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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: Mon, 18 Jan 2021 14:57:17 +1100
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Subject: [PATCH] fs/jfs: Limit the extents that getblk() can consider
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getblk() implicitly trusts that treehead->count is an accurate count of
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the number of extents. However, that value is read from disk and is not
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trustworthy, leading to OOB reads and crashes. I am not sure to what
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extent the data read from OOB can influence subsequent program execution.
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Require callers to pass in the maximum number of extents for which
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they have storage.
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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/jfs.c | 8 +++++---
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1 file changed, 5 insertions(+), 3 deletions(-)
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diff --git a/grub-core/fs/jfs.c b/grub-core/fs/jfs.c
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index 1819899bd..6e81f37da 100644
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--- a/grub-core/fs/jfs.c
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+++ b/grub-core/fs/jfs.c
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@@ -261,13 +261,15 @@ static grub_err_t grub_jfs_lookup_symlink (struct grub_jfs_data *data, grub_uint
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static grub_int64_t
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getblk (struct grub_jfs_treehead *treehead,
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struct grub_jfs_tree_extent *extents,
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+ int max_extents,
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struct grub_jfs_data *data,
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grub_uint64_t blk)
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{
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int found = -1;
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int i;
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- for (i = 0; i < grub_le_to_cpu16 (treehead->count) - 2; i++)
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+ for (i = 0; i < grub_le_to_cpu16 (treehead->count) - 2 &&
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+ i < max_extents; i++)
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{
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if (treehead->flags & GRUB_JFS_TREE_LEAF)
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{
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@@ -302,7 +304,7 @@ getblk (struct grub_jfs_treehead *treehead,
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<< (grub_le_to_cpu16 (data->sblock.log2_blksz)
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- GRUB_DISK_SECTOR_BITS), 0,
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sizeof (*tree), (char *) tree))
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- ret = getblk (&tree->treehead, &tree->extents[0], data, blk);
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+ ret = getblk (&tree->treehead, &tree->extents[0], 254, data, blk);
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grub_free (tree);
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return ret;
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}
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@@ -316,7 +318,7 @@ static grub_int64_t
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grub_jfs_blkno (struct grub_jfs_data *data, struct grub_jfs_inode *inode,
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grub_uint64_t blk)
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{
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- return getblk (&inode->file.tree, &inode->file.extents[0], data, blk);
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+ return getblk (&inode->file.tree, &inode->file.extents[0], 16, data, blk);
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}
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