badblocks: fix infinite loop due to incorrect rounding and overflow#774
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The roundup() and rounddown() macros return the rounded value but do not modify the input in place. In _badblocks_set(), _badblocks_clear(), and badblocks_check(), the return values were being discarded, causing s and target/next to remain unrounded. This resulted in sectors being calculated from unrounded values, which could lead to sectors being way too large (or zero), causing infinite loops in the re_insert/re_clear/re_check loops. Additionally, add integer overflow checks (s > ULLONG_MAX - sectors) before the s + sectors calculation in all three functions to prevent overflow-related issues. Also add early return when sectors becomes zero after rounding in badblocks_check(). Root cause: When s and sectors have specific values (e.g., from syzkaller fuzzing via nvdimm ioctl), the unrounded values cause sectors to be incorrectly calculated. In _badblocks_clear(), this could result in needing 2^46 iterations to process 2^55 sectors, triggering RCU stall warnings and effectively hanging the kernel. Fix by properly capturing the return values from roundup() and rounddown(), adding overflow checks before sector arithmetic, and handling the zero-sectors case in badblocks_check(). Signed-off-by: Ramesh Adhikari <adhikari.resume@gmail.com>
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Pull request for series with
subject: badblocks: fix infinite loop due to incorrect rounding and overflow
version: 1
url: https://patchwork.kernel.org/project/linux-block/list/?series=1086213