From 768d612f79822d30a1e7d132a4d4b05337ce42ec Mon Sep 17 00:00:00 2001 From: Baokun Li Date: Tue, 15 Aug 2023 15:08:08 +0800 Subject: ext4: fix slab-use-after-free in ext4_es_insert_extent() Yikebaer reported an issue: ================================================================== BUG: KASAN: slab-use-after-free in ext4_es_insert_extent+0xc68/0xcb0 fs/ext4/extents_status.c:894 Read of size 4 at addr ffff888112ecc1a4 by task syz-executor/8438 CPU: 1 PID: 8438 Comm: syz-executor Not tainted 6.5.0-rc5 #1 Call Trace: [...] kasan_report+0xba/0xf0 mm/kasan/report.c:588 ext4_es_insert_extent+0xc68/0xcb0 fs/ext4/extents_status.c:894 ext4_map_blocks+0x92a/0x16f0 fs/ext4/inode.c:680 ext4_alloc_file_blocks.isra.0+0x2df/0xb70 fs/ext4/extents.c:4462 ext4_zero_range fs/ext4/extents.c:4622 [inline] ext4_fallocate+0x251c/0x3ce0 fs/ext4/extents.c:4721 [...] Allocated by task 8438: [...] kmem_cache_zalloc include/linux/slab.h:693 [inline] __es_alloc_extent fs/ext4/extents_status.c:469 [inline] ext4_es_insert_extent+0x672/0xcb0 fs/ext4/extents_status.c:873 ext4_map_blocks+0x92a/0x16f0 fs/ext4/inode.c:680 ext4_alloc_file_blocks.isra.0+0x2df/0xb70 fs/ext4/extents.c:4462 ext4_zero_range fs/ext4/extents.c:4622 [inline] ext4_fallocate+0x251c/0x3ce0 fs/ext4/extents.c:4721 [...] Freed by task 8438: [...] kmem_cache_free+0xec/0x490 mm/slub.c:3823 ext4_es_try_to_merge_right fs/ext4/extents_status.c:593 [inline] __es_insert_extent+0x9f4/0x1440 fs/ext4/extents_status.c:802 ext4_es_insert_extent+0x2ca/0xcb0 fs/ext4/extents_status.c:882 ext4_map_blocks+0x92a/0x16f0 fs/ext4/inode.c:680 ext4_alloc_file_blocks.isra.0+0x2df/0xb70 fs/ext4/extents.c:4462 ext4_zero_range fs/ext4/extents.c:4622 [inline] ext4_fallocate+0x251c/0x3ce0 fs/ext4/extents.c:4721 [...] ================================================================== The flow of issue triggering is as follows: 1. remove es raw es es removed es1 |-------------------| -> |----|.......|------| 2. insert es es insert es1 merge with es es1 merge with es and free es1 |----|.......|------| -> |------------|------| -> |-------------------| es merges with newes, then merges with es1, frees es1, then determines if es1->es_len is 0 and triggers a UAF. The code flow is as follows: ext4_es_insert_extent es1 = __es_alloc_extent(true); es2 = __es_alloc_extent(true); __es_remove_extent(inode, lblk, end, NULL, es1) __es_insert_extent(inode, &newes, es1) ---> insert es1 to es tree __es_insert_extent(inode, &newes, es2) ext4_es_try_to_merge_right ext4_es_free_extent(inode, es1) ---> es1 is freed if (es1 && !es1->es_len) // Trigger UAF by determining if es1 is used. We determine whether es1 or es2 is used immediately after calling __es_remove_extent() or __es_insert_extent() to avoid triggering a UAF if es1 or es2 is freed. Reported-by: Yikebaer Aizezi Closes: https://lore.kernel.org/lkml/CALcu4raD4h9coiyEBL4Bm0zjDwxC2CyPiTwsP3zFuhot6y9Beg@mail.gmail.com Fixes: 2a69c450083d ("ext4: using nofail preallocation in ext4_es_insert_extent()") Cc: stable@kernel.org Signed-off-by: Baokun Li Reviewed-by: Jan Kara Link: https://lore.kernel.org/r/20230815070808.3377171-1-libaokun1@huawei.com Signed-off-by: Theodore Ts'o --- fs/ext4/extents_status.c | 44 ++++++++++++++++++++++++++++++-------------- 1 file changed, 30 insertions(+), 14 deletions(-) (limited to 'fs') diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c index 9b5b8951afb4..6f7de14c0fa8 100644 --- a/fs/ext4/extents_status.c +++ b/fs/ext4/extents_status.c @@ -878,23 +878,29 @@ retry: err1 = __es_remove_extent(inode, lblk, end, NULL, es1); if (err1 != 0) goto error; + /* Free preallocated extent if it didn't get used. */ + if (es1) { + if (!es1->es_len) + __es_free_extent(es1); + es1 = NULL; + } err2 = __es_insert_extent(inode, &newes, es2); if (err2 == -ENOMEM && !ext4_es_must_keep(&newes)) err2 = 0; if (err2 != 0) goto error; + /* Free preallocated extent if it didn't get used. */ + if (es2) { + if (!es2->es_len) + __es_free_extent(es2); + es2 = NULL; + } if (sbi->s_cluster_ratio > 1 && test_opt(inode->i_sb, DELALLOC) && (status & EXTENT_STATUS_WRITTEN || status & EXTENT_STATUS_UNWRITTEN)) __revise_pending(inode, lblk, len); - - /* es is pre-allocated but not used, free it. */ - if (es1 && !es1->es_len) - __es_free_extent(es1); - if (es2 && !es2->es_len) - __es_free_extent(es2); error: write_unlock(&EXT4_I(inode)->i_es_lock); if (err1 || err2) @@ -1491,8 +1497,12 @@ retry: */ write_lock(&EXT4_I(inode)->i_es_lock); err = __es_remove_extent(inode, lblk, end, &reserved, es); - if (es && !es->es_len) - __es_free_extent(es); + /* Free preallocated extent if it didn't get used. */ + if (es) { + if (!es->es_len) + __es_free_extent(es); + es = NULL; + } write_unlock(&EXT4_I(inode)->i_es_lock); if (err) goto retry; @@ -2047,19 +2057,25 @@ retry: err1 = __es_remove_extent(inode, lblk, lblk, NULL, es1); if (err1 != 0) goto error; + /* Free preallocated extent if it didn't get used. */ + if (es1) { + if (!es1->es_len) + __es_free_extent(es1); + es1 = NULL; + } err2 = __es_insert_extent(inode, &newes, es2); if (err2 != 0) goto error; + /* Free preallocated extent if it didn't get used. */ + if (es2) { + if (!es2->es_len) + __es_free_extent(es2); + es2 = NULL; + } if (allocated) __insert_pending(inode, lblk); - - /* es is pre-allocated but not used, free it. */ - if (es1 && !es1->es_len) - __es_free_extent(es1); - if (es2 && !es2->es_len) - __es_free_extent(es2); error: write_unlock(&EXT4_I(inode)->i_es_lock); if (err1 || err2) -- cgit