CVE-2024-39276 Information

Jun 26, 2024 cve

Description

In the Linux kernel the following vulnerability has been resolved:

ext4: fix mb_cache_entry’s e_refcnt leak in ext4_xattr_block_cache_find()

Syzbot reports a warning as follows:

============================================ WARNING: CPU: 0 PID: 5075 at fs/mbcache.c:419 mb_cache_destroy+0x224/0x290 Modules linked in: CPU: 0 PID: 5075 Comm: syz-executor199 Not tainted 6.9.0-rc6-gb947cc5bf6d7 RIP: 0010:mb_cache_destroy+0x224/0x290 fs/mbcache.c:419 Call Trace: ext4_put_super+0x6d4/0xcd0 fs/ext4/super.c:1375 generic_shutdown_super+0x136/0x2d0 fs/super.c:641 kill_block_super+0x44/0x90 fs/super.c:1675 ext4_kill_sb+0x68/0xa0 fs/ext4/super.c:7327 […]

This is because when finding an entry in ext4_xattr_block_cache_find() if ext4_sb_bread() returns -ENOMEM the ce’s e_refcnt which has already grown in the __entry_find() won’t be put away and eventually trigger the above issue in mb_cache_destroy() due to reference count leakage.

So call mb_cache_entry_put() on the -ENOMEM error branch as a quick fix.

Reference

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