partitions: aix: bound the lvd scan to one sector

aix_partition() reads the logical-volume descriptor array as a single
sector and then scans it:

	if (numlvs && (d = read_part_sector(state, vgda_sector + 1, &sect))) {
		struct lvd *p = (struct lvd *)d;
		...
		for (i = 0; foundlvs < numlvs && i < state->limit; i++) {
			lvip[i].pps_per_lv = be16_to_cpu(p[i].num_lps);

p points at a single 512-byte sector, which holds SECTOR_SIZE /
sizeof(struct lvd) = 16 entries, but the loop runs until foundlvs reaches
the on-disk numlvs or i reaches state->limit (DISK_MAX_PARTS, 256).
numlvs is an on-disk __be16 read straight from the volume group
descriptor and is not validated, so a crafted AIX image with numlvs
larger than 16 and lvd entries whose num_lps fields are zero (so foundlvs
never advances) drives the loop to read p[i] well past the end of the
read sector buffer.

Commit d97a86c ("partitions: aix.c: off by one bug") hardened the
matching write of lvip[lv_ix] in 2014 but left this read loop unbounded.

Bound the scan to the number of struct lvd entries that fit in the
sector that was actually read.

Fixes: 6ceea22 ("partitions: add aix lvm partition support files")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Link: https://patch.msgid.link/20260714114806.3761553-1-michael.bommarito@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: mjbommar

block/partitions/aix.c

@@ -208,7 +208,14 @@ int aix_partition(struct parsed_partitions *state)
 		if (n) {
 			int foundlvs = 0;
 
-			for (i = 0; foundlvs < numlvs && i < state->limit; i += 1) {
+			/*
+			 * The lvd array was read as a single sector; only the
+			 * struct lvd entries that fit in it are valid.  Bound the
+			 * scan so an on-disk numlvs larger than that cannot walk
+			 * the read buffer out of bounds.
+			 */
+			for (i = 0; foundlvs < numlvs && i < state->limit &&
+				    i < SECTOR_SIZE / (int)sizeof(struct lvd); i++) {
 				lvip[i].pps_per_lv = be16_to_cpu(p[i].num_lps);
 				if (lvip[i].pps_per_lv)
 					foundlvs += 1;