bpf, verifier: Fix memory leak in array reallocation for stack state

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

bpf, verifier: Fix memory leak in array reallocation for stack state

If an error (NULL) is returned by krealloc(), callers of realloc_array()

were setting their allocation pointers to NULL, but on error krealloc()

does not touch the original allocation. This would result in a memory

resource leak. Instead, free the old allocation on the error handling

path.

The memory leak information is as follows as also reported by Zhengchao:

unreferenced object 0xffff888019801800 (size 256):

comm "bpf_repo", pid 6490, jiffies 4294959200 (age 17.170s)

hex dump (first 32 bytes):

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................

backtrace:

[<00000000b211474b>] __kmalloc_node_track_caller+0x45/0xc0

[<0000000086712a0b>] krealloc+0x83/0xd0

[<00000000139aab02>] realloc_array+0x82/0xe2

[<00000000b1ca41d1>] grow_stack_state+0xfb/0x186

[<00000000cd6f36d2>] check_mem_access.cold+0x141/0x1341

[<0000000081780455>] do_check_common+0x5358/0xb350

[<0000000015f6b091>] bpf_check.cold+0xc3/0x29d

[<000000002973c690>] bpf_prog_load+0x13db/0x2240

[<00000000028d1644>] __sys_bpf+0x1605/0x4ce0

[<00000000053f29bd>] __x64_sys_bpf+0x75/0xb0

[<0000000056fedaf5>] do_syscall_64+0x35/0x80

[<000000002bd58261>] entry_SYSCALL_64_after_hwframe+0x63/0xcd