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

commit 3ec997bd55 upstream.

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().

Fixes: 1df2ae31c7 ("udf: Fortify loading of sparing table")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Link: https://patch.msgid.link/20260612-b4-disp-91780c4e-v1-1-f15112ff6882@proton.me
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/udf/super.c

@@ -1395,7 +1395,8 @@ static int udf_load_sparable_map(struct super_block *sb,
 		if (ident != 0 ||
 		    strncmp(st->sparingIdent.ident, UDF_ID_SPARING,
 			    strlen(UDF_ID_SPARING)) ||
-		    sizeof(*st) + le16_to_cpu(st->reallocationTableLen) >
+		    struct_size(st, mapEntry,
+				le16_to_cpu(st->reallocationTableLen)) >
 							sb->s_blocksize) {
 			brelse(bh);
 			continue;