Presently, a corrupted or malicious UDF filesystem containing a very large number (or cycle) of Logical Volume Integrity Descriptor extent indirections may trigger a stack overflow and kernel panic in udf_load_logicalvolint() on mount. Replace the unnecessary recursion in udf_load_logicalvolint() with simple iteration. Set an arbitrary limit of 1000 indirections (which would have almost certainly overflowed the stack without this fix), and treat such cases as if there were no LVID.
Unified · Split
| @@ -78,6 +78,15 @@ · 77 unmodified lines | ||
| 78 | 78 | #define VSD_FIRST_SECTOR_OFFSET 32768 |
| 79 | 79 | #define VSD_MAX_SECTOR_OFFSET 0x800000 |
| 80 | 80 | |
| 81 | +/* | |
| 82 | + * Maximum number of Terminating Descriptor / Logical Volume Integrity | |
| 83 | + * Descriptor redirections. The chosen numbers are arbitrary - just that we | |
| 84 | + * hopefully don't limit any real use of rewritten inode on write-once media | |
| 85 | + * but avoid looping for too long on corrupted media. | |
| 86 | + */ | |
| 87 | +#define UDF_MAX_TD_NESTING 64 | |
| 88 | +#define UDF_MAX_LVID_NESTING 1000 | |
| 89 | + | |
| 81 | 90 | enum { UDF_MAX_LINKS = 0xffff }; |
| 82 | 91 | |
| 83 | 92 | /* These are the "meat" - everything else is stuffing */ |
| @@ -1541,42 +1550,52 @@ out_bh: · 1457 unmodified lines | ||
| 1541 | 1550 | } |
| 1542 | 1551 | |
| 1543 | 1552 | /* |
| 1544 | − * udf_load_logicalvolint | |
| 1545 | − * | |
| 1553 | + * Find the prevailing Logical Volume Integrity Descriptor. | |
| 1546 | 1554 | */ |
| 1547 | 1555 | static void udf_load_logicalvolint(struct super_block *sb, struct kernel_extent_ad loc) |
| 1548 | 1556 | { |
| 1549 | − struct buffer_head *bh = NULL; | |
| 1557 | + struct buffer_head *bh, *final_bh; | |
| 1550 | 1558 | uint16_t ident; |
| 1551 | 1559 | struct udf_sb_info *sbi = UDF_SB(sb); |
| 1552 | 1560 | struct logicalVolIntegrityDesc *lvid; |
| 1561 | + int indirections = 0; | |
| 1562 | + | |
| 1563 | + while (++indirections <= UDF_MAX_LVID_NESTING) { | |
| 1564 | + final_bh = NULL; | |
| 1565 | + while (loc.extLength > 0 && | |
| 1566 | + (bh = udf_read_tagged(sb, loc.extLocation, | |
| 1567 | + loc.extLocation, &ident))) { | |
| 1568 | + if (ident != TAG_IDENT_LVID) { | |
| 1569 | + brelse(bh); | |
| 1570 | + break; | |
| 1571 | + } | |
| 1572 | + | |
| 1573 | + brelse(final_bh); | |
| 1574 | + final_bh = bh; | |
| 1553 | 1575 | |
| 1554 | − while (loc.extLength > 0 && | |
| 1555 | − (bh = udf_read_tagged(sb, loc.extLocation, | |
| 1556 | − loc.extLocation, &ident)) && | |
| 1557 | − ident == TAG_IDENT_LVID) { | |
| 1558 | − sbi->s_lvid_bh = bh; | |
| 1559 | − lvid = (struct logicalVolIntegrityDesc *)bh->b_data; | |
| 1576 | + loc.extLength -= sb->s_blocksize; | |
| 1577 | + loc.extLocation++; | |
| 1578 | + } | |
| 1560 | 1579 | |
| 1561 | − if (lvid->nextIntegrityExt.extLength) | |
| 1562 | − udf_load_logicalvolint(sb, | |
| 1563 | − leea_to_cpu(lvid->nextIntegrityExt)); | |
| 1580 | + if (!final_bh) | |
| 1581 | + return; | |
| 1564 | 1582 | |
| 1565 | − if (sbi->s_lvid_bh != bh) | |
| 1566 | − brelse(bh); | |
| 1567 | − loc.extLength -= sb->s_blocksize; | |
| 1568 | − loc.extLocation++; | |
| 1583 | + brelse(sbi->s_lvid_bh); | |
| 1584 | + sbi->s_lvid_bh = final_bh; | |
| 1585 | + | |
| 1586 | + lvid = (struct logicalVolIntegrityDesc *)final_bh->b_data; | |
| 1587 | + if (lvid->nextIntegrityExt.extLength == 0) | |
| 1588 | + return; | |
| 1589 | + | |
| 1590 | + loc = leea_to_cpu(lvid->nextIntegrityExt); | |
| 1569 | 1591 | } |
| 1570 | − if (sbi->s_lvid_bh != bh) | |
| 1571 | − brelse(bh); | |
| 1592 | + | |
| 1593 | + udf_warn(sb, "Too many LVID indirections (max %u), ignoring.\n", | |
| 1594 | + UDF_MAX_LVID_NESTING); | |
| 1595 | + brelse(sbi->s_lvid_bh); | |
| 1596 | + sbi->s_lvid_bh = NULL; | |
| 1572 | 1597 | } |
| 1573 | 1598 | |
| 1574 | −/* | |
| 1575 | − * Maximum number of Terminating Descriptor redirections. The chosen number is | |
| 1576 | − * arbitrary - just that we hopefully don't limit any real use of rewritten | |
| 1577 | − * inode on write-once media but avoid looping for too long on corrupted media. | |
| 1578 | − */ | |
| 1579 | −#define UDF_MAX_TD_NESTING 64 | |
| 1580 | 1599 | |
| 1581 | 1600 | /* |
| 1582 | 1601 | * Process a main/reserve volume descriptor sequence. |