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

ext4: update origpath in ext4find_extent()

In ext4findextent(), if the path is not big enough, we free it and set *origpath to NULL. But after reallocating and successfully initializing the path, we don't update *origpath, in which case the caller gets a valid path but a NULL ppath, and this may cause a NULL pointer dereference or a path memory leak. For example:

ext4splitextent path = *ppath = 2000 ext4findextent if (depth > path[0].pmaxdepth) kfree(path = 2000); *origpath = path = NULL; path = kcalloc() = 3000 ext4splitextentat(*ppath = NULL) path = *ppath; ex = path[depth].pext; // NULL pointer dereference!

================================================================== BUG: kernel NULL pointer dereference, address: 0000000000000010 CPU: 6 UID: 0 PID: 576 Comm: fsstress Not tainted 6.11.0-rc2-dirty #847 RIP: 0010:ext4splitextentat+0x6d/0x560 Call Trace: <TASK> ext4splitextent.isra.0+0xcb/0x1b0 ext4extconverttoinitialized+0x168/0x6c0 ext4exthandleunwrittenextents+0x325/0x4d0 ext4extmapblocks+0x520/0xdb0 ext4mapblocks+0x2b0/0x690 ext4iomapbegin+0x20e/0x2c0

[...]

Therefore, *orig_path is updated when the extent lookup succeeds, so that the caller can safely use path or *ppath.