CVE-2024-49881

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

ext4: update orig_path in ext4_find_extent()

In ext4_find_extent(), if the path is not big enough, we free it and set

*orig_path to NULL. But after reallocating and successfully initializing

the path, we don't update *orig_path, 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:

ext4_split_extent

path = *ppath = 2000

ext4_find_extent

if (depth > path[0].p_maxdepth)

kfree(path = 2000);

*orig_path = path = NULL;

path = kcalloc() = 3000

ext4_split_extent_at(*ppath = NULL)

path = *ppath;

ex = path[depth].p_ext;

// 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:ext4_split_extent_at+0x6d/0x560

Call Trace:

<TASK>

ext4_split_extent.isra.0+0xcb/0x1b0

ext4_ext_convert_to_initialized+0x168/0x6c0

ext4_ext_handle_unwritten_extents+0x325/0x4d0

ext4_ext_map_blocks+0x520/0xdb0

ext4_map_blocks+0x2b0/0x690

ext4_iomap_begin+0x20e/0x2c0

[...]

==================================================================

Therefore, *orig_path is updated when the extent lookup succeeds, so that

the caller can safely use path or *ppath.