Executive Summary

This vulnerability exists in the Linux kernel's md/raid5 subsystem. It involves an issue with the handling of the llbitmap bit state during write operations on a degraded RAID 5 array. Specifically, when the llbitmap bit state is still unwritten, new writes should force a read-modify-write cycle (rcw) because the system checks if blocks are synced in handle_stripe_dirtying(). However, a similar check is missing later in the need_this_block() function. This causes the stripe handling process to enter a deadloop, as handle_stripe() attempts to proceed to handle_stripe_fill(), but need_this_block() always returns 0, resulting in no progress.

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Impact Analysis

This vulnerability can cause an IO hang in systems using degraded RAID 5 arrays in the Linux kernel. The deadloop in stripe handling means that write operations may stall indefinitely, potentially leading to system performance degradation, data unavailability, or system instability during RAID 5 degraded mode operations.

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