CVE-2024-50254 Information

Description

In the Linux kernel the following vulnerability has been resolved:

bpf: Free dynamically allocated bits in bpf_iter_bits_destroy()

bpf_iter_bits_destroy() uses \kit->nr_bits <= 64\ to check whether the bits are dynamically allocated. However the check is incorrect and may cause a kmemleak as shown below:

unreferenced object 0xffff88812628c8c0 (size 32): comm \swapper/0\ pid 1 jiffies 4294727320 hex dump (first 32 bytes): b0 c1 55 f5 81 88 ff ff f0 f0 f0 f0 f0 f0 f0 f0 ..U……….. f0 f0 f0 f0 f0 f0 f0 f0 00 00 00 00 00 00 00 00 ………….. backtrace (crc 781e32cc): [<00000000c452b4ab>] kmemleak_alloc+0x4b/0x80 [<0000000004e09f80>] __kmalloc_node_noprof+0x480/0x5c0 [<00000000597124d6>] __alloc.isra.0+0x89/0xb0 [<000000004ebfffcd>] alloc_bulk+0x2af/0x720 [<00000000d9c10145>] prefill_mem_cache+0x7f/0xb0 [<00000000ff9738ff>] bpf_mem_alloc_init+0x3e2/0x610 [<000000008b616eac>] bpf_global_ma_init+0x19/0x30 [<00000000fc473efc>] do_one_initcall+0xd3/0x3c0 [<00000000ec81498c>] kernel_init_freeable+0x66a/0x940 [<00000000b119f72f>] kernel_init+0x20/0x160 [<00000000f11ac9a7>] ret_from_fork+0x3c/0x70 [<0000000004671da4>] ret_from_fork_asm+0x1a/0x30

That is because nr_bits will be set as zero in bpf_iter_bits_next() after all bits have been iterated.

Fix the issue by setting kit->bit to kit->nr_bits instead of setting kit->nr_bits to zero when the iteration completes in bpf_iter_bits_next(). In addition use !nr_bits || bits >= nr_bits\ to check whether the iteration is complete and still use r_bits > 64\ to indicate whether bits are dynamically allocated. The !nr_bits\ check is necessary because bpf_iter_bits_new() may fail before setting kit->nr_bits and this condition will stop the iteration early instead of accessing the zeroed or freed kit->bits.

Considering the initial value of kit->bits is -1 and the type of kit->nr_bits is unsigned int change the type of kit->nr_bits to int. The potential overflow problem will be handled in the following patch.

Reference

https://git.kernel.org/stable/c/9cee266fafaf79fd465314546f637f9a3c215830 https://git.kernel.org/stable/c/101ccfbabf4738041273ce64e2b116cf440dea13