CVE-2024-46687: Vulnerability in Linux Linux

Severity: highType: vulnerabilityCVE-2024-46687

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix a use-after-free when hitting errors inside btrfs_submit_chunk() [BUG] There is an internal report that KASAN is reporting use-after-free, with the following backtrace: BUG: KASAN: slab-use-after-free in btrfs_check_read_bio+0xa68/0xb70 [btrfs] Read of size 4 at addr ffff8881117cec28 by task kworker/u16:2/45 CPU: 1 UID: 0 PID: 45 Comm: kworker/u16:2 Not tainted 6.11.0-rc2-next-20240805-default+ #76 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-3-gd478f380-rebuilt.opensuse.org 04/01/2014 Workqueue: btrfs-endio btrfs_end_bio_work [btrfs] Call Trace: dump_stack_lvl+0x61/0x80 print_address_description.constprop.0+0x5e/0x2f0 print_report+0x118/0x216 kasan_report+0x11d/0x1f0 btrfs_check_read_bio+0xa68/0xb70 [btrfs] process_one_work+0xce0/0x12a0 worker_thread+0x717/0x1250 kthread+0x2e3/0x3c0 ret_from_fork+0x2d/0x70 ret_from_fork_asm+0x11/0x20 Allocated by task 20917: kasan_save_stack+0x37/0x60 kasan_save_track+0x10/0x30 __kasan_slab_alloc+0x7d/0x80 kmem_cache_alloc_noprof+0x16e/0x3e0 mempool_alloc_noprof+0x12e/0x310 bio_alloc_bioset+0x3f0/0x7a0 btrfs_bio_alloc+0x2e/0x50 [btrfs] submit_extent_page+0x4d1/0xdb0 [btrfs] btrfs_do_readpage+0x8b4/0x12a0 [btrfs] btrfs_readahead+0x29a/0x430 [btrfs] read_pages+0x1a7/0xc60 page_cache_ra_unbounded+0x2ad/0x560 filemap_get_pages+0x629/0xa20 filemap_read+0x335/0xbf0 vfs_read+0x790/0xcb0 ksys_read+0xfd/0x1d0 do_syscall_64+0x6d/0x140 entry_SYSCALL_64_after_hwframe+0x4b/0x53 Freed by task 20917: kasan_save_stack+0x37/0x60 kasan_save_track+0x10/0x30 kasan_save_free_info+0x37/0x50 __kasan_slab_free+0x4b/0x60 kmem_cache_free+0x214/0x5d0 bio_free+0xed/0x180 end_bbio_data_read+0x1cc/0x580 [btrfs] btrfs_submit_chunk+0x98d/0x1880 [btrfs] btrfs_submit_bio+0x33/0x70 [btrfs] submit_one_bio+0xd4/0x130 [btrfs] submit_extent_page+0x3ea/0xdb0 [btrfs] btrfs_do_readpage+0x8b4/0x12a0 [btrfs] btrfs_readahead+0x29a/0x430 [btrfs] read_pages+0x1a7/0xc60 page_cache_ra_unbounded+0x2ad/0x560 filemap_get_pages+0x629/0xa20 filemap_read+0x335/0xbf0 vfs_read+0x790/0xcb0 ksys_read+0xfd/0x1d0 do_syscall_64+0x6d/0x140 entry_SYSCALL_64_after_hwframe+0x4b/0x53 [CAUSE] Although I cannot reproduce the error, the report itself is good enough to pin down the cause. The call trace is the regular endio workqueue context, but the free-by-task trace is showing that during btrfs_submit_chunk() we already hit a critical error, and is calling btrfs_bio_end_io() to error out. And the original endio function called bio_put() to free the whole bio. This means a double freeing thus causing use-after-free, e.g.: 1. Enter btrfs_submit_bio() with a read bio The read bio length is 128K, crossing two 64K stripes. 2. The first run of btrfs_submit_chunk() 2.1 Call btrfs_map_block(), which returns 64K 2.2 Call btrfs_split_bio() Now there are two bios, one referring to the first 64K, the other referring to the second 64K. 2.3 The first half is submitted. 3. The second run of btrfs_submit_chunk() 3.1 Call btrfs_map_block(), which by somehow failed Now we call btrfs_bio_end_io() to handle the error 3.2 btrfs_bio_end_io() calls the original endio function Which is end_bbio_data_read(), and it calls bio_put() for the original bio. Now the original bio is freed. 4. The submitted first 64K bio finished Now we call into btrfs_check_read_bio() and tries to advance the bio iter. But since the original bio (thus its iter) is already freed, we trigger the above use-after free. And even if the memory is not poisoned/corrupted, we will later call the original endio function, causing a double freeing. [FIX] Instead of calling btrfs_bio_end_io(), call btrfs_orig_bbio_end_io(), which has the extra check on split bios and do the pr ---truncated---

