# CVE-2024-50254: linux: In the Linux kernel, the following vulnerability has been resolved:  bpf: Free dynamically allocated bits in bpf_iter...

CVE-2024-50254 is fixed in linux on 1 platform, first by DEBIAN-CVE-2024-50254, released November 9, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2024-50254
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0018
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Nov 9, 2024

## 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 "nr_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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.11.7-1 | [DEBIAN-CVE-2024-50254](https://patchblox.com/security/data/fix/linux/debian-cve-2024-50254.md) | Nov 9, 2024 |
| Linux | linux Debian 14 | 6.11.7-1 | [DEBIAN-CVE-2024-50254](https://patchblox.com/security/data/fix/linux/debian-cve-2024-50254.md) | Nov 9, 2024 |

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