From: Baokun Li <libaokun1@xxxxxxxxxx> In ext4_mb_init(), ext4_mb_avg_fragment_size_destroy() may be called when sbi->s_mb_avg_fragment_size remains uninitialized (e.g., if groupinfo slab cache allocation fails). Since ext4_mb_avg_fragment_size_destroy() lacks null pointer checking, this leads to a null pointer dereference. ================================================================== EXT4-fs: no memory for groupinfo slab cache BUG: kernel NULL pointer dereference, address: 0000000000000000 PGD 0 P4D 0 Oops: Oops: 0002 [#1] SMP PTI CPU:2 UID: 0 PID: 87 Comm:mount Not tainted 6.17.0-rc2 #1134 PREEMPT(none) RIP: 0010:_raw_spin_lock_irqsave+0x1b/0x40 Call Trace: <TASK> xa_destroy+0x61/0x130 ext4_mb_init+0x483/0x540 __ext4_fill_super+0x116d/0x17b0 ext4_fill_super+0xd3/0x280 get_tree_bdev_flags+0x132/0x1d0 vfs_get_tree+0x29/0xd0 do_new_mount+0x197/0x300 __x64_sys_mount+0x116/0x150 do_syscall_64+0x50/0x1c0 entry_SYSCALL_64_after_hwframe+0x76/0x7e ================================================================== Therefore, add necessary null check to ext4_mb_avg_fragment_size_destroy() to prevent this issue. The same fix is also applied to ext4_mb_largest_free_orders_destroy(). Reported-by: syzbot+1713b1aa266195b916c2@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://syzkaller.appspot.com/bug?extid=1713b1aa266195b916c2 Fixes: f7eaacbb4e54 ("ext4: convert free groups order lists to xarrays") Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx> --- fs/ext4/mballoc.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 5898d92ba19f..6070d3c86678 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -3655,16 +3655,26 @@ static void ext4_discard_work(struct work_struct *work) static inline void ext4_mb_avg_fragment_size_destroy(struct ext4_sb_info *sbi) { + if (!sbi->s_mb_avg_fragment_size) + return; + for (int i = 0; i < MB_NUM_ORDERS(sbi->s_sb); i++) xa_destroy(&sbi->s_mb_avg_fragment_size[i]); + kfree(sbi->s_mb_avg_fragment_size); + sbi->s_mb_avg_fragment_size = NULL; } static inline void ext4_mb_largest_free_orders_destroy(struct ext4_sb_info *sbi) { + if (!sbi->s_mb_largest_free_orders) + return; + for (int i = 0; i < MB_NUM_ORDERS(sbi->s_sb); i++) xa_destroy(&sbi->s_mb_largest_free_orders[i]); + kfree(sbi->s_mb_largest_free_orders); + sbi->s_mb_largest_free_orders = NULL; } int ext4_mb_init(struct super_block *sb) -- 2.46.1