AI Analysis

Technical Summary

CVE-2024-46687 is a use-after-free vulnerability identified in the Btrfs (B-tree file system) implementation within the Linux kernel. The vulnerability arises in the function btrfs_submit_chunk(), which handles submission of bio (block I/O) requests for reading data. Specifically, when an error occurs during the processing of a bio that spans multiple stripes (e.g., a 128KB read crossing two 64KB stripes), the kernel incorrectly frees the original bio twice. The sequence involves splitting the bio into chunks, submitting the first chunk successfully, but encountering an error on the second chunk. In response to the error, the kernel calls btrfs_bio_end_io(), which frees the original bio. Later, when the first chunk completes, the kernel attempts to access the bio's iterator, which has already been freed, causing a use-after-free condition. This can lead to memory corruption, kernel crashes, or potentially arbitrary code execution within kernel context. The root cause is a double free of the bio structure due to improper error handling and cleanup logic. The fix involves replacing the call to btrfs_bio_end_io() with btrfs_orig_bbio_end_io(), which includes additional checks to prevent double freeing of split bios. This vulnerability was detected internally using Kernel Address Sanitizer (KASAN) and affects Linux kernel versions prior to the patch. No public exploits are currently known, but the flaw resides in a critical kernel subsystem responsible for file system integrity and I/O operations.

Potential Impact

For European organizations, the impact of CVE-2024-46687 can be significant, especially for those relying on Linux servers using the Btrfs file system for critical data storage and processing. Exploitation of this vulnerability could lead to kernel crashes (denial of service), data corruption, or privilege escalation if an attacker manages to execute arbitrary code in kernel space. This poses risks to data confidentiality, integrity, and availability. Organizations running cloud infrastructure, data centers, or embedded systems with vulnerable Linux kernels are at risk of operational disruption. Given the widespread use of Linux in European enterprises, government agencies, and critical infrastructure, exploitation could affect service continuity and data security. Although no active exploits are reported, the vulnerability's nature in kernel memory management makes it a high-value target for attackers seeking to compromise systems at a low level. Additionally, the complexity of the bug means that accidental triggering through malformed or corrupted I/O requests could cause system instability even without malicious intent.

Mitigation Recommendations

1. Immediate application of the official Linux kernel patch that replaces btrfs_bio_end_io() with btrfs_orig_bbio_end_io() in the btrfs_submit_chunk() function is critical. Monitor Linux kernel mailing lists and distributions for updated kernel packages addressing CVE-2024-46687. 2. For organizations unable to patch immediately, consider disabling or avoiding the use of Btrfs on critical systems until a patch is applied. 3. Implement strict input validation and monitoring on systems that accept untrusted I/O requests or run workloads that could trigger malformed bio submissions. 4. Employ kernel hardening techniques such as Kernel Address Sanitizer (KASAN) in testing environments to detect similar memory corruption issues proactively. 5. Maintain robust backup and recovery procedures to mitigate potential data loss from system crashes or corruption caused by exploitation attempts. 6. Monitor system logs and kernel crash reports for anomalies related to btrfs operations, which could indicate attempted exploitation or triggering of the vulnerability.