grub_disk_read (disk, GRUB_HFSPLUS_SBLOCK, 0, sizeof (volheader),
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@@ -357,6 +369,8 @@ grub_hfsplus_mount (grub_disk_t disk)
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if (data->extoverflow_tree.nodesize < 2)
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goto fail;
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+ data->extoverflow_tree_ready = 1;
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+
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if (grub_hfsplus_read_file (&data->attr_tree.file, 0, 0,
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sizeof (struct grub_hfsplus_btnode),
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sizeof (header), (char *) &header) <= 0)
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diff --git a/include/grub/hfsplus.h b/include/grub/hfsplus.h
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index 117740ae2..e14dd31ff 100644
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--- a/include/grub/hfsplus.h
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+++ b/include/grub/hfsplus.h
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@@ -113,6 +113,8 @@ struct grub_hfsplus_data
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struct grub_hfsplus_btree extoverflow_tree;
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struct grub_hfsplus_btree attr_tree;
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+ int extoverflow_tree_ready;
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+
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struct grub_hfsplus_file dirroot;
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struct grub_hfsplus_file opened_file;
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