From d30e87ea49b2dc1dc6277ca447b0aaac03f49cde Mon Sep 17 00:00:00 2001 From: Luca Boccassi Date: Wed, 24 Jun 2026 13:56:37 +0100 Subject: [PATCH] uid-range: fix out-of-bounds write in uid_range_partition() uid_range_partition() filled the grown entries[] buffer backwards in place. The backward-fill invariant (the write cursor stays above the read index) only holds when every source entry contributes at least one partition; an entry with nr < size contributes zero, so the cursor stalls while the read index keeps descending. A later multi-part entry's writes then overwrite the still-live zero-part slot, the corrupted slot is re-read as a one-part entry, and the next range->entries[--t] underflows. Add a forward compaction first pass that drops the zero-part entries before the backward fill. Follow-up for 025439faaa8c053fab9fd01fb5f45fb819408bc5 Co-Authored-by: Paul Meyer --- src/basic/uid-range.c | 13 ++++++-- src/test/test-uid-range.c | 62 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 73 insertions(+), 2 deletions(-) diff --git a/src/basic/uid-range.c b/src/basic/uid-range.c index 62c7d7d928e..e9e8932f389 100644 --- a/src/basic/uid-range.c +++ b/src/basic/uid-range.c @@ -395,9 +395,18 @@ int uid_range_partition(UIDRange *range, uid_t size) { if (n_new_entries > range->n_entries && !GREEDY_REALLOC(range->entries, n_new_entries)) return -ENOMEM; - /* Work backwards to avoid overwriting entries we still need to read */ + /* Compact in place: drop entries that contribute zero partitions (nr < size). This forward pass + * reads each entry once and only writes to lower-or-equal indices, so it cannot alias an unread + * source entry. */ + size_t n_src = 0; + for (size_t i = 0; i < range->n_entries; i++) + if (range->entries[i].nr >= size) + range->entries[n_src++] = range->entries[i]; + + /* Pre-compaction guarantees every surviving entry contributes at least one partition slot, so the + * write cursor t stays ahead of the read index. */ size_t t = n_new_entries; - for (size_t i = range->n_entries; i > 0; i--) { + for (size_t i = n_src; i > 0; i--) { UIDRangeEntry *e = range->entries + i - 1; unsigned n_parts = e->nr / size; diff --git a/src/test/test-uid-range.c b/src/test/test-uid-range.c index 6eef98153ef..fdcbd8896e8 100644 --- a/src/test/test-uid-range.c +++ b/src/test/test-uid-range.c @@ -318,6 +318,68 @@ TEST(uid_range_partition) { p = uid_range_free(p); + /* Small entry preceding a large entry: the small entry must be dropped and the large entry + * partitioned without the in-place backward-fill write cursor aliasing the still-live small entry + * slot. */ + ASSERT_OK(uid_range_add_str(&p, "0-4")); + ASSERT_OK(uid_range_add_str(&p, "100-129")); + ASSERT_EQ(uid_range_entries(p), 2U); + ASSERT_OK(uid_range_partition(p, 10)); + ASSERT_EQ(uid_range_entries(p), 3U); + ASSERT_EQ(p->entries[0].start, 100U); + ASSERT_EQ(p->entries[0].nr, 10U); + ASSERT_EQ(p->entries[1].start, 110U); + ASSERT_EQ(p->entries[1].nr, 10U); + ASSERT_EQ(p->entries[2].start, 120U); + ASSERT_EQ(p->entries[2].nr, 10U); + + p = uid_range_free(p); + + /* A too-small entry between two partitionable entries is dropped; the others still partition. */ + ASSERT_OK(uid_range_add_str(&p, "0-4")); /* nr=5 < size -> dropped */ + ASSERT_OK(uid_range_add_str(&p, "50-69")); /* nr=20 -> 2 parts */ + ASSERT_OK(uid_range_add_str(&p, "200-204")); /* nr=5 < size -> dropped */ + ASSERT_OK(uid_range_add_str(&p, "1000-1029")); /* nr=30 -> 3 parts */ + ASSERT_EQ(uid_range_entries(p), 4U); + ASSERT_OK(uid_range_partition(p, 10)); + ASSERT_EQ(uid_range_entries(p), 5U); + ASSERT_EQ(p->entries[0].start, 50U); + ASSERT_EQ(p->entries[0].nr, 10U); + ASSERT_EQ(p->entries[1].start, 60U); + ASSERT_EQ(p->entries[1].nr, 10U); + ASSERT_EQ(p->entries[2].start, 1000U); + ASSERT_EQ(p->entries[2].nr, 10U); + ASSERT_EQ(p->entries[3].start, 1010U); + ASSERT_EQ(p->entries[3].nr, 10U); + ASSERT_EQ(p->entries[4].start, 1020U); + ASSERT_EQ(p->entries[4].nr, 10U); + + p = uid_range_free(p); + + /* A too-small entry before a partitionable entry is dropped. */ + ASSERT_OK(uid_range_add_str(&p, "0-4")); /* nr=5 < size -> dropped */ + ASSERT_OK(uid_range_add_str(&p, "100-119")); /* nr=20 -> 2 parts */ + ASSERT_OK(uid_range_partition(p, 10)); + ASSERT_EQ(uid_range_entries(p), 2U); + ASSERT_EQ(p->entries[0].start, 100U); + ASSERT_EQ(p->entries[0].nr, 10U); + ASSERT_EQ(p->entries[1].start, 110U); + ASSERT_EQ(p->entries[1].nr, 10U); + + p = uid_range_free(p); + + /* A too-small entry after a partitionable entry is dropped. */ + ASSERT_OK(uid_range_add_str(&p, "0-199")); /* nr=200 -> 2 parts */ + ASSERT_OK(uid_range_add_str(&p, "1000-1004")); /* nr=5 < size -> dropped */ + ASSERT_OK(uid_range_partition(p, 100)); + ASSERT_EQ(uid_range_entries(p), 2U); + ASSERT_EQ(p->entries[0].start, 0U); + ASSERT_EQ(p->entries[0].nr, 100U); + ASSERT_EQ(p->entries[1].start, 100U); + ASSERT_EQ(p->entries[1].nr, 100U); + + p = uid_range_free(p); + /* Partition size of 1 */ ASSERT_OK(uid_range_add_str(&p, "100-102")); ASSERT_OK(uid_range_partition(p, 1)); -- 2.47.3