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 dont 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: 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.

Weakness

A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/11b230100d6801c014fab2afabc8bdea304c1b96
• https://git.kernel.org/stable/c/5b4b2dcace35f618fe361a87bae6f0d13af31bc1
• https://git.kernel.org/stable/c/6766937d0327000ac1b87c97bbecdd28b0dd6599
• https://git.kernel.org/stable/c/6801ed1298204d16a38571091e31178bfdc3c679
• https://git.kernel.org/stable/c/a9fcb1717d75061d3653ed69365c8d45331815cd
• https://git.kernel.org/stable/c/b63481b3a388ee2df9e295f97273226140422a42
• https://git.kernel.org/stable/c/ec0c0beb9b777cdd1edd7df9b36e0f3e67e2bdff
• https://git.kernel.org/stable/c/f55ecc58d07a6c1f6d6d5b5af125c25f8da0bda2