In the Linux kernel, the following vulnerability has been resolved:

ext4: aovid use-after-free in ext4extinsert_extent()

As Ojaswin mentioned in Link, in ext4extinsertextent(), if the path is reallocated in ext4extcreatenew_leaf(), we'll use the stale path and cause UAF. Below is a sample trace with dummy values:

ext4extinsertextent path = *ppath = 2000 ext4extcreatenewleaf(ppath) ext4findextent(ppath) path = *ppath = 2000 if (depth > path[0].pmaxdepth) kfree(path = 2000); *ppath = path = NULL; path = kcalloc() = 3000 ppath = 3000; return path; / here path is still 2000, UAF! */ eh = path[depth].p_hdr

================================================================== BUG: KASAN: slab-use-after-free in ext4extinsertextent+0x26d4/0x3330 Read of size 8 at addr ffff8881027bf7d0 by task kworker/u36:1/179 CPU: 3 UID: 0 PID: 179 Comm: kworker/u6:1 Not tainted 6.11.0-rc2-dirty #866 Call Trace: <TASK> ext4extinsertextent+0x26d4/0x3330 ext4extmapblocks+0xe22/0x2d40 ext4mapblocks+0x71e/0x1700 ext4do_writepages+0x1290/0x2800 [...]

Allocated by task 179: ext4findextent+0x81c/0x1f70 ext4extmapblocks+0x146/0x2d40 ext4mapblocks+0x71e/0x1700 ext4dowritepages+0x1290/0x2800 ext4writepages+0x26d/0x4e0 do_writepages+0x175/0x700 [...]

Freed by task 179: kfree+0xcb/0x240 ext4findextent+0x7c0/0x1f70 ext4extinsertextent+0xa26/0x3330 ext4extmapblocks+0xe22/0x2d40 ext4mapblocks+0x71e/0x1700 ext4dowritepages+0x1290/0x2800 ext4writepages+0x26d/0x4e0 dowritepages+0x175/0x700

[...]

So use *ppath to update the path to avoid the above problem.