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ext4: fix potential negative array index in do_split()
If for any reason a directory passed to do_split() does not have enough active entries to exceed half the size of the block, we can end up iterating over all "count" entries without finding a split point. In this case, count == move, and split will be zero, and we will attempt a negative index into map[]. Guard against this by detecting this case, and falling back to split-to-half-of-count instead; in this case we will still have plenty of space (> half blocksize) in each split block. Fixes: ef2b02d3e617 ("ext34: ensure do_split leaves enough free space in both blocks") Signed-off-by: Eric Sandeen <sandeen@redhat.com> Reviewed-by: Andreas Dilger <adilger@dilger.ca> Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/f53e246b-647c-64bb-16ec-135383c70ad7@redhat.com Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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@ -1858,7 +1858,7 @@ static struct ext4_dir_entry_2 *do_split(handle_t *handle, struct inode *dir,
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blocksize, hinfo, map);
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map -= count;
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dx_sort_map(map, count);
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/* Split the existing block in the middle, size-wise */
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/* Ensure that neither split block is over half full */
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size = 0;
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move = 0;
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for (i = count-1; i >= 0; i--) {
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@ -1868,8 +1868,18 @@ static struct ext4_dir_entry_2 *do_split(handle_t *handle, struct inode *dir,
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size += map[i].size;
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move++;
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}
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/* map index at which we will split */
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split = count - move;
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/*
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* map index at which we will split
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*
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* If the sum of active entries didn't exceed half the block size, just
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* split it in half by count; each resulting block will have at least
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* half the space free.
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*/
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if (i > 0)
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split = count - move;
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else
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split = count/2;
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hash2 = map[split].hash;
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continued = hash2 == map[split - 1].hash;
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dxtrace(printk(KERN_INFO "Split block %lu at %x, %i/%i\n",
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