Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

udf: validate sparing table length as an entry count, not a byte count

udf_load_sparable_map() accepts a sparing table when

sizeof(*st) + le16_to_cpu(st->reallocationTableLen) > sb->s_blocksize

is false, i.e. it treats reallocationTableLen as a number of BYTES that must fit in the block. But the table is walked as an array of 8-byte sparingEntry elements:

for (i = 0; i < le16_to_cpu(st->reallocationTableLen); i++) { struct sparingEntry *entry = &st->mapEntry[i]; ... entry->origLocation ... }

in udf_get_pblock_spar15() and udf_relocate_blocks(). A reallocationTableLen of N therefore passes the check whenever sizeof(*st) + N <= blocksize, yet the consumers index sizeof(*st) + N * sizeof(struct sparingEntry) bytes -- up to ~8x the block. On a crafted UDF image this is an out-of-bounds read in udf_get_pblock_spar15(); udf_relocate_blocks() additionally feeds the same length to udf_update_tag(), whose crc_itu_t() reads far past the block, and its memmove() through st->mapEntry[] is an out-of-bounds write.

Validate reallocationTableLen as the entry count it is, with struct_size().