On Tue 15-08-23 15:08:08, Baokun Li wrote: > 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 <yikebaer61@xxxxxxxxx> > Closes: https://lore.kernel.org/lkml/CALcu4raD4h9coiyEBL4Bm0zjDwxC2CyPiTwsP3zFuhot6y9Beg@xxxxxxxxxxxxxx > Fixes: 2a69c450083d ("ext4: using nofail preallocation in ext4_es_insert_extent()") > Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx> Looks good. Feel free to add: Reviewed-by: Jan Kara <jack@xxxxxxx> Honza > --- > fs/ext4/extents_status.c | 44 +++++++++++++++++++++++++++------------- > 1 file changed, 30 insertions(+), 14 deletions(-) > > 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 @@ void ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk, > 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 @@ void ext4_es_remove_extent(struct inode *inode, ext4_lblk_t lblk, > */ > 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 @@ void ext4_es_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk, > 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) > -- > 2.31.1 > -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
