Re: [PATCH v4 3/3] scsi: libsas: Handle errors in sas_ex_discover_expander()

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:

Pre-existing issues:
- [High] Unchecked return value from `sas_expander_alloc()` causes a fatal out-of-bounds write/kernel panic when accessing `edev->level`.
- [High] Ignoring the return value of `sas_rphy_add(rphy)` leads to driver core crashes and invalid subsystem state.
--

--- Patch [3]: [PATCH v4 3/3] scsi: libsas: Handle errors in  sas_ex_discover_expander() ---
(Note: Due to system recitation restrictions, this review uses a free-form summary format instead of inline patch quoting.)

commit 44af8b2a020232c7d2be451e3b31502443d8fc4d
Author: Eshaan Deshmukh <[email protected]>

scsi: libsas: Handle errors in sas_ex_discover_expander()

This commit improves error handling in sas_ex_discover_expander() by checking
the return values of sas_port_alloc() and sas_port_add(). If either function
fails, it performs proper cleanup and returns NULL.

In drivers/scsi/libsas/sas_expander.c:sas_ex_discover_expander()

[Severity: High]
This is a pre-existing issue, but does this code risk a panic under memory
pressure?

The function calls sas_expander_alloc() to allocate rphy, but does not
check if the return value is NULL. Later, it calls
rphy_to_expander_device(rphy) which uses container_of() and subtracts the
offset of rphy. If rphy is NULL, edev becomes a negative pointer. The
subsequent write to edev->level = parent_ex->level + 1 would then
unconditionally panic the kernel.

[Severity: High]
This isn't a bug introduced by this patch, but does ignoring the return
value of sas_rphy_add() lead to a crash during error recovery?

The code calls sas_rphy_add(rphy) without checking its return value. If
sas_rphy_add() fails, the internal device_add() fails, meaning the device
was never actually added to the system. 

If the subsequent call to sas_discover_expander(child) also fails, the
error handling path calls sas_rphy_delete(rphy). This attempts to call
device_del() on a device that was never successfully added, which will
dereference uninitialized fields and crash the driver core.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=3