net: ethernet: ti: netcp: Standardize knav_dma_open_channel to return NULL on error

Summary

In the Linux kernel, the following vulnerability has been resolved: net: ethernet: ti: netcp: Standardize knav_dma_open_channel to return NULL on error Make knav_dma_open_channel consistently return NULL on error instead of ERR_PTR. Currently the header include/linux/soc/ti/knav_dma.h returns NULL when the driver is disabled, but the driver implementation does not even return NULL or ERR_PTR on failure, causing inconsistency in the users. This results in a crash in netcp_free_navigator_resources as followed (trimmed): Unhandled fault: alignment exception (0x221) at 0xfffffff2 [fffffff2] *pgd=80000800207003, *pmd=82ffda003, *pte=00000000 Internal error: : 221 [#1] SMP ARM Modules linked in: CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.17.0-rc7 #1 NONE Hardware name: Keystone PC is at knav_dma_close_channel+0x30/0x19c LR is at netcp_free_navigator_resources+0x2c/0x28c [... TRIM...] Call trace: knav_dma_close_channel from netcp_free_navigator_resources+0x2c/0x28c netcp_free_navigator_resources from netcp_ndo_open+0x430/0x46c netcp_ndo_open from __dev_open+0x114/0x29c __dev_open from __dev_change_flags+0x190/0x208 __dev_change_flags from netif_change_flags+0x1c/0x58 netif_change_flags from dev_change_flags+0x38/0xa0 dev_change_flags from ip_auto_config+0x2c4/0x11f0 ip_auto_config from do_one_initcall+0x58/0x200 do_one_initcall from kernel_init_freeable+0x1cc/0x238 kernel_init_freeable from kernel_init+0x1c/0x12c kernel_init from ret_from_fork+0x14/0x38 [... TRIM...] Standardize the error handling by making the function return NULL on all error conditions. The API is used in just the netcp_core.c so the impact is limited. Note, this change, in effect reverts commit 5b6cb43b4d62 ("net: ethernet: ti: netcp_core: return error while dma channel open issue"), but provides a less error prone implementation.